Lightweight Certificate Management Protocol (CMP) Profile
draft-ietf-lamps-lightweight-cmp-profile-05

Document Type Active Internet-Draft (lamps WG)
Authors Hendrik Brockhaus  , Steffen Fries  , David von Oheimb 
Last updated 2021-02-22
Replaces draft-brockhaus-lamps-lightweight-cmp-profile
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LAMPS Working Group                                    H. Brockhaus, Ed.
Internet-Draft                                                  S. Fries
Intended status: Standards Track                           D. von Oheimb
Expires: 26 August 2021                                          Siemens
                                                        22 February 2021

       Lightweight Certificate Management Protocol (CMP) Profile
              draft-ietf-lamps-lightweight-cmp-profile-05

Abstract

   The goal of this document is to facilitate interoperability and
   automation by profiling the Certificate Management Protocol (CMP)
   version 2, the related Certificate Request Message Format (CRMF)
   version 2, and the HTTP Transfer for the Certificate Management
   Protocol.  It specifies a subset of CMP and CRMF focusing on typical
   use cases relevant for managing certificates of devices in many
   industrial and IoT scenarios.  To limit the overhead of certificate
   management for more constrained devices only the most crucial types
   of operations are specified as mandatory.  To foster interoperability
   in more complex scenarios, other types of operations are specified as
   recommended or optional.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 26 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation for profiling CMP  . . . . . . . . . . . . . .   4
     1.2.  Motivation for a lightweight profile for CMP  . . . . . .   5
     1.3.  Existing CMP profiles . . . . . . . . . . . . . . . . . .   6
     1.4.  Compatibility with existing CMP profiles  . . . . . . . .   8
     1.5.  Scope of this document  . . . . . . . . . . . . . . . . .   9
     1.6.  Structure of this document  . . . . . . . . . . . . . . .  10
     1.7.  Convention and Terminology  . . . . . . . . . . . . . . .  11
   2.  Architecture and use cases  . . . . . . . . . . . . . . . . .  11
     2.1.  Solution architecture . . . . . . . . . . . . . . . . . .  12
     2.2.  Basic generic CMP message content . . . . . . . . . . . .  13
     2.3.  Supported PKI management operations . . . . . . . . . . .  13
       2.3.1.  Mandatory PKI management operations . . . . . . . . .  14
       2.3.2.  Recommended PKI management operations . . . . . . . .  14
       2.3.3.  Optional PKI management operations  . . . . . . . . .  15
     2.4.  CMP message transport . . . . . . . . . . . . . . . . . .  16
   3.  Generic parts of the PKI message  . . . . . . . . . . . . . .  17
     3.1.  General description of the CMP message header . . . . . .  18
     3.2.  General description of the CMP message protection . . . .  20
     3.3.  General description of CMP message extraCerts . . . . . .  21
   4.  End Entity PKI management operations  . . . . . . . . . . . .  21
     4.1.  Requesting a new certificate from a PKI . . . . . . . . .  22
       4.1.1.  Requesting a certificate from a new PKI with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  24
       4.1.2.  Requesting a certificate from a trusted PKI with
               signature protection  . . . . . . . . . . . . . . . .  30
       4.1.3.  Updating an existing certificate with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  31
       4.1.4.  Requesting a certificate from a PKI with MAC
               protection  . . . . . . . . . . . . . . . . . . . . .  32
       4.1.5.  Requesting a certificate from a legacy PKI using
               PKCS#10 request . . . . . . . . . . . . . . . . . . .  33
       4.1.6.  Generateing the key pair centrally at the PKI
               management entity . . . . . . . . . . . . . . . . . .  36
         4.1.6.1.  Using key agreement key management technique  . .  41
         4.1.6.2.  Using key transport key management technique  . .  43
         4.1.6.3.  Using password-based key management technique . .  43

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       4.1.7.  Delayed enrollment  . . . . . . . . . . . . . . . . .  44
     4.2.  Revoking a certificate  . . . . . . . . . . . . . . . . .  48
     4.3.  Error reporting . . . . . . . . . . . . . . . . . . . . .  50
     4.4.  Support messages  . . . . . . . . . . . . . . . . . . . .  52
       4.4.1.  Get CA certificates . . . . . . . . . . . . . . . . .  54
       4.4.2.  Get root CA certificate update  . . . . . . . . . . .  55
       4.4.3.  Get certificate request template  . . . . . . . . . .  56
   5.  LRA and RA PKI management operations  . . . . . . . . . . . .  59
     5.1.  Forwarding messages . . . . . . . . . . . . . . . . . . .  59
       5.1.1.  Not changing protection . . . . . . . . . . . . . . .  61
       5.1.2.  Replacing protection  . . . . . . . . . . . . . . . .  61
         5.1.2.1.  Keeping proof-of-possession . . . . . . . . . . .  62
         5.1.2.2.  Breaking proof-of-possession  . . . . . . . . . .  63
       5.1.3.  Adding Protection . . . . . . . . . . . . . . . . . .  63
         5.1.3.1.  Handling a single PKI management message  . . . .  64
         5.1.3.2.  Handling a batch of PKI management messages . . .  65
       5.1.4.  Initiating delayed enrollment . . . . . . . . . . . .  66
     5.2.  Revoking certificates on behalf of another's PKI
           entities  . . . . . . . . . . . . . . . . . . . . . . . .  66
     5.3.  Error reporting . . . . . . . . . . . . . . . . . . . . .  67
   6.  CMP message transport mechanisms  . . . . . . . . . . . . . .  67
     6.1.  HTTP transport  . . . . . . . . . . . . . . . . . . . . .  68
     6.2.  HTTPS transport using certificates  . . . . . . . . . . .  69
     6.3.  HTTPS transport using shared secrets  . . . . . . . . . .  70
     6.4.  Offline transport . . . . . . . . . . . . . . . . . . . .  70
       6.4.1.  File-based transport  . . . . . . . . . . . . . . . .  71
       6.4.2.  Other asynchronous transport protocols  . . . . . . .  71
     6.5.  CoAP transport  . . . . . . . . . . . . . . . . . . . . .  71
     6.6.  Piggybacking on other reliable transport  . . . . . . . .  71
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  71
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  71
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  72
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  72
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  72
     10.2.  Informative References . . . . . . . . . . . . . . . . .  73
   Appendix A.  Example CertReqTemplate  . . . . . . . . . . . . . .  75
   Appendix B.  History of changes . . . . . . . . . . . . . . . . .  77
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  81

1.  Introduction

   [RFC Editor: please delete]:!!! The change history was moved to
   Appendix B !!!

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   [RFC Editor: please delete]: The labels 'RFC-CMP-Updates', 'RFC-CMP-
   Alg', and 'RFC-CRMF-Alg' in ASN.1 Syntax needs to be replaced with
   the RFC numbers of CMP Updates [I-D.ietf-lamps-cmp-updates], CMP
   Algorithms [I-D.ietf-lamps-cmp-algorithms] and CRMF Algorithm
   Requirements Update [I-D.ietf-lamps-crmf-update-algs], when
   available.

   This document specifies PKI management operations supporting machine-
   to-machine and IoT use cases.  The focus lies on maximum automation
   and interoperable implementation of all involved PKI entities from
   end entities (EE) through an optional Local Registration Authority
   (LRA) and the RA up to the CA.  The profile makes use of the concepts
   and syntax specified in CMP [RFC4210], CRMF [RFC4211], HTTP transfer
   for CMP [RFC6712], and CMP Updates [I-D.ietf-lamps-cmp-updates].
   Especially CMP and CRMF are very feature-rich standards, while in
   most environments only a limited subset of the specified
   functionality is needed.  Additionally, the standards are not always
   precise enough on how to interpret and implement the described
   concepts.  Therefore, this document aims at tailoring and specifying
   in more detail how to use these concepts to implement lightweight
   automated certificate management.

1.1.  Motivation for profiling CMP

   CMP was standardized in 1999 and is implemented in several PKI
   products.  In 2005 a completely reworked and enhanced version 2 of
   CMP [RFC4210] and CRMF [RFC4211] has been published followed by a
   document specifying a transfer mechanism for CMP messages using HTTP
   [RFC6712] in 2012.

   Though CMP is a very solid and capable protocol it is so far not used
   very widely.  The most important reason appears to be that the
   protocol offers a too large set of features and options.  On the one
   hand, this makes CMP applicable to a very wide range of scenarios,
   but on the other hand a full implementation of all options is not
   realistic because this would take undue effort.

   Moreover, many details of the CMP protocol have been left open or
   have not been specified in full preciseness.  The profiles specified
   in Appendix D and E of [RFC4210] define some more detailed PKI
   management operations.  Yet the specific needs of highly automated
   scenarios for a machine-to-machine communication are not covered
   sufficiently.

   As also 3GPP and UNISIG already put across, profiling is a way of
   coping with the challenges mentioned above.  To profile means to take
   advantage of the strengths of the given protocol, while explicitly
   narrowing down the options it provides to those needed for the

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   purpose(s) at hand and eliminating all identified ambiguities.  In
   this way all the general and applicable aspects of the general
   protocol are taken over and only the peculiarities of the target
   scenario need to be dealt with specifically.

   Defining such a profile for a new target environment take a high
   effort because the range of available options needs to be well
   understood and the selected options need to be consistent with each
   other and with the intended usage scenario.  Since most industrial
   PKI management use cases typically have much in common it is worth
   sharing this effort, which is the aim of this document.  Other
   standardization bodies can reference this document and do not need to
   come up with individual profiles.

1.2.  Motivation for a lightweight profile for CMP

   The profiles specified in Appendix D and E of RFC 4210 [RFC4210] have
   been developed particularly for managing certificates of human end
   entities.  With the evolution of distributed systems and client-
   server architectures, certificates for machines and applications on
   them have become widely used.  This trend has strengthened even more
   in emerging industrial and IoT scenarios.  CMP is sufficiently
   flexible to support them well.

   Today's IT security architectures for industrial solutions typically
   use certificates for endpoint authentication within protocols like
   IPSec, TLS, or SSH.  Therefore, the security of these architectures
   highly relies upon the security and availability of the implemented
   certificate management procedures.

   Due to increasing security needs in operational networks as well as
   availability requirements, especially on critical infrastructures and
   systems with a high volume of certificates, a state-of-the-art
   certificate management must be constantly available and cost-
   efficient, which calls for high automation and reliability.  The NIST
   Framework for Improving Critical Infrastructure Cybersecurity
   [NIST.CSWP.04162018] also refers to proper processes for issuance,
   management, verification, revocation, and audit for authorized
   devices, users and processes involving identity and credential
   management.  Such PKI operation according to commonly accepted best
   practices is also required in IEC 62443-3-3 [IEC.62443-3-3] for
   security level 2 and higher.

   Further challenges in many industrial systems are network
   segmentation and asynchronous communication, while PKI operation
   typically is not deployed on-site but in a more protected environment
   of a data center or trust center.  Certificate management must be
   able to cope with such network architectures.  CMP offers the

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   required flexibility and functionality, namely self-contained
   messages, efficient polling, and support for asynchronous message
   transfer while retaining end-to-end security.

1.3.  Existing CMP profiles

   As already stated, RFC 4210 [RFC4210] contains profiles with
   mandatory and optional PKI management operations in Appendix D and E.
   Those profiles focus on management of human user certificates and do
   only partly address the specific needs for certificate management
   automation for unattended machines or application-oriented end
   entities.

   RFC 4210 [RFC4210] specifies in Appendix D the following mandatory
   PKI management operations.  All requirements regarding algorithm
   support have been updated by CMP Algorithms Section 7.2
   [I-D.ietf-lamps-cmp-algorithms], all operations may enroll up to two
   certificates, one for a locally generated and optionally another one
   for a centrally generated key pair, and all require use of certConf/
   pkiConf messages for confirmation.

   *  Initial registration/certification; an (uninitialized) end entity
      requests a (first) certificate from a CA using shared secret based
      message authentication.  The content is similar to the PKI
      management operation specified in Section 4.1.4 of this document.

   *  Certificate request; an (initialized) end entity requests another
      certificate from a CA using signature-based or shared secret-based
      message authentication.  The content is similar to the PKI
      management operation specified in Section 4.1.2 of this document.

   *  Key update; an (initialized) end entity requests a certificate
      from a CA (to update the key pair and/or corresponding certificate
      that it already possesses) using signature-based or shared secret-
      based message authentication.  The content is similar to the PKI
      management operation specified in Section 4.1.3 of this document.

   Two certificates may be enrolled and authentication is based on
   shared secrets because these PKI management operations focus on the
   enrollment of certificates of humans.

   RFC 4210 [RFC4210] specifies in Appendix E the following optional PKI
   management operations.  All requirements regarding algorithm support
   have been updated by CMP Algorithms Section 7.2
   [I-D.ietf-lamps-cmp-algorithms].

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   *  Root CA key update; a root CA updates its key pair and produces a
      CA key update announcement message, which can be made available
      (via some transport mechanism) to the relevant end entities.  This
      operation only supports a push model.  The content is similar to
      the PKI management operation supporting the pull model specified
      in Section 4.4.2 of this document.

   *  Information request/response; an end entity sends a general
      message to the PKI requesting details that will be required for
      later PKI management operations.  The content is similar to the
      PKI management operation specified in Section 4.4.3 of this
      document.

   *  Cross-certification request/response (1-way); creation of a single
      cross-certificate (i.e., not two at once).  The requesting CA MAY
      choose who is responsible for publication of the cross-certificate
      created by the responding CA through use of the PKIPublicationInfo
      control.

   *  In-band initialization using an external identity certificate
      (this PKI management operation may also enroll up to two
      certificates and requires use of certConf/pkiConf messages for
      confirmation as specified in Appendix D of RFC 4210 [RFC4210]).
      An (uninitialized) end entity wishes to initialize into the PKI
      with a CA, CA-1.  It uses, for authentication purposes, a pre-
      existing identity certificate issued by another (external) CA, CA-
      X.  A trust relationship must already have been established
      already between CA-1 and CA-X so that CA-1 can validate the EE's
      identity certificate signed by CA-X.  Furthermore, some mechanism
      must already have been established within the Personal Security
      Environment (PSE) of the EE enabling it to authenticate and verify
      PKIMessages signed by CA-1.  The content is similar to the PKI
      management operation specified in Section 4.1.1 of this document.

   Both these Appendixes D and E focus on EE-to-CA/RA PKI management
   operations and do not address further profiling of RA to CA
   communication as typically needed for full backend automation.

   3GPP makes use of CMP [RFC4210] in its Technical Specification 33.310
   [ETSI-3GPP.33.310] for automatic management of IPSec certificates in
   3G, LTE, and 5G backbone networks.  Since 2010 a dedicated CMP
   profile for initial certificate enrollment and certificate update
   operations between EE and RA/CA is specified in that document.

   UNISIG has included a CMP profile for certificate enrollment in the
   subset 137 specifying the ETRAM/ECTS on-line key management for train
   control systems [UNISIG.Subset-137] in 2015.

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   Both standardization bodies use CMP [RFC4210], CRMF [RFC4211], and
   HTTP transfer for CMP [RFC6712] to add tailored means for automated
   PKI management operations for unattended devices and services.

1.4.  Compatibility with existing CMP profiles

   The profile specified in this document is compatible with RFC 4210
   Appendixes D and E (PKI Management Message Profiles) [RFC4210], with
   the following exceptions:

   *  signature-based protection is the default protection; an initial
      PKI management operation may also use MAC-based protection,

   *  certification of a second key pair within the same PKI management
      operation is not supported,

   *  proof-of-possession (POPO) with self-signature of the certTemplate
      according to RFC 4210 Section 4.1 [RFC4210] clause 3 is the
      recommended default POPO method (deviations are possible for EEs
      when requesting central key generation, for (L)RAs when using
      raVerified, and if the newly generated keypair is technically not
      capable to generate digital signatures),

   *  confirmation of newly enrolled certificates may be omitted, and

   *  all PKI management operations consist of request-response message
      pairs originating at the EE, i.e., announcement messages
      (requiring the push model) are omitted.

   The profile specified in this document is compatible with the CMP
   profile for 3G, LTE, and 5G network domain security and
   authentication framework [ETSI-3GPP.33.310], except that:

   *  protection of initial PKI management operations may be MAC-based,

   *  the subject field is mandatory in certificate templates, and

   *  confirmation of newly enrolled certificates may be omitted.

   The profile specified in this document is compatible with the CMP
   profile for on-line key management in rail networks as specified in
   UNISIG Subset-137 [UNISIG.Subset-137], except that:

   *  A certificate enrollment request message consists of only one
      certificate request (CertReqMsg).  As UNISIG Subset-137 Table 6
      [UNISIG.Subset-137] allows to transport more than one certificate
      request message, this conflicts with this document.

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   *  As of RFC 4210 [RFC4210] the messageTime is required to be
      Greenwich Mean Time coded as generalizedTime As UNISIG Subset-137
      Table 5 [UNISIG.Subset-137] explicitly states that the messageTime
      in required to be 'UTC time', it is not clear if this means a
      coding as UTCTime or generalizedTime and if other time zones than
      Greenwich Mean Time shall be allowed.  Therefore, UNISIG
      Subset-137 [UNISIG.Subset-137] may conflict with RFC 4210
      [RFC4210].  Both time formats are described in RFC 5280
      Section 4.1.2.5 [RFC5280].

   *  This profile requires usage of the same type of protection for all
      messages of one PKI management operation.  This means, in case the
      request message is MAC protected, also the response, certConf, and
      pkiConf messages have a MAC-based protection.  As UNISIG
      Subset-137 Table 5 [UNISIG.Subset-137] specifies for the first
      certificate request MAC protection for all messages send by the
      client and signature protection for all messages send by the
      server, this conflicts with this document.

   *  Use of caPubs is not required but typically allowed in combination
      with MAC-based protected PKI management operations.  On the other
      hand UNISIG Subset-137 Table 12 [UNISIG.Subset-137] requires using
      caPubs.  Note that in case the protection of the response is
      changed to signature-based protection using a certificate issued
      under the root CA that is to be transported in the caPubs field,
      this is not a secure delivery of the root CA certificate.

   *  This profile requires that the certConf message has one CertStatus
      element where the statusInfo field is recommended.  In contrast,
      UNISIG Subset-137 Table 18 [UNISIG.Subset-137] requires that the
      certConf message has one CertStatus element where the statusInfo
      field must be absent.  This precludes sending a negative certConf
      message in case the EE rejects the newly enrolled certificate.
      This results in violating the general rule that a certificate
      request transaction must include a certConf message (since
      moreover using implicitConfirm is not allowed there, neither).

1.5.  Scope of this document

   This document specifies requirements on generating PKI management
   messages on the sender side.  It does not specify strictness of
   verification on the receiving side and how in detail to handle error
   cases.

   Especially on the EE side this profile aims at a lightweight
   implementation.  This means that the number of PKI management
   operations that implementations must support are reduced to a
   reasonable minimum to support most typical certificate management use

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   cases in industrial machine-to-machine environments.  On the EE side
   only limited resources are expected, while on the side of the PKI
   management entities the profile accepts higher resources needed.

   For the sake of robustness and preservation of security properties
   implementations should, as far as security is not affected, adhere to
   Postel's law: "Be conservative in what you do, be liberal in what you
   accept from others" (often reworded as: "Be conservative in what you
   send, be liberal in what you accept").

   When in Section 3, Section 4, and Section 5 a field of the ASN.1
   syntax as defined in RFC 4210 [RFC4210] and RFC 4211 [RFC4211] is not
   explicitly specified, it SHOULD not be used by the sending entity.
   The receiving entity MUST NOT require its absence and if present MUST
   gracefully handle its presence.

1.6.  Structure of this document

   Section 2 introduces the general PKI architecture and approach to
   certificate management using CMP that is assumed in this document.
   Then it enlists the PKI management operations specified in this
   document and describes them in general words.  The list of supported
   PKI management operations is divided into mandatory, recommended, and
   optional ones.

   Section 3 profiles the CMP message header, protection, and extraCerts
   fields as they are general elements of CMP messages.

   Section 4 profiles the exchange of CMP messages between an EE and the
   first PKI management entity.  There are various flavors of
   certificate enrollment requests, optionally with polling, revocation,
   error handling, and general support PKI management operations.

   Section 5 profiles the message exchange between PKI management
   entities.  In the first place this consists of forwarding messages
   coming from or going to an EE.  This may include delayed delivery of
   messages, which involves polling for certificate responses.
   Additionally, it specifies operations where a PKI management entity
   manages certificates on behalf of an EE or for itself.

   Section 6 outlines several mechanisms for CMP message transfer,
   namely HTTP-based transfer as already specified in RFC 6712
   [RFC6712], using an additional TLS layer, or offline file-based
   transport.  CoAP [RFC7252] and piggybacking CMP messages

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1.7.  Convention and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown
   here.

   Technical terminology is used in conformance with RFC 4210 [RFC4210],
   RFC 4211 [RFC4211], RFC 5280 [RFC5280], and IEEE 802.1AR
   [IEEE.802.1AR_2018].  The following key words are used:

   CA:   Certification authority, which issues certificates.

   RA:   Registration authority, an optional PKI component to which a CA
         delegates certificate management functions such as
         authorization checks.

   LRA:  Local registration authority, an optional RA system component
         with proximity to the end entities.

   KGA:  Key generation authority, an optional system component,
         typically co-located with an LRA, RA, or CA, that offers key
         generation services to end entities.

   EE:   End entity, a user, device, or service that holds public-
         private key pair for which it manages a public-key certificate.
         An identifier for the EE is given as the subject of its
         certificate.

   The following terminology is reused from RFC 4210 [RFC4210] and used
   as follows:

   PKI management operation:  All CMP messages belonging to one
                              transaction context.  The transaction is
                              identified in the transactionID field of
                              the message header.

   PKI management entity:     All non-EE PKI entities such as LRA, RA,
                              and CA.

   PKI entity:                EEs and PKI management entities

2.  Architecture and use cases

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2.1.  Solution architecture

   In order to facilitate secure automatic certificate enrollment if the
   device hosting an EE is equipped with a manufacturer issued
   certificate during production.  Such a manufacturer issued
   certificate is installed during production to identify the device
   throughout its lifetime.  This manufacturer certificate can be used
   to protect the initial enrollment of operational certificates after
   installation of the EE on site in its operational environment.  An
   operational certificate is issued by the owner or operator of the
   device to identify the device during operation for use, e.g., in a
   security protocol like IPSec, TLS, or SSH.  In IEEE 802.1AR
   [IEEE.802.1AR_2018] a manufacturer certificate is called IDevID
   certificate and an operational certificate is called LDevID
   certificate.

   Note: According to IEEE 802.1AR [IEEE.802.1AR_2018] a DevID comprises
   the triplet of the certificate and the corresponding private key as
   well as certificate chain up to the root certificate.

   All certificate management transactions specified in this document
   are initiated by the EE.  The EE creates a CMP request message,
   protects it using some asymmetric credential or shared secret
   information, as far as available, and sends it to its locally
   reachable PKI component.  This PKI component may be an LRA, RA, or
   the CA, which checks the request, responds to it itself, or forwards
   the request upstream to the next PKI component.  In case an (L)RA
   changes the CMP request message header or body or wants to prove a
   successful verification or authorization, it can apply a protection
   of its own.  Especially the communication between an LRA and RA can
   be performed synchronously or asynchronously.  Synchronous
   communication describes a timely uninterrupted communication between
   two communication partners, while asynchronous communication is not
   performed in a timely consistent manner, e.g., because of a delayed
   message delivery.

   +-----+            +-----+                +-----+            +-----+
   |     |            |     |                |     |            |     |
   | EE  |<---------->| LRA |<-------------->| RA  |<---------->| CA  |
   |     |            |     |                |     |            |     |
   +-----+            +-----+                +-----+            +-----+

           synchronous        (a)synchronous       (a)synchronous
      +----connection----+------connection------+----connection----+

           on site at                operators          service partner
   +----------plant---------+-----backend services-----+-trust center-+

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                  Figure 1: Certificate management on site

   In operation environments a layered LRA-RA-CA architecture can be
   deployed, e.g., with LRAs bundling requests from multiple EEs at
   dedicated locations and one (or more than one) central RA aggregating
   the requests from multiple LRAs.  Every (L)RA in this scenario
   typically has a shared secret information (one per EE) for password-
   based protection or a CMP protection key and certificate containing
   an extended key usage as specified in CMP Updates
   [I-D.ietf-lamps-cmp-updates] allowing it to protect CMP messages it
   processes.  The figure above shows an architecture using one LRA and
   one RA.  It is also possible to have only an RA or multiple LRAs and/
   or RAs.  Depending on the network infrastructure, the message
   transfer between PKI management entities may be based on synchronous
   online connections, delayed asynchronous connections, or even offline
   (e.g., file-based) transfer.

   This profile focusses on specifying the pull model, where the EE
   always requests a specific PKI management operation.

   Note: CMP response messages, especially in case of central key
   generation, as described in Section 4.1.6, could also be used
   proactively to implement the push model towards the EE.

   Third-party CAs typically implement other variants of CMP, different
   standardized protocols, or even proprietary interfaces for
   certificate management.  Therefore, the LRA or the RA may need to
   adapt the exchanged CMP messages to the flavor of certificate
   management interaction required by the CA.

2.2.  Basic generic CMP message content

   Section 3 specifies the generic parts of the CMP messages as used
   later in Section 4 and Section 5.

   *  Header of a CMP message; see Section 3.1.

   *  Protection of a CMP message; see Section 3.2.

   *  ExtraCerts field of a CMP message; see Section 3.3.

2.3.  Supported PKI management operations

   Following the scope outlined in Section 1.5, this section gives a
   brief overview of the PKI management operations specified in
   Section 4 and Section 5 and states whether implementation by
   compliant EE or PKI management entities is mandatory, recommended, or
   optional.

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2.3.1.  Mandatory PKI management operations

   The mandatory PKI management operations in this document limit the
   overhead of certificate management.  This minimal set of operations
   may be helpful for keeping development effort low and for use in
   memory-constrained devices.

   +=======================================+=========+
   | PKI management operations             | Section |
   +=======================================+=========+
   | Request a certificate from a new PKI  | Section |
   | with signature protection             | 4.1.1   |
   +---------------------------------------+---------+
   | Request to update an existing         | Section |
   | certificate with signature protection | 4.1.3   |
   +---------------------------------------+---------+
   | Error reporting                       | Section |
   |                                       | 4.3     |
   +---------------------------------------+---------+

       Table 1: Mandatory End Entity PKI management
                        operations

   +===============================================+===============+
   | PKI management operations                     | Section       |
   +===============================================+===============+
   | Forward messages without changes              | Section 5.1.1 |
   +-----------------------------------------------+---------------+
   | Forward messages with replaced protection and | Section       |
   | keeping the original proof-of-possession      | 5.1.2.1       |
   +-----------------------------------------------+---------------+
   | Forward messages with replaced protection and | Section       |
   | setting raVerified as proof-of-possession     | 5.1.2.2       |
   +-----------------------------------------------+---------------+
   | Error reporting                               | Section 5.3   |
   +-----------------------------------------------+---------------+

        Table 2: Mandatory LRA and RA PKI management operations

2.3.2.  Recommended PKI management operations

   Additional recommended PKI management operations shall support some
   more complex scenarios, that are considered beneficial for
   environments with more specific boundary conditions.

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   +======================================================+=========+
   | PKI management operations                            | Section |
   +======================================================+=========+
   | Request a certificate from a PKI with MAC protection | Section |
   |                                                      | 4.1.4   |
   +------------------------------------------------------+---------+
   | Revoke a certificate of its own                      | Section |
   |                                                      | 4.2     |
   +------------------------------------------------------+---------+

       Table 3: Recommended End Entity PKI management operations

   +========================================+=============+
   | PKI management operations              | Section     |
   +========================================+=============+
   | Revoke a certificate of another entity | Section 5.2 |
   +----------------------------------------+-------------+

        Table 4: Recommended LRA and RA PKI management
                          operations

2.3.3.  Optional PKI management operations

   The optional PKI management operations support specific requirements
   seen only in some environments with special requirements.

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   +========================================================+=========+
   | PKI management operations                              | Section |
   +========================================================+=========+
   | Request a certificate from a trusted PKI with          | Section |
   | signature protection                                   | 4.1.2   |
   +--------------------------------------------------------+---------+
   | Request a certificate from a legacy PKI using a        | Section |
   | PKCS#10 [RFC2986] request                              | 4.1.5   |
   +--------------------------------------------------------+---------+
   | Add central generation of a key pair to a certificate  | Section |
   | request.  (If central key generation is supported, the | 4.1.6   |
   | key agreement key management technique is REQUIRED to  |         |
   | be supported, and the key transport and password-based |         |
   | key management techniques are OPTIONAL.)               |         |
   +--------------------------------------------------------+---------+
   | Handle delayed enrollment due to asynchronous or       | Section |
   | offline message delivery                               | 4.1.7   |
   +--------------------------------------------------------+---------+
   | Additional support messages - distribution of CA       | Section |
   | certificates, update of a root CA certificate and      | 4.4     |
   | provisioning of certificate request template           |         |
   +--------------------------------------------------------+---------+

          Table 5: Optional End Entity PKI management operations

   +=============================================+===============+
   | PKI management operations                   | Section       |
   +=============================================+===============+
   | Forward messages with additional protection | Section 5.1.3 |
   +---------------------------------------------+---------------+
   | Initiate delayed enrollment due to          | Section 5.1.4 |
   | asynchronous or offline message delivery    |               |
   +---------------------------------------------+---------------+

        Table 6: Optional LRA and RA PKI management operations

2.4.  CMP message transport

   On different links between PKI entities, e.g., EE-RA and RA-CA,
   different transport MAY be used.  As CMP does not have specific needs
   regarding message transport, virtually any reliable transport
   mechanism may be used, e.g., HTTP, CoAP, and offline file-based
   transport.  Therefore, this document does not require any specific
   transport protocol to be supported by conforming implementations.

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   HTTP transfer is RECOMMENDED to use for all PKI entities, yet full
   flexibility is retained to choose whatever transport is suitable, for
   instance for devices with special constraints.

   +==================================+=============+
   | Transport                        | Section     |
   +==================================+=============+
   | Transfer CMP messages using HTTP | Section 6.1 |
   +----------------------------------+-------------+

       Table 7: Recommended transport mechanisms

   +========================================+=========+
   | Transport                              | Section |
   +========================================+=========+
   | Transfer CMP messages using HTTPS with | Section |
   | certificate-based authentication       | 6.2     |
   +----------------------------------------+---------+
   | Transfer CMP messages using HTTPS with | Section |
   | shared secret-based authentication     | 6.3     |
   +----------------------------------------+---------+
   | Offline CMP message transport          | Section |
   |                                        | 6.4     |
   +----------------------------------------+---------+
   | Transfer CMP messages using CoAP       | Section |
   |                                        | 6.5     |
   +----------------------------------------+---------+

          Table 8: Optional transport mechanisms

3.  Generic parts of the PKI message

   The generic parts of the CMP message profiles specified in Section 4
   and Section 5 are standardized to the maximum extent possible and are
   described centrally in this section to reduce redundancy in the
   description and to ease implementation.

   As described in section 5.1 of [RFC4210], all CMP messages have the
   following general structure:

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              +--------------------------------------------+
              | PKIMessage                                 |
              | +----------------------------------------+ |
              | | header                                 | |
              | +----------------------------------------+ |
              | +----------------------------------------+ |
              | | body                                   | |
              | +----------------------------------------+ |
              | +----------------------------------------+ |
              | | protection (OPTIONAL)                  | |
              | +----------------------------------------+ |
              | +----------------------------------------+ |
              | | extraCerts (OPTIONAL)                  | |
              | +----------------------------------------+ |
              +--------------------------------------------+

                      Figure 2: CMP message structure

   The general contents of the message header, protection, and
   extraCerts fields are specified in the following subsections.

   In case a specific CMP message profile needs different contents in
   the header, protection, or extraCerts fields, the differences are
   described in the respective message profile.

   The CMP message body contains the message-specific information.  It
   is described as part Section 4 and Section 5.

   The behavior in case an error occurs while handling the generic parts
   of a CMP message is described in Section 5.3.

3.1.  General description of the CMP message header

   This section describes the generic header field of all CMP messages
   with signature-based protection.  The only variations described here
   are in the recipient, transactionID, and recipNonce fileds of the
   first message of a PKI management operation.

   In case a message has MAC-based protection the changes are described
   in Section 4.1.4.  The variations will affect the fields sender,
   protectionAlg, and senderKID.

   For requirements regarding proper random number generation please
   refer to [RFC4086].  Any message-specific fields or variations are
   described in Section 4 and Section 5.

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   header
     pvno                        REQUIRED
       -- MUST be set to 3 to indicate CMP V3 in all cases where
       -- EnvelopedData is supported and expected to be used in this PKI
       -- management operation
       -- MUST be set to 2 to indicate CMP V2 in all other cases
       -- For details on version negotiation see RFC-CMP-Updates
     sender                      REQUIRED
       -- MUST contain a name representing the originator of the message
       -- SHOULD be the subject of the CMP protection certificate, i.e.,
       -- the certificate for the private key used to sign the message
     recipient                   REQUIRED
       -- SHOULD be the name of the intended recipient and
       -- MAY be a NULL-DN, i.e., a zero-length SEQUENCE OF
       -- RelativeDistinguishedNames, if the sender does not know the
       -- DN of the recipient
       -- If this is the first message of a transaction: SHOULD be the
       -- subject of the issuing CA certificate
       -- In all other messages: SHOULD be the same name as in the
       -- sender field of the previous message in the same transaction
     messageTime                 RECOMMENDED
       -- MUST be the time at which the message was produced, if
       -- present
     protectionAlg               REQUIRED
       -- MUST be the algorithm OID of the algorithm used for
       -- calculating the protection bits
       -- The signature algorithm MUST be a MSG_SIG_ALG as specified in
       -- RFC-CMP-Alg Section 3 and MUST be consistent with the
       -- subjectPublicKeyInfo field of the protection certificate
       -- The MAC algorithm MUST be a MSG_MAC_ALG as specified in
       -- RFC-CMP-Alg Section 6
       algorithm                 REQUIRED
       -- MUST be the OID of the signature or MAC algorithm
     senderKID                   RECOMMENDED
       -- MUST be the SubjectKeyIdentifier of the CMP protection
       -- certificate or a reference of the shared secret information
       -- used for the protection
     transactionID               REQUIRED
       -- If this is the first message of a transaction:
       -- MUST be 128 bits of random data for the start of a
       -- transaction, to minimize the probability of having the
       -- transactionID already in use at the server
       -- In all other messages:
       -- MUST be the value from the previous message in the same
       -- transaction
     senderNonce                 REQUIRED
       -- MUST be cryptographically secure and fresh 128 random bits
     recipNonce                  RECOMMENDED

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       -- If this is the first message of a transaction: SHOULD be
       -- absent
       -- In all other messages: MUST be present and contain the value
       -- of the senderNonce of the previous message in the same
       -- transaction
     generalInfo                 OPTIONAL
       implicitConfirm           OPTIONAL
       -- The field is optional in ir/cr/kur/p10cr requests and
       -- ip/cp/kup response messages and PROHIBTED in other types of
       -- messages
       -- Added to request messages to request omission of the certConf
       -- message
       -- See [RFC4210] Section 5.1.1.1.
       -- Added to response messages to grant omission of the certConf
       -- message
         ImplicitConfirmValue    REQUIRED
       -- ImplicitConfirmValue of the request message MUST be NULL if
       -- the EE wants to request not to send a confirmation message
       -- ImplicitConfirmValue MUST be NULL if the PKI management
       -- entity wants to grant not sending a confirmation message

3.2.  General description of the CMP message protection

   This section describes the generic protection field of all CMP
   messages with signature-based protection.  The certificate for the
   private key used to sign a CMP message is called 'protection
   certificate'.  Any included keyUsage extension SHOULD allow
   digitalSignature.

   protection                    RECOMMENDED
       -- MUST contain the signature calculated using the private key
       -- of the entity protecting the message. The signature
       -- algorithm used MUST be given in the protectionAlg field.

   Generally, CMP message protection is required for CMP messages, but
   there are cases where protection of error messages as specified in
   Section 4.3 and Section 5.3 is not possible and therefore MAY be
   omitted.

   For MAC-based protection as specified in Section 4.1.4 major
   differences apply as described in the respective section.

   The CMP message protection provides, if available, message origin
   authentication and integrity protection for the CMP message header
   and body.  The CMP message extraCerts field is not covered by this
   protection.

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   Note: The extended key usages specified in CMP Updates
   [I-D.ietf-lamps-cmp-updates] can be used for authorization of a
   sending PKI management entity.

   Note: The requirements for checking certificates given in [RFC5280]
   MUST be the followed for signature-based CMP message protection.  In
   case the CMP protection certificate is not the CA certificate that
   signed the newly issued certificate, certificate status checking
   SHOULD be used for the CMP protection certificates of communication
   partners.

3.3.  General description of CMP message extraCerts

   This section describes the generic extraCerts field of all CMP
   messages with signature-based protection.  If extraCerts are
   required, recommended, or optional is specified in the respective PKI
   management operation.

   extraCerts
       -- SHOULD contain the CMP protection certificate together with
       -- its chain, if needed and the self-signed root certificate
       -- SHOULD be omitted
       -- If present, the first certificate in this field MUST be
       -- the CMP protection certificate and each followed by its chain
       -- where each element SHOULD directly certify the one
       -- immediately preceding it.
       -- Self-signed certificates SHOULD be omitted from extraCerts,
       -- unless they are the same as the protection certificate and
       -- MUST NOT be trusted based on their inclusion in any case

   Note: For maximum compatibility, all implementations SHOULD be
   prepared to handle potentially additional certificates and arbitrary
   orderings of the certificates.

4.  End Entity PKI management operations

   This chapter focuses on the communication of the EE with the PKI
   management entity it immediately talks to.  Depending on the network
   and PKI solution, this can be an LRA, RA, or directly a CA.

   The PKI management operations specified in this section cover the
   following:

   *  Requesting a certificate from a PKI with variations like initial
      enrollment and updates, central key generation, and various
      protection mechanisms

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   *  Revocation of a certificate

   *  General messages for further support functions

   These operations mainly specify the message body of the CMP messages
   and utilize the specification of the message header, protection and
   extraCerts as specified in Section 4.

   The behavior in case an error occurs is described in Section 4.3.

   This section is aligned with RFC 4210 [RFC4210].  The general rules
   for interpretation stated in Appendix D.1 of RFC 4210 [RFC4210] shall
   be applied here, too.

   Guidelines as well as an algorithm use profile for this document are
   available in CMP Algorithms [draft-ietf-lamps-cmp-algorithms].

4.1.  Requesting a new certificate from a PKI

   There are various approaches for requesting a certificate from a PKI.

   These approaches differ in the way the EE authenticates itself to the
   PKI and in the way that the key pair to be certified is generated.
   The authentication mechanisms may be as follows:

   *  Using a certificate from a trusted PKI and the corresponding
      private key, e.g., a manufacturer issued certificate

   *  Using the certificate to be updated and the corresponding private
      key

   *  Using shared secret information known to the EE and the PKI

   An EE requests a certificate indirectly or directly from a CA.  When
   the PKI management entity responds with a message containing the
   requested certificate, the EE MUST reply with a confirmation message.
   The PKI management entity then MUST respond with a confirmation,
   closing the transaction.

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   The message sequences in this section allow the EE to request
   certification of a locally generated public-private key pair.  For
   requirements regarding proper random number and key generation please
   refer to [RFC4086].  The EE SHOULD provide a signature-based proof-
   of-possession of the private key associated with the public key
   contained in the certificate request as defined by RFC 4211
   Section 4.1 [RFC4211] case 3.  To this end it is assumed that the
   private key can technically be used for signing.  This is the case
   for the most commonly used algorithms RSA and ECDSA, regardless of
   potentially intended restrictions of the key usage.

   Note: In conformance with NIST SP 800-57 Part 1 Section 8.1.5.1.1.2
   [NIST.SP.800-57p1r5] the newly generated private key MAY be used for
   self-signature, if technically possible, even if the keyUsage
   extension requested in the certificate request prohibits generation
   of digital signatures.

   The requesting EE provides the binding of the proof-of-possession to
   its identity by signature-based or MAC-based protection of the CMP
   request message containing that POPO.  As will be detailed in
   Section 5.1.2, the targeted PKI management entity should verify
   whether this EE is authorized to obtain a certificate with the
   requested subject and other fields and extensions.  Especially when
   removing the protection provided by the EE and applying a new
   protection, the PKI management entity MUST verify in particular the
   included proof-of-possession self-signature of the certTemplate or
   the PKCS#10 certificationRequestInfo using the public key of the
   requested certificate and MUST check that the EE, as authenticated by
   the message protection, is authorized to request a certificate with
   the subject as specified in the certTemplate.

   When an EE verifies the protection of a response message with
   signature-based protection it needs a trust anchor to verify the
   protection certificate.  There are several ways to install the Root
   CA certificate of a new PKI on an EE.  The installation can be
   performed in an out-of-band manner, using general messages, a voucher
   [RFC8366], or other formats for enrollment, or in-band of CMP by the
   caPubs field in the certificate response message.  In case the
   installation of the new root CA certificate is performed using the
   caPubs field, the certificate response message MUST be properly
   authenticated, and the sender of this message MUST be authorized to
   install new root CA certificates on the EE.  This authorization is
   typically indicated by using shared secret information, but it can
   also be indicated by using a private key with a certificate issued by
   another PKI authorized for this purpose, for the CMP message
   protection.

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4.1.1.  Requesting a certificate from a new PKI with signature
        protection

   This PKI management operation should be used by an EE to request a
   certificate from a new PKI using an existing certificate from an
   external PKI, e.g., a manufacturer-issued IDevID certificate
   [IEEE.802.1AR_2018], to authenticate itself to the new PKI.  The EE
   already has established trust in this new PKI it is about to enroll
   to, e.g., by voucher exchange or configuration means.  The
   certificate request message is signature-protected using the existing
   certificate from the external PKI.

   Preconditions:

   1  The EE MUST have a certificate enrolled by an external PKI in
      advance to this PKI management operation to authenticate itself to
      the PKI management entity using signature-based protection, e.g.,
      using a manufacturer issued certificate.

   2  The EE SHOULD know the subject name of the new CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of
      the CA, the PKI management entity MUST know where to route these
      requests to.

   3  The EE MUST authenticate responses from the PKI management entity;
      trust MAY be established using an enrollment voucher or other
      configuration means.

   4  The PKI management entity MUST trust the external PKI the EE uses
      to authenticate itself; trust MAY be established using some
      configuration means.

   The general message flow for this PKI management operation is like
   that given in RFC 4210 Appendix E.7 [RFC4210].

   Message flow:

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   Step# EE                                  PKI management entity
     1   format ir
     2                      ->   ir      ->
     3                                        handle, re-protect or
                                                forward ir
     4                                        format or receive ip
     5                                        possibly grant implicit
                                                confirm
     6                      <-   ip      <-
     7   handle ip
     8                                        In case of status
                                                "rejection" in the
                                                ip message, no certConf
                                                and pkiConf are sent
     9   format certConf (optional)
    10                      ->   certConf ->
    11                                        handle, re-protect or
                                                forward certConf
    12                                        format or receive pkiConf
    13                      <-   pkiconf  <-
    14   handle pkiConf (optional)

   For this PKI management operation, the EE MUST include exactly one
   single CertReqMsg in the ir.  If more certificates are required,
   further requests MUST be sent using separate PKI management
   operation.  If the EE wants to omit sending a certificate
   confirmation message after receiving the ip, e.g., to reduce the
   number of protocol messages exchanged in this PKI management
   operation, it MUST request this by including the implicitConfirm
   extension in the header of the ir message, see Section 3.1.

   If the request was accepted and a new certificate was issued by the
   CA, the PKI management entity MUST return the new certificate in the
   certifiedKeyPair field of the ip message.  If the EE requested
   omission of the certConf message, the PKI management entity MAY grant
   this by including the implicitConfirm extension, else this is
   rejected by not including the implicitConfirm field in the ip
   message.

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   If the EE did not request implicit confirmation or the request was
   not granted by the PKI management entity, certificate confirmation
   MUST be performed as follows.  If the EE successfully received the
   certificate and accepts it, the EE MUST send a certConf message,
   which the PKI management entity must respond using a pkiConf message.
   If the PKI management entity does not receive the expected certConf
   message in time it MUST handle this like a rejection by the EE.  In
   this case the PKI management entity SHALL terminate the PKI
   management operation.  The PKI MAY revoke the newly issued
   certificates depending on the local policy.

   If the certificate request was rejected by the CA, the PKI management
   entity must return an ip message containing the status code
   "rejection" as described in Section 5.3 and no certifiedKeyPair
   field.  The EE MUST NOT react to such an ip message with a certConf
   message and the PKI management operation MUST be terminated.

   Detailed message description:

   Certification Request -- ir

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The request of the EE for a new certificate
     ir                          REQUIRED
       -- MUST be exactly one CertReqMsg
       -- If more certificates are required, further requests MUST be
       -- packaged in separate PKI Messages
       certReq                   REQUIRED
         certReqId               REQUIRED
       -- MUST be set to 0
         certTemplate            REQUIRED
           version               OPTIONAL
       -- MUST be 2 if supplied.
           subject               REQUIRED
       -- The EE subject name MUST be carried in the subject field
       -- and/or the subjectAltName extension.
       -- If subject name is present only in the subjectAltName
       -- extension, then the subject field MUST be a NULL-DN
           publicKey             REQUIRED
             algorithm           REQUIRED
       -- MUST include the subject public key algorithm OID and valueany
       -- parameters
       -- In case a central key generation is requested, this field

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       -- contains the algorithm and parameter preferences of the
       -- requesting entity regarding the to-be-generated key pair
             subjectPublicKey    REQUIRED
       -- MUST contain the public key to be certified in case of
       -- local key generation
       -- MUST contain a zero-length BIT STRING in case a central key
       -- generation is requested
           extensions            OPTIONAL
       -- MAY include end-entity-specific X.509 extensions of the
       -- requested certificate like subject alternative name,
       -- key usage, and extended key usage
       -- The subjectAltName extension MUST be present if the EE
       -- subject name includes a subject alternative name.
       Popo                      REQUIRED
         POPOSigningKey          OPTIONAL
       -- MUST be used in case subjectPublicKey contains a public key
       -- MUST be absent in case subjectPublicKey contains a
       -- zero-length BIT STRING
           poposkInput           PROHIBITED
       -- MUST NOT be used; it is not needed because subject and
       -- publicKey are both present in the certTemplate
           algorithmIdentifier   REQUIRED
       -- The signature algorithm MUST be consistent with the
       -- publicKey field of the certTemplate
           signature             REQUIRED
       -- MUST be the signature computed over the DER-encoded
       -- certTemplate

   protection                    REQUIRED
       -- As described in Section 3.2

   extraCerts                    REQUIRED
       -- As described in Section 3.3

   Certification Response -- ip

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The response of the CA to the request as appropriate
     ip                          REQUIRED
       caPubs                    OPTIONAL
       -- MAY be used
       -- If used it MUST contain only the root certificate of the

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       -- certificate contained in certOrEncCert
       response                  REQUIRED
       -- MUST be exactly one CertResponse
         certReqId               REQUIRED
       -- MUST be set to 0
         status                  REQUIRED
       -- PKIStatusInfo structure MUST be present
           status                REQUIRED
       -- positive values allowed: "accepted", "grantedWithMods"
       -- negative values allowed: "rejection"
           statusString          OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI
           failInfo              OPTIONAL
       -- MUST be present if status is "rejection"
       -- MUST be absent if the status is "accepted" or
       -- "grantedWithMods"
         certifiedKeyPair        OPTIONAL
       -- MUST be present if status is "accepted" or "grantedWithMods"
       -- MUST be absent if status is "rejection"
           certOrEncCert         REQUIRED
       -- MUST be present when certifiedKeyPair is present
             certificate         REQUIRED
       -- MUST be present when certifiedKeyPair is present
       -- MUST contain the newly enrolled X.509 certificate
           privateKey            OPTIONAL
       -- MUST be absent in case of local key-generation
       -- MUST contain the encrypted private key in an EnvelopedData
       -- structure as specified in section 5.1.5 in case the private
       -- key was generated centrally

   protection                    REQUIRED
       -- As described in Section 3.2

   extraCerts                    REQUIRED
       -- As described in Section 3.3
       -- MUST contain the chain of the certificate present in
       -- certOrEncCert
       -- Self-signed root certificate SHOULD be omitted
       -- Duplicate certificates MAY be omitted

   Certificate Confirmation -- certConf

   Field                         Value

   header
       -- As described in Section 3.1

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   body
       -- The message of the EE sends confirmation to the PKI
       -- management entity to accept or reject the issued certificates
     certConf                    REQUIRED
       -- MUST be exactly one CertStatus
       CertStatus                REQUIRED
         certHash                REQUIRED
       -- MUST be the hash of the certificate, using the same hash
       -- algorithm as used to create the certificate signature
         certReqId               REQUIRED
       -- MUST be set to 0
         statusInfo              RECOMMENDED
       -- PKIStatusInfo structure SHOULD be present
       -- Omission indicates acceptance of the indicated certificate
           status                REQUIRED
       -- positive values allowed: "accepted"
       -- negative values allowed: "rejection"
           statusString          OPTIONAL
       -- MAY be any human-readable text for debugging, logging, or to
       -- display in a GUI
           failInfo              OPTIONAL
       -- MUST be present if status is "rejection"
       -- MUST be absent if the status is "accepted"

   protection                    REQUIRED
       -- As described in Section 3.2
       -- MUST use the same certificate as for protecting the ir

   extraCerts                    RECOMMENDED
       -- As described in Section 3.3
       -- Any certificates in extraCerts MAY be omitted if the message
       -- size is critical and the PKI management entity caches the
       -- extraCerts from the ir

   PKI Confirmation -- pkiconf

   Field                         Value

   header
       -- As described in Section 3.1

   body
     pkiconf                     REQUIRED
       -- The content of this field MUST be NULL

   protection                    REQUIRED
       -- As described in Section 3.2
       -- MUST use the same certificate as for protecting the ip

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   extraCerts                    RECOMMENDED
       -- As described in Section 3.3
       -- Any certificates in extraCerts MAY be omitted if the message
       -- size is critical and the EE has cached the extraCerts from the
       -- ip

4.1.2.  Requesting a certificate from a trusted PKI with signature
        protection

   This PKI management operation should be used by an EE to request an
   additional certificate of the same PKI it already has certificates
   from.  The EE uses one of these existing certificates to authenticate
   itself by signing its request messages using the respective private
   key.

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1.

   Preconditions:

   1  The EE MUST have a certificate enrolled by the PKI it requests
      another certificate from in advance to this PKI management
      operation to authenticate itself to the PKI management entity
      using signature-based protection.

   2  The EE SHOULD know the subject name of the CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of
      the CA, the PKI management entity MUST know where to route this
      request to.

   3  The EE MUST authenticate responses from the PKI management entity;
      trust MAY be established using an enrollment voucher or other
      configuration means.

   4  The PKI management entity MUST trust the current PKI; trust MAY be
      established using some configuration means.

   The message sequence for this PKI management operation is like that
   given in [RFC4210] Appendix D.5.

   The message sequence for this PKI management operation is identical
   to that given in Section 4.1.1, with the following changes:

   1  The body of the first request and response MUST be cr and cp,
      respectively.

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   2  The caPubs field in the cp message SHOULD be absent.

4.1.3.  Updating an existing certificate with signature protection

   This PKI management operation should be used by an EE to request an
   update for one of its certificates that is still valid.  The EE uses
   the certificate it wishes to update to authenticate itself and for
   proving ownership of the certificate to be updated by signing its
   request messages with the corresponding private key.

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1.

   Preconditions:

   1  The certificate the EE wishes to update MUST NOT be expired or
      revoked.

   2  A new public-private key pair SHOULD be used.

   The message sequence for this PKI management operation is like that
   given in [RFC4210] Appendix D.6.

   The message sequence for this PKI management operation is identical
   to that given in Section 4.1.1, with the following changes:

   1  The body of the first request and response MUST be kur and kup,
      respectively.

   2  Protection of the kur MUST be performed using the certificate to
      be updated.

   3  The subject field and/or the subjectAltName extension of the
      CertTemplate MUST contain the EE subject name of the existing
      certificate to be updated, without modifications.

   4  The CertTemplate SHOULD contain the subject and publicKey of the
      EE only.

   5  The oldCertId control SHOULD be used to make clear which
      certificate is to be updated.

   6  The caPubs field in the kup message MUST be absent.

   As part of the certReq structure of the kur the oldCertId control is
   added right after the certTemplate.

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       controls
         type                    RECOMMENDED
       -- MUST be the value id-regCtrl-oldCertID, if present
         value
           issuer                REQUIRED
           serialNumber          REQUIRED
       -- MUST contain the issuer and serialNumber of the certificate
       -- to be updated

4.1.4.  Requesting a certificate from a PKI with MAC protection

   This PKI management operation should be used by an EE to request a
   certificate of a new PKI without having a certificate to prove its
   identity to the target PKI, but there is shared secret information
   established between the EE and the PKI.  Therefore, the
   initialization request is MAC-protected using this shared secret
   information.  The PKI management entity checking the MAC-based
   protection SHOULD replace this protection according to Section 5.1.2
   in case the next hop does not know the shared secret information.

   For requirements regarding proper random number and key generation
   please refer to [RFC4086].

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1.

   Preconditions:

   1  The EE and the PKI management entity MUST share secret
      information, this MAY be established by a service technician
      during initial local configuration.

   2  The EE SHOULD know the subject name of the new CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of
      the CA, the PKI management entity MUST know where to route this
      request to.

   3  The EE MUST authenticate responses from the PKI management entity;
      trust is established using the shared secret information.

   The message sequence for this PKI management operation is like that
   given in [RFC4210] Appendix D.4.

   The message sequence for this PKI management operation is identical
   to that given in Section 4.1.1, with the following changes:

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   1  The protection of all messages MUST be calculated using Message
      Authentication Code (MAC).

   2  The sender MUST contain a name representing the originator of the
      message.  The senderKID MUST contain a reference all participating
      entities can use to identify the shared secret information used
      for the protection, e.g., the username of the EE.

   3  The extraCerts of the ir, certConf, and pkiConf messages MUST be
      absent.

   4  The extraCerts of the ip message MUST contain the chain of the
      issued certificate and root certificates SHOULD not be included
      and MUST NOT be directly trusted in any case.

   See Section 6 of CMP Algorithms [I-D.ietf-lamps-cmp-algorithms] for
   details on message authentication code algorithms (MSG_MAC_ALG) to
   use.  Typically, parameters are part of the protectionAlg structure,
   e.g., used for key derivation, like a salt and an iteration count.
   Such fields SHOULD remain constant for message protection throughout
   this PKI management operation to reduce the computational overhead.

4.1.5.  Requesting a certificate from a legacy PKI using PKCS#10 request

   This PKI management operation can be used by an EE to request a
   certificate using a legacy PKCS#10 [RFC2986] request instead of CRMF
   [RFC4211].  The EE can prove its identity to the target PKI by using
   various protection means as described in Section 4.1.1 or
   Section 4.1.4.

   This operation should be used only for compatibility reasons if the
   other PKI management operations described in Section 4.1 are not
   possible, for instance because a legacy component of the EE only
   produces PKCS#10 requests or a legacy CA system can handle only
   PKCS#10 requests.  In such case the PKI management entity MUST
   extract the PKCS#10 certificate request from the p10cr and provids it
   separately to the CA.

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1, but the public key and all further
   certificate template date is contained in the subjectPKInfo and other
   certificationRequestInfo fields of the PKCS#10 certificate request.

   Preconditions:

   1  The EE MUST either have a certificate enrolled from this or any
      other accepted PKI, or shared secret information known to the PKI
      and the EE to authenticate itself to the RA.

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   2  The EE SHOULD know the subject name of the CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of
      the CA, the RA MUST know where to route this request to.

   3  The EE MUST authenticate responses from the RA; trust MAY be
      established by an available root certificate, using an enrollment
      voucher, or other configuration means.

   4  The addressed PKI management entity MUST trust the PKI the EE uses
      to authenticate itself when using the signature protection; trust
      MAY be established by a corresponding available root certificate
      or using some configuration means.  When using MAC-based
      protection the EE and PKI must share secret information.

   The message sequence for this PKI management operation is identical
   to that given in Section 4.1.1, with the following changes:

   1  The body of the first request and response MUST be p10cr and cp,
      respectively.

   2  The certReqId in the cp message MUST be 0.

   3  The caPubs field in the cp message SHOULD be absent.

   Detailed description of the p10cr message:

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   Certification Request -- p10cr

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The request of the EE for a new certificate using a PKCS#10
       -- certificate request
     p10cr                       REQUIRED
       certificationRequestInfo  REQUIRED
         version                 REQUIRED
       -- MUST be set to 0 to indicate PKCS#10 V1.7
         subject                 REQUIRED
       -- The EE subject name MUST be carried in the subject field
       -- and/or the subjectAltName extension.
       -- If subject name is present only in the subjectAltName
       -- extension, then the subject field MUST be a NULL-DN
         subjectPKInfo           REQUIRED
           algorithm             REQUIRED
       -- MUST include the subject public key algorithm ID
           subjectPublicKey      REQUIRED
       -- MUST include the public key to be certified
         attributes              OPTIONAL
       -- MAY include end-entity-specific X.509 extensions of the
       -- requested certificate like subject alternative name,
       -- key usage, and extended key usage.
       -- The subjectAltName extension MUST be present if the EE
          -- subject name includes a subject alternative name.
       signatureAlgorithm        REQUIRED
       -- The signature algorithm MUST be consistent with the
       -- subjectPKInfo field.
       signature                 REQUIRED
       -- MUST containing the self-signature for proof-of-possession

   protection                    REQUIRED
       -- As described in Section 3.2

   extraCerts                    REQUIRED
       -- As described in Section 3.3

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4.1.6.  Generateing the key pair centrally at the PKI management entity

   This functional extension can be applied in combination with
   certificate enrollment as described in Section 4.1.1, Section 4.1.2,
   and Section 4.1.4.  The functional extension can be used in case an
   EE is not able to generate its new public-private key pair itself or
   central generation the EE key material is preferred.  It is a matter
   of the local implementation which PKI management entity will act as
   Key Generation Authority (KGA) and perform the key generation.  This
   PKI management entity MUST have a certificate containing the
   additional extended key usage extension id-kp-cmKGA in order to be
   accepted by the EE as a legitimate key generation authority.  The KGA
   can use one of the PKI management operations described in the
   sections above to request the certificate for this key pair on behalf
   of the EE.

   Generally speaking, in machine-to-machine scenarios it is strongly
   preferable to generate public-private key pairs locally at the EE.
   Together with proof-of-possession of the private key in the
   certification request, this helps a lot to make sure that the entity
   identified in the newly issued certificate is the only entity that
   knows the private key.

   Reasons for central key generation may include the following:

   *  Lack of sufficient initial entropy.

   Note: Good random numbers are needed not only for key generation but
   also for session keys and nonces in any security protocol.
   Therefore, a decent security architecture should anyways support good
   random number generation on the EE side or provide enough initial
   entropy for the RNG seed to guarantee good pseudo-random number
   generation.  Yet maybe this is not the case at the time of requesting
   an initial certificate during manufacturing.

   *  Lack of computational resources, e.g., in case of RSA key
      generation.

   Note: Since key generation could be performed in advance to the
   certificate enrollment communication, it is often not time critical.

   Note: As mentioned in Section 2.1 central key generation may be
   required in a push model, where the certificate response message is
   transferred by the PKI management entity to the EE without a previous
   request message.

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   If the EE wishes to request central key generation, it MUST fill the
   subjectPublicKey field in the certTemplate structure of the request
   message with a zero-length BIT STRING.  This indicates to the PKI
   management entity that a new key pair shall be generated centrally on
   behalf of the EE.

   Note: As the protection of centrally generated keys in the response
   message is being extended from EncryptedValue to EncryptedKey by CMP
   Updates [I-D.ietf-lamps-cmp-updates], also the alternative
   EnvelopedData can be used.  In CRMF Section 2.1.9 [RFC4211] the use
   of EncryptedValue has been deprecated in favor of the EnvelopedData
   structure.  Therefore, this profile requires using EnvelopedData as
   specified in CMS Section 6 [RFC5652].  When EnvelopedData is to be
   used in a transaction, CMP V3 MUST be indicated in the message
   header, see CMP Updates [I-D.ietf-lamps-cmp-updates].

                   +----------------------------------+
                   | EnvelopedData                    |
                   | [RFC5652] section 6              |
                   | +------------------------------+ |
                   | | SignedData                   | |
                   | | [RFC5652] section 5          | |
                   | | +--------------------------+ | |
                   | | | AsymmetricKeyPackage     | | |
                   | | | [RFC5958]                | | |
                   | | | +----------------------+ | | |
                   | | | | privateKey           | | | |
                   | | | | OCTET STRING         | | | |
                   | | | +----------------------+ | | |
                   | | +--------------------------+ | |
                   | +------------------------------+ |
                   +----------------------------------+

                 Figure 3: Encrypted private key container

   The PKI management entity delivers the private key in the privateKey
   field in the certifiedKeyPair structure of the response message also
   containing the newly issued certificate.

   The private key MUST be provided as an AsymmetricKeyPackage structure
   as defined in RFC 5958 [RFC5958].

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   This AsymmetricKeyPackage structure MUST be wrapped in a SignedData
   structure, as specified in CMS Section 5 [RFC5652], signed by the KGA
   generating the key pair.  The signature MUST be performed using a
   private key related to a certificate asserting the extended key usage
   kp-id-cmKGA as described in CMP Updates [I-D.ietf-lamps-cmp-updates]
   in order to show the authorization to generate key pairs on behalf of
   an EE.

   Note: When of using password-based key management technique as
   described in Section 4.1.6.3 it may not be possible or meaningful to
   the EE to validate the KGA signature in the SignedData structure
   since shared secret information is used for initial authentication.
   In this case the EE MAY omit this signature validation.

   This SignedData structure MUST be wrapped in an EnvelopedData
   structure, as specified in CMS Section 6 [RFC5652], encrypting it
   using a newly generated symmetric content-encryption key.

   This content-encryption key MUST be securely provided as part of the
   EnvelopedData structure to the EE using one of three key management
   techniques.  The choice of the key management technique to be used by
   the PKI management entity depends on the authentication mechanism the
   EE choose to protect the request message.  See CMP Updates section
   3.4 [I-D.ietf-lamps-cmp-updates] for more details on which key
   management technique to use.

   *  Signature-protected request message:

      -  The content-encryption key SHALL be protected using the key
         agreement key management technique, see Section 4.1.6.1, if the
         certificate used by the EE for protecting the request message
         allows the key usage keyAgreement.  If the certificate also
         allows the key usage keyEncipherment, the key transport key
         management technique SHALL NOT be used.

      -  The content-encryption key SHALL be protected using the key
         transport key management technique, see Section 4.1.6.2, if the
         certificate used by the EE for protecting the respective
         request message allows the key usage keyEncipherment but not
         keyAgreement.

   *  MAC-protected request message:

      -  The content-encryption key SHALL be protected using the
         password-based key management technique, see Section 4.1.6.3,
         if and only if the EE used MAC protection for the request
         message.

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   If central key generation is supported, support of the key agreement
   key management technique is REQUIRED and support of key transport and
   password-based key management techniques are OPTIONAL.  This is due
   to two reasons: The key agreement key management technique is
   supported by most asymmetric algorithms, while the key transport key
   management technique is supported only by a very few asymmetric
   algorithms.  And as mentioned the password-based key management
   technique shall only be used in combination with MAC protection,
   which is a sideline in this document.

   For details on algorithms to be used, please see CMP Algorithms
   Section 4 and 5 [I-D.ietf-lamps-cmp-algorithms].

   For encrypting the SignedData structure containing the private key a
   fresh content-encryption key MUST be generated with sufficient
   entropy for the symmetric encryption algorithm used.

   Note: Depending on the lifetime of the certificate and the
   criticality of the generated private key, it is advisable to use the
   strongest available symmetric encryption algorithm.

   The detailed description of the privateKey field as follows:

           privateKey            OPTIONAL
       -- MUST be an EnvelopedData structure as specified in
       -- CMS [RFC5652] section 6
             version             REQUIRED
       -- MUST be set to 2 for recipientInfo type KeyAgreeRecipientInfo
       -- and KeyTransRecipientInfo
       -- MUST be set to 0 for recipientInfo type PasswordRecipientInfo
             recipientInfos      REQUIRED
       -- MUST be exactly one RecipientInfo
               recipientInfo     REQUIRED
       -- MUST be either KeyAgreeRecipientInfo (see section 4.1.6.1),
       -- KeyTransRecipientInfo (see section 4.1.6.2), or
       -- PasswordRecipientInfo (see section 4.1.6.3)
       -- If central key generation is supported, support of
       -- KeyAgreeRecipientInfo is REQUIRED and support of
       -- KeyTransRecipientInfo and PasswordRecipientInfo are OPTIONAL
             encryptedContentInfo
                                 REQUIRED
               contentType       REQUIRED
       -- MUST be id-signedData
               contentEncryptionAlgorithm
                                 REQUIRED
       -- MUST specify the algorithm OID of the algorithm used for
       -- content encryption
       -- The algorithm MUST be a PROT_SYM_ALG as specified in

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       -- RFC-CMP-Alg Section 5
               encryptedContent  REQUIRED
       -- MUST be the SignedData structure as specified in
       -- CMS Section 5 [RFC5652] in encrypted form
                 version         REQUIRED
       -- MUST be set to 3 if X.509 V3 certificates are included
                 digestAlgorithms
                                 REQUIRED
       -- MUST be exactly one digestAlgorithm OID
                   digestAlgorithmIdentifier
                                 REQUIRED
       -- MUST be the OID of the digest algorithm used for generating
       -- the signature and match the signature algorithm specified in
       -- signatureAlgorithm
                 encapContentInfo
                                 REQUIRED
       -- MUST contain the content that is to be signed
                   eContentType   REQUIRED
       -- MUST be id-ct-KP-aKeyPackage as specified in [RFC5958]
                   eContent       REQUIRED
                     AsymmetricKeyPackage
                                 REQUIRED
       -- MUST contain exactly one OneAsymmetricKey element
                       OneAsymmetricKey
                                 REQUIRED
                         version REQUIRED
       -- MUST be set to 1
                         privateKeyAlgorithm
                                 REQUIRED
       -- The privateKeyAlgorithm field MUST contain
       -- the OID of the asymmetric key pair algorithm
                         privateKey
                                 REQUIRED
       -- MUST contain the new private key
                         attributes
                                 OPTIONAL
       -- The attributes field SHOULD not be used
                         publicKey
                                 REQUIRED
       -- MUST contain the public key corresponding to the private key
       -- for simplicity and consistency with V2 of OneAsymmetricKey
                 certificates    REQUIRED
       -- SHOULD contain the certificate, for the private key used
       -- to sign the content, together with its chain
       -- If present, the first certificate in this field MUST
       -- be the certificate used for protecting this content
       -- Self-signed certificates SHOULD NOT be included
       -- and MUST NOT be trusted based on their inclusion in any case

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                 crls            OPTIONAL
       -- MAY be present to provide status information on the protection
       -- certificate or its CA certificates
                 signerInfos     REQUIRED
       -- MUST be exactly one signerInfo
                   version       REQUIRED
       -- MUST be set to 3
                   sid           REQUIRED
                     subjectKeyIdentifier
                                 REQUIRED
       -- MUST be the subjectKeyIdentifier of the protection certificate
                   digestAlgorithm
                                 REQUIRED
       -- MUST be the same as in digestAlgorithmIdentifier
                   signedAttrs   REQUIRED
       -- MUST contain an id-contentType attribute containing the same
       -- value as eContentType
       -- MUST contain an id-messageDigest attribute containing the
       -- message digest of eContent
       -- MAY contain an id-signingTime attribute containing the time of
       -- signature
       -- For details on the signed attributes see CMS Section 5.3
       -- and Section 11 [RFC5652]
                   signatureAlgorithm
                                 REQUIRED
       -- MUST be the algorithm OID of the signature algorithm used for
       -- calculation of the signature bits
       -- The signature algorithm MUST be a MSG_SIG_ALG as specified in
       -- RFC-CMP-Alg Section 3 and MUST be consistent with the
       -- subjectPublicKeyInfo field of the CMP KGA certificate
                   signature     REQUIRED
       -- MUST be the result of the digital signature generation

   NOTE: As defined in Section 1.5 any field of the ASN.1 syntax as
   defined in RFC 5652 [RFC5652] not explicitly specified here, SHOULD
   NOT be used by the sending entity.

4.1.6.1.  Using key agreement key management technique

   This key management technique can be applied in combination with the
   PKI management operations specified in Section 4.1.1 to Section 4.1.3
   using signature-based protected CMP messages.  The public key of the
   EE certificate used for the signature-based protection of the request
   message MUST also be used for the key establishment of the content-
   encryption key.  To use this key management technique the
   KeyAgreeRecipientInfo structure MUST be used in the contentInfo
   field.

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   The KeyAgreeRecipientInfo structure included into the EnvelopedData
   structure is specified in CMS Section 6.2.2 [RFC5652].

   The detailed description of the KeyAgreeRecipientInfo structure looks
   like this:

               recipientInfo     REQUIRED
       -- MUST be KeyAgreeRecipientInfo as specified in
                 version         REQUIRED
       -- MUST be set to 3
                 originator      REQUIRED
       -- MUST contain the originatorKey choice
                   algorithm     REQUIRED
       -- MUST be the algorithm OID of the key agreement algorithm
       -- The algorithm MUST be a KM_KA_ALG as specified in
       -- RFC-CMP-Alg Section 4.1
                   publicKey     REQUIRED
       -- MUST be the ephemeral public key of the sending party
                 ukm             RECOMMENDED
       -- MUST be used when 1-pass ECMQV is used
       -- SHOULD be present to ensure uniqueness of the key
       -- encryption key, see [RFC8419]
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST be the algorithm OID of the key wrap algorithm
       -- The algorithm MUST be a KM_KW_ALG as specified in
       -- RFC-CMP-Alg Section 4.3
                 recipientEncryptedKeys
                                 REQUIRED
       -- MUST contain exactly one RecipientEncryptedKey element
                     rid         REQUIRED
       -- MUST contain the rKeyId choice
                       rKeyId    REQUIRED
                         subjectKeyIdentifier
                                 REQUIRED
       -- MUST contain the same value as the senderKID in the
       -- respective request messages
                     encryptedKey
                                 REQUIRED
       -- MUST be the encrypted content-encryption key

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4.1.6.2.  Using key transport key management technique

   This key management technique can be applied in combination with the
   PKI management operations specified in Section 4.1.1 to Section 4.1.3
   using signature-based protected CMP messages.  The public key of the
   EE certificate used for the signature-based protection of the request
   message MUST also be used for key encipherment of the content-
   encryption key.  To use this key management technique the
   KeyTransRecipientInfo structure MUST be used in the contentInfo
   field.

   The KeyTransRecipientInfo structure included into the EnvelopedData
   structure is specified in CMS Section 6.2.1 [RFC5652].

   The detailed description of the KeyTransRecipientInfo structure looks
   like this:

               recipientInfo     REQUIRED
       -- MUST be KeyTransRecipientInfo as specified in
       -- CMS section 6.2.1 [RFC5652]
                 version         REQUIRED
       -- MUST be set to 2
                 rid             REQUIRED
          -- MUST contain the subjectKeyIdentifier choice
                   subjectKeyIdentifier
                                 REQUIRED
       -- MUST contain the same value as the senderKID in the respective
       -- request messages
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST be the algorithm OID of the key transport algorithm
       -- The algorithm MUST be a KM_KT_ALG as specified in RFC-CMP-Alg
       -- Section 4.2
                 encryptedKey    REQUIRED
       -- MUST be the encrypted content-encryption key

4.1.6.3.  Using password-based key management technique

   This key management technique can be applied in combination with the
   PKI management operation specified in Section 4.1.4 using MAC-based
   protected CMP messages.  The shared secret information used for the
   MAC-based protection MUST also be used for the encryption of the
   content-encryption key but with a different salt value applied in the
   key derivation algorithm as used for the MAC-based protection . To
   use this key management technique the PasswordRecipientInfo structure
   MUST be used in the contentInfo field.

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   The PasswordRecipientInfo structure included into the EnvelopedData
   structure is specified in CMS Section 6.2.4 [RFC5652].

   The detailed description of the PasswordRecipientInfo structure looks
   like this:

               recipientInfo     REQUIRED
       -- MUST be PasswordRecipientInfo as specified in
       -- CMS section 6.2.4 [RFC5652]
                 version         REQUIRED
       -- MUST be set to 0
                 keyDerivationAlgorithm
                                 REQUIRED
       -- MUST be the algorithm OID of the key derivation algorithm
       -- The algorithm MUST be a KM_KD_ALG as specified in RFC-CMP-Alg
       -- Section 4.4
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST be the algorithm OID of the key wrap algorithm
       -- The algorithm MUST be a KM_KW_ALG as specified in RFC-CMP-Alg
       -- Section 4.3
                 encryptedKey    REQUIRED
       -- MUST be the encrypted content-encryption key

4.1.7.  Delayed enrollment

   This functional extension can be applied in combination with
   certificate enrollment as described in Section 4.1.1 to
   Section 4.1.5.  The functional extension can be used in case a PKI
   management entity cannot respond to the certificate request in a
   timely manner, e.g., due to offline upstream communication or
   required registration officer interaction.  Depending on the PKI
   architecture, the entity initiating delayed enrollment is not
   necessarily the PKI management entity directly addressed by the EE.

   Note: According to CMP Updates [I-D.ietf-lamps-cmp-updates] polling
   is also possible for PKI management operations starting with a p10cr
   request message.

   The PKI management entity initiating the delayed enrollment MUST
   respond with an ip/cp/kup message including the status "waiting".
   When receiving a response with status "waiting" the EE MUST send a
   poll request to the same PKI management entity as before.  The PKI
   management entity that initiated the delayed enrollment MUST answer
   with a poll response containing a checkAfter time.  This value
   indicates the minimum number of seconds that should elapse before the
   EE sends another poll request.  This is repeated as long as no final
   response is available or any party involved gives up on the current

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   transaction.  When the PKI management entity that initiated delayed
   enrollment can provide the final ip/cp/kup message for the initial
   request of the EE, it MUST provide this message in response to a poll
   request.  After receiving this response, the EE can continue the
   original PKI management operation as described in the respective
   section of this document, e.g., sending a certConf message.

   Message flow:

   Step# EE                                   PKI management entity
    1   format ir/cr/p10cr/kur
        As described in the
          respective section
          in this document
    2                    ->ir/cr/p10cr/kur->
    3                                        handle request as described
                                               in the respective section
                                               in this document
    4                                        in case no immediate final
                                               response is possible,
                                               receive or format ip, cp
                                               or kup message containing
                                               status "waiting"
    5                      <-  ip/cp/kup  <-
    6   handle ip/cp/kup with status "waiting"
    7   format pollReq
    8                      ->   pollReq   ->
    9                                        handle, re-protect or
                                               forward pollReq
   10                                        in case the requested
                                               certificate or a
                                               corresponding response
                                               message is available,
                                               receive or format ip, cp,
                                               or kup containing the
                                               issued certificate, else
                                             format or receive pollRep
                                               with appropriate
                                               checkAfter value
   11                      <-   pollRep   <-
   12   handle pollRep
   13   let checkAfter
          time elapse
   14   continue with line 7

   Detailed description of the first ip/cp/kup:

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   Response with status 'waiting'  -- ip/cp/kup

   Field                         Value

   header
       -- MUST contain a header as described for the first response
       -- message of the respective PKI management operation

   body
       -- The response of the PKI management entity to the request in
       -- case no immediate appropriate response can be sent
     ip/cp/kup                   REQUIRED
       response                  REQUIRED
       -- MUST contain exactly one CertResponse
         certReqId               REQUIRED
       -- MUST be 0
         status                  REQUIRED
       -- PKIStatusInfo structure MUST be present
           status                REQUIRED
       -- MUST be "waiting"
           statusString          OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI
           failInfo              PROHIBITED
         certifiedKeyPair        PROHIBITED

   protection                    REQUIRED
       -- MUST contain protection as described for the first response
       -- message of the respective PKI management operation, except
       -- that the PKI management entity that initiated the delayed
       -- enrollment and created this response MUST apply its own
       -- protection

   extraCerts                    REQUIRED
       -- MUST contain certificates as described for the first response
       -- message of the respective PKI management operation. Yet since
       -- no new certificate is included yet, no respective certificate
       -- chain is included

   Polling Request -- pollReq

   Field                         Value

   header
       -- MUST contain a header as described for the certConf message
       -- of the respective PKI management operation

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   body
       -- The message of the EE asks for the final response or for a
       -- time to check again
     pollReq                     REQUIRED
       -- MUST contain exactly one element
       certReqId                 REQUIRED
       -- MUST be 0

   protection                    REQUIRED
       -- MUST contain protection as described for the certConf message
       -- of the respective PKI management operation

   extraCerts                    OPTIONAL
       -- MUST be as described for the certConf message of the
       -- respective PKI management operation

   Polling Response -- pollRep

   Field                         Value

   header
       -- MUST contain a header as described for the pkiConf message
       -- of the respective PKI management operation

   body
       -- The message indicates the delay after which the EE may send
       -- another pollReq message for this transaction
     pollRep                     REQUIRED
       -- MUST contain exactly one entry
       certReqId                 REQUIRED
       -- MUST be 0
       checkAfter                REQUIRED
       -- time in seconds to elapse before a new pollReq should be sent
       reason                    OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI

   protection                    REQUIRED
       -- MUST contain protection as described for the pkiConf message
       -- of the respective profile, except that the PKI management
       -- entity that initiated the delayed enrollment and created this
       -- response MUST apply its own protection

   extraCerts                    OPTIONAL
       -- If present, it MUST contain certificates as described for the
       -- pkiConf message of the respective PKI management operation.

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   Final response -- ip/cp/kup

   Field                         Value

   header
       -- MUST contain a header as described for the first
       -- except that the PKI management entity that initiated the
       -- delayed enrollment MUST replace the recipNonce by be the
       -- senderNonce of the last pollReq message

   body
       -- The response of the PKI management entity to the initial
       -- request as described in the respective PKI management
       -- operation

   protection                    REQUIRED
       -- MUST contain protection as described for the first response
       -- message of the respective PKI management operation, except
       -- that the PKI management entity that initiated the delayed
       -- enrollment MUST re-protect the response message

   extraCerts                    REQUIRED
       -- MUST contain certificates as described for the first
       -- response message of the respective PKI management operation

4.2.  Revoking a certificate

   This PKI management operation should be used by an entity to request
   revocation of a certificate.  Here the revocation request is used by
   an EE to revoke one of its own certificates.  A PKI management entity
   could also act as an EE to revoke one of its own certificates.

   The revocation request message MUST be signed using the certificate
   that is to be revoked to prove the authorization to revoke.  The
   revocation request message is signature-protected using this
   certificate.

   An EE requests the revocation of an own certificate at the CA that
   issued this certificate.  The PKI management entity responds with a
   message that contains the status of the revocation from the CA.

   Preconditions:

   1  The certificate the EE wishes to revoke is not yet expired or
      revoked.

   Message flow:

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   Step# EE                                  PKI management entity
     1   format rr
     2                      ->   rr      ->
     3                                        handle, re-protect or
                                                forward rr
     4                                        format or receive rp
     5                      <-   rp      <-
     6   handle rp

   For this PKI management operation, the EE MUST include exactly one
   RevDetails structure in the rr message body.  In case no error
   occurred the response to the rr MUST be an rp message containing a
   status field with a single set of values.

   Detailed message description:

   Revocation Request -- rr

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The request of the EE to revoke its certificate
     rr                          REQUIRED
       -- MUST contain exactly one element of type RevDetails
       -- If more revocations are desired, further requests MUST be
       -- packaged in separate PKI Messages
       certDetails               REQUIRED
       -- MUST be present and be of type CertTemplate
         serialNumber            REQUIRED
       -- MUST contain the certificate serialNumber attribute of the
       -- X.509 certificate to be revoked
         issuer                  REQUIRED
       -- MUST contain the issuer attribute of the X.509 certificate to
       -- be revoked
       crlEntryDetails           REQUIRED
       -- MUST contain exactly one reasonCode of type CRLReason (see
       -- [RFC5280] section 5.3.1)
       -- If the reason for this revocation is not known or shall not be
       -- published the reasonCode MUST be 0 = unspecified

   protection                    REQUIRED
       -- As described in Section 3.2 and using the private key related
       -- to the certificate to be revoked

   extraCerts                    REQUIRED

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       -- As described in Section 3.3

   Revocation Response -- rp

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The responds of the PKI management entity to the request as
       -- appropriate
     rp                          REQUIRED
       status                    REQUIRED
       -- MUST contain exactly one element of type PKIStatusInfo
         status                  REQUIRED
       -- positive value allowed: "accepted"
       -- negative value allowed: "rejection"
         statusString            OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI
         failInfo                OPTIONAL
       -- MAY be present if and only if status is "rejection"

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    REQUIRED
       -- As described in section 3.3

4.3.  Error reporting

   This functionality should be used by an EE to report error conditions
   upstream to the PKI management entity such that the involved PKI
   management entities can immediately free their resources related to
   the current transaction.  Error reporting by a PKI management entity
   downstream to the EE is described in Section 5.3.

   In case the error condition is related to specific details of an ip,
   cp, or kup response message and a confirmation is expected the error
   condition MUST be reported in the respective certConf message with
   negative contents.

   General error conditions, e.g., problems with the message header,
   protection, or extraCerts, and negative feedback on rp, pollRep, or
   pkiConf messages MUST be reported in the form of an error message.

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   In both situations the EE reports the status "rejection" in the
   PKIStatusInfo structure of the respective message.

   Depending on the PKI architecture, the addressed PKI management
   entity MUST forward the error message (upstream) to the next PKI
   management entity and MUST terminate this PKI management operation on
   receiving any response.

   The PKIStatusInfo structure is used to report errors.  The
   PKIStatusInfo structure consists of the following fields:

   *  status: Here the PKIStatus value "rejection" is the only one
      allowed.

   *  statusString: Here any human-readable valid value for logging or
      to display in a GUI SHOULD be added.

   *  failInfo: Here the PKIFailureInfo values MAY be used in the way
      explained in Appendix F of RFC 4210 [RFC4210].  The following
      PKIFailureInfo values have specific usage and therefore are
      described in detail here:

      -  transactionIdInUse: This is sent by a PKI management entity in
         case the received request contains a transaction ID that has
         already been used for another transaction.  An EE receiving
         such error message SHOULD resend the request in a new
         transaction using a different transaction ID.

      -  systemUnavail or systemFailure: This is sent by a PKI
         management entity in case a back-end system is not available or
         currently not functioning correctly.  An EE receiving such
         error message SHOULD resend the request in a new transaction
         after some time.

   Detailed error message description:

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   Error Message -- error

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The message sent by the EE or the (L)RA/CA to indicate an
       -- error that occurred
     error                       REQUIRED
       pKIStatusInfo             REQUIRED
         status                  REQUIRED
       -- MUST have the value "rejection"
         statusString            RECOMMENDED
       -- SHOULD be any human-readable text for debugging, logging
       -- or to display in a GUI
         failInfo                OPTIONAL
       -- MAY be present

   protection                    REQUIRED
       -- As described in Section 3.2

   extraCerts                    OPTIONAL
       -- As described in Section 3.3

4.4.  Support messages

   The following support messages offer on demand in-band transport of
   content relevant to the EE that may be provided by the PKI management
   entity.  CMP general messages and general response are used for this
   purpose.  Depending on the environment, these requests may be
   answered by an LRA, RA, or CA.

   The general messages and general response messages transport
   InfoTypeAndValue structures.  In addition to those infoType values
   defined in RFC 4210 [RFC4210] further OIDs MAY be used to define new
   PKI management operations or new general-purpose support messages as
   needed in specific environments.

   The following contents are specified in this document:

   *  Get CA certificates

   *  Get root CA certificate updates

   *  PGet certificate request templates

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   The PKI management operation is similar to that given in Appendix E.5
   of RFC 4210 [RFC4210].  In this section the aspects common to all
   general messages (genm) and to all general responses (genp) are
   described.

   The behavior in case an error occurs is described in Section 4.3.

   Message flow:

   Step# EE                                   PKI management entity
    1   format genm
    2                      ->   genm    ->
    3                                        handle, re-protect or
                                               forward genm
    4                                        format or receive genp
    5                      <-   genp    <-
    6   handle genp

   Detailed message description:

   General Message -- genm

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- A request by the EE to receive information
     genm                        REQUIRED
       -- MUST contain exactly one element of type
       -- InfoTypeAndValue
       infoType                  REQUIRED
       -- MUST be the OID identifying the specific PKI
       -- management operation described below
       infoValue                 OPTIONAL
       -- MUST be as described in the specific PKI
       -- management operation described below

   protection                    REQUIRED
       -- As described in Section 3.2

   extraCerts                    REQUIRED
       -- As described in Section 3.3

   General Response -- genp

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   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- The response of the PKI management entity to an
       -- information request
     genp                        REQUIRED
       -- MUST contain exactly one element of type
       -- InfoTypeAndValue
       infoType                  REQUIRED
       -- MUST be the OID identifying the specific PKI
       -- management operation described below
       infoValue                 OPTIONAL
       -- MUST be as described in the specific PKI
       -- management operation described below

   protection                    REQUIRED
       -- As described in Section 3.2

   extraCerts                    REQUIRED
       -- As described in Section 3.3

4.4.1.  Get CA certificates

   This PKI management operation can be used by an EE to request CA
   certificates from the PKI management entity.

   An EE requests CA certificates from the PKI management entity by
   sending a general message with OID id-it-caCerts as specified in CMP
   Updates [I-D.ietf-lamps-cmp-updates].  The PKI management entity
   responds with a general response with the same OID that either
   contains a SEQUENCE of certificates populated with the available CA
   intermediate and issuing CA certificates or with no content in case
   no CA certificate is available.

   The message sequence for this PKI management operation is as given in
   Section 4.4, with the following specific content:

   1  the body MUST contain as infoType the OID id-it-caCerts

   2  the infoValue of the request MUST be absent

   3  if present, the infoValue of the response MUST contain a sequence
      of certificates

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   The infoValue field of the general response containing the id-it-
   caCerts OID looks like this:

         infoValue               OPTIONAL
       -- MUST be absent if no CA certificate is available
       -- MUST be present if CA certificates are available
       -- MUST be a sequence of CMPCertificate

4.4.2.  Get root CA certificate update

   This PKI management operation can be used by an EE to retrieve any
   updated root CA Certificate as described in Section 4.4 of RFC 4210
   [RFC4210].

   An EE requests a root CA certificate update from the PKI management
   entity by sending a general message with OID id-it-rootCaKeyUpdate as
   specified in CMP Updates [I-D.ietf-lamps-cmp-updates].  The PKI
   management entity responds with a general response with the same OID
   that either contains the update of the root CA certificate consisting
   of up to three certificates, or with no content in case no update is
   available.

   The newWithNew certificate is the new root CA certificate and is
   REQUIRED to be present in the response message.  The newWithOld
   certificate is RECOMMENDED to be present in the response message,
   because it is needed for those cases where the receiving entity
   trusts the old root CA certificate and wishes to gain trust in the
   new root CA certificate.  It MAY be omitted if the PKI management
   entity that performed the message protection of the response message
   is authorization to update the trust store of the EE.  The oldWithNew
   certificate is OPTIONAL, because it is only needed in a scenario
   where the requesting entity does not have an own certificate under
   the new root CA and wishes to authenticate to entities not trusting
   the old root CA.

   The message sequence for this PKI management operation is as given in
   Section 4.4, with the following specific content:

   1  the body MUST contain as infoType the OID id-it-rootCaKeyUpdate

   2  the infoValue of the request MUST be absent

   3  if present, the infoValue of the response MUST be a
      RootCaKeyUpdate structure

   The infoValue field of the general response containing the id-it-
   rootCaKeyUpdate extension looks like this:

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         infoValue               OPTIONAL
       -- MUST be absent if no update of the root CA certificate is
       -- available
       -- MUST be present if an update of the root CA certificate
       -- is available and MUST be of type RootCaKeyUpdate
           newWithNew            REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the new root CA certificate
           newWithOld            RECOMMENDED
       -- SHOULD be present if infoValue is present
       -- MUST contain a certificate containing the new public
       -- root CA key signed with the old private root CA key
           oldWithNew            OPTIONAL
       -- MAY be present if infoValue is present
       -- MUST contain a certificate containing the old public
       -- root CA key signed with the new private root CA key

   < TBD: In case the PKI management entity serves for more than one
   Root CA.  There are three different options to handle this: - The EE
   specifies by means of a respective label in the HTTP endpoint for
   which Root CA certificate the update is requested. - The EE transfers
   the oldWithOld certificate or its S/N+issuer in the InfoValue of the
   request. - The PKI management entity provides several
   InfoTypeAndValue pairs in the response containing a RootCaKeyUpdate
   element for each Root CA where an update is available. >

4.4.3.  Get certificate request template

   This PKI management operation can be used by an EE to request a
   template with parameters for a future certificate requests.

   An EE requests certificate request parameters from the PKI management
   entity by sending a general message with OID id-it-certReqTemplate as
   specified in CMP Updates [I-D.ietf-lamps-cmp-updates].  The PKI
   management entity responds with a general response with the same OID
   that either contains a certificate template containing requirements
   on certificate fields and extensions and optionally a keySpec field
   containing requirements on algorithms acceptable for key pair
   generation, or with no content in case no specific requirements are
   imposed by the PKI.

   The EE SHOULD follow the requirements from the received CertTemplate
   and the optional keySpec field, by including in the certTemplate of
   certificate requests all the fields requested, taking over all the
   field values provided and filling in any remaining fields values.
   The EE SHOULD NOT add further CertTemplate fields, Name components,
   and extensions or their (sub-)components.

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   Note: We deliberately do not use 'MUST' or 'MUST NOT' here in order
   to allow more flexibility in case the rules given here are not
   sufficient for specific scenarios.  The EE can populate the
   certificate request as wanted and ignore any of the requirements
   contained in the CertReqTemplate response message.  On the other
   hand, a PKI management entity is free to ignore or replace any parts
   of the content of the certificate request provided by the EE.  The
   CertReqTemplate PKI management operation offers means to ease a joint
   understanding which fields and/or which field values should be used.

   In case a field of type Name, e.g., issuer or subject, is present in
   the CertTemplate but has the value NULL-DN (i.e., has an empty list
   of RDN components) the field SHOULD be included in the certTemplate
   and filled with content provided by the EE.  Similarly, in case an
   X.509v3 extension is present but its extnValue is empty this means
   that the extension SHOULD be included and filled with content
   provided by the EE.  In case a Name component, for instance a common
   name or serial number, is given but has an empty string value the EE
   SHOULD fill in a value.  Similarly, in case an extension has sub-
   components (e.g., an IP address in a SubjectAltName field) with empty
   value, the EE SHOULD fill in a value.

   The EE MUST ignore (i.e., not include and fill in) empty fields,
   extensions, and sub-components that it does not understand or does
   not know suitable values to be filled in.

   The publicKey field of type SubjectPublicKeyInfo in the CertTemplate
   MUST be omitted.  In case the PKI management entity wishes to make
   stipulation on supported algorithms the EE may use for key
   generation, this MUST be specified using the control fields as
   specified in CMP Updates [I-D.ietf-lamps-cmp-updates].

   The keySpec field, if present, specifies the public key types and
   lengths for which a certificate may be requested.

   The value of a keySpec with the OID id-regCtrl-algId, as specified in
   CMP Updates [I-D.ietf-lamps-cmp-updates], MUST be of type
   AlgorithmIdentitier and gives an algorithm other than RSA.  For EC
   keys the full curve information MUST be specified as described in the
   respective standard documents.

   The value of a keySpec with the OID id-regCtrl-rsaKeyLen, as
   specified in CMP Updates [I-D.ietf-lamps-cmp-updates], MUST be of
   type Integer and gives an RSA key length.

   The PKI management entity responds with a general response with the
   same OID that either contains a certificate template containing
   requirements on certificate fields and extensions and optionally a

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   keySpec field containing requirements on algorithms acceptable for
   key pair generation, or with no content in case no specific
   requirements are imposed by the PKI.

   The EE SHOULD follow the requirements from the received CertTemplate
   and the optional keySpec field, by including in the certTemplate of
   certificate requests all the fields requested, taking over all the
   field values provided and filling in any remaining fields values.
   The EE SHOULD NOT add further CertTemplate fields, name components,
   and extensions or their (sub-)components.  In case several keySpec
   elements are present the EE can choose one of the specified
   algorithms for key pair generation.  In case the keySpec field is
   absent the EE is free to choose any public key type including
   parameters.

   In the CertTemplate structure the serialNumber, signingAlg,
   publicKey, issuerUID, and subjectUID fields MUST be omitted.

   The message sequence for this PKI management operation is as given in
   Section 4.4, with the following specific content:

   1  the body MUST contain as infoType the OID id-it-certReqTemplate

   2  the infoValue of the request MUST be absent

   3  if present, the infoValue of the response MUST be a CertTemplate
      structure and an optional SEQUENCE of AttributeTypeAndValue with
      attribute type id-regCtrl-algId or id-regCtrl-rsaKeyLen

   The infoValue field of the general response containing the id-it-
   certReqTemplate OID looks like this:

         InfoValue               OPTIONAL
       -- MUST be absent if no requirements are available
       -- MUST be present if the PKI management entity has any
       -- requirements on the content of the certificates template
           certTemplate          REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the prefilled CertTemplate structure elements
       -- The SubjectPublicKeyInfo MUST contain no algorithm ID i.e.,
       -- the null OBJECT IDENTIFIER) in the algorithm field and a
       -- zero-length BIT STRING in the subjectPublicKey field
           keySpec               OPTIONAL
       -- MUST be absent if no requirements on the public key are
       -- available MUST be present if the PKI management entity has any
       -- requirements on the key generation
       -- MUST contain one AttributeTypeAndValue per supported algorithm
       -- with attribute id-regCtrl-algId or id-regCtrl-rsaKeyLen

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   < TBD: In case the PKI management entity offers for more than one set
   of certificate request parameters.  There are three different options
   to handle this: - The EE specifies by means of a respective label in
   the HTTP endpoint for which set of certificate request parameters is
   requested the template. - The EE neame of the set of certificate
   request parameters in the InfoValue of the request. - The PKI
   management entity provides several InfoTypeAndValue pairs in the
   response containing a set of certificate request parameter in each
   InfoTypeAndValue pairs. >

5.  LRA and RA PKI management operations

   This section focuses on the communication among PKI management
   entities.  Depending on the network and PKI solution design, these
   can be LRAs, RAs, and CAs.

   A PKI management entity typically forwards request messages from
   downstream, but it may also reply to them itself.  Besides forwarding
   received messages, a PKI management entity may need to revoke
   certificates of EEs, report errors, or may need to manage its own
   certificates.

5.1.  Forwarding messages

   In case the PKI solution consists of several PKI management entities,
   each CMP request message (i.e., ir, cr, p10cr, kur, pollReq, or
   certConf) or error message coming from an EE or any other downstream
   PKI management entity MUST be sent to the next (upstream) PKI
   management entity.  Any received response message MUST be forwarded
   downstream to the next PKI management entity or EE.

   The PKI management entity SHOULD verify the protection, the syntax,
   the required message fields, the message type, and if applicable the
   authorization and the proof-of-possession of the message.  Additional
   checks or actions MAY be applied depending on the PKI solution
   requirements and concept.  If one of these verification procedures
   fails, the (L)RA SHOULD switch to the operation described in
   Section 5.3, i.e., respond with a negative response message and then
   MUST NOT forward the request message further upstream.

   A PKI management entity SHOULD not change the received message unless
   necessary.  The PKI management entity SHOULD only update the message
   protection if this is technically necessary.  Concrete PKI system
   specifications may define in more detail when to do so.

   This is particularly relevant in the upstream communication of a
   request message.

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   Each hop in a chain of PKI management entity has one or more
   functionalities, e.g., a PKI management entity may

   *  verify the identities of EEs or base authorization decisions for
      certification request processing on specific knowledge of the
      local setup, e.g., by consulting an inventory or asset management
      system,

   *  add fields to certificate request messages,

   *  store data from a message in a database for later usage or audit
      purposes,

   *  provide traversal of a network boundary,

   *  replace a MAC-based protection by a signature-based protection
      that can be verified also further upstream,

   *  double-check if the messages transferred back and forth are
      properly protected and well-formed,

   *  provide an authentic indication that it has performed all required
      checks,

   *  initiate a delayed enrollment due to offline upstream
      communication or registration officer interaction,

   *  grant the request of an EE to omit sending a confirmation message,
      or

   *  collect messages from ultiple LRAs and forward them jointly.

   Therefore, the decision if a message should be forwarded

   *  unchanged with the original protection,

   *  unchanged with a new protection, or

   *  changed with a new protection

   depends on the PKI solution design and the associated security policy
   (CP/CPS [RFC3647]).

   This section specifies the options a PKI management entity may
   implement and use.

   A PKI management entity MAY update the protection of a message if it

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   *  performs changes to the header or the body of the message,

   *  needs to securely indicate that it has done checks or validations
      on the message to one of the next (upstream) PKI components,

   *  needs to protect the message using a key and certificate from a
      different PKI, or

   *  needs to replace or produce a MAC-based protection.

   This is particularly relevant in the upstream communication of
   certificate request messages.

   Note that the message protection covers only the header and the body
   and not the extraCerts.  The PKI management entity MAY change the
   extraCerts in any of the following message adaptations, e.g., to
   sort, add, or delete certificates to support the next hop.  This may
   be particularly helpful to augment upstream messages with additional
   certificates or to reduce the number of certificates in downstream
   messages when forwarding to constrained devices.

5.1.1.  Not changing protection

   This variant means that a PKI management entity forwards a CMP
   message without changing the header, body, or protection.  In this
   case the PKI management entity acts more like a proxy, e.g., on a
   network boundary, implementing no specific RA-like security
   functionality that require an authentic indication to the PKI.  Still
   the PKI management entity might implement checks that result in
   refusing to forward the request message and instead responding with
   an error message as specified in Section 5.3.

   This variant of forwarding a message SHOULD be used for kur messages
   because their protection (using the certificate to be updated) MUST
   NOT be changed.  If the respective PKI management entity really needs
   approve such a request it MUST use a nested message as described in
   Section 5.1.3.

5.1.2.  Replacing protection

   The following two alternatives to forwarding a message can be used by
   any PKI management entity forwarding a CMP message with or without
   changes, while providing its own protection asserting approval of
   messages.  In this case the PKI management entity acts as an actual
   Registration Authority (RA), which implements important security
   functionality of the PKI.

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   Before replacing the existing protection by a new protection, the PKI
   management entity MUST verify the protection provided and approve its
   content including any own modifications.  For certificate requests
   the PKI management entity MUST verify (except in case of central key
   generation) the presence and contents of the proof-of-possession
   self-signature of the certTemplate using the public key of the
   requested certificate and MUST check that the EE, as authenticated by
   the message protection, is authorized to request a certificate with
   the subject as specified in the certTemplate.

   In case the received message has been protected by a CA or another
   PKI management entity, the current PKI management entity MUST verify
   its protection and approve its content including any own
   modifications.  For request messages the PKI management entity MUST
   check that the other PKI management entity, as authenticated by the
   protection of the incoming message, was authorized to issue or
   forward the request.

   These message adaptations MUST NOT be applied to kur request messages
   as described in Section 4.1.3 since their original protection using
   the key and certificate to be updated needs to be preserved, unless
   the regCtrl OldCertId is used to strongly identify the certificate to
   be updated.

   These message adaptations MUST NOT be applied to certificate request
   messages as described in Section 4.1.6since their original protection
   needs to be preserved up to the Key Generation Authority, which needs
   to use it for encrypting the new private key for the EE.

   In both the kur and central key generation cases, if a PKI management
   entity needs to state its approval of the original request message it
   MUST provide this using a nested message as specified in
   Section 5.1.3.

   When an intermediate PKI management entity modifies a message, it
   SHOULD NOT change the transactionID nor the sender and recipient
   nonce except as stated for delayed enrollment in Section 4.1.7.
   Section 4.1.7.

5.1.2.1.  Keeping proof-of-possession

   This variant of forwarding a message means that a PKI management
   entity forwards a CMP message with or without modifying the message
   header or body while preserving any included proof-of-possession.

   By replacing the existing protection using its own CMP protecting key
   the PKI management entity provides a proof of verifying and approving
   of the message as described above.

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   In case the PKI management entity modifies the certTemplate of an ir
   or cr message, the message adaptation in Section 5.1.2.2 needs to be
   applied instead.

5.1.2.2.  Breaking proof-of-possession

   This variant of forwarding a message means that a PKI management
   entity forwards an ir or cr message with modifications of the
   certTemplate, i.e., modification, addition, or removal of fields.
   Such changes will break the signature-based proof-of-possession
   provided by the EE in the original message.

   By replacing the existing protection and using its own CMP protection
   key the PKI management entity provides a proof of verifying and
   approving the request message as described above.

   In addition, the PKI management entity MUST verify the proof-of-
   possession contained in the original message as described above.  If
   these checks were successful, the PKI management entity MUST change
   the popo to raVerified.

   The popo field MUST contain the raVerified choice in the certReq
   structure of the modified message as follows:

       popo
         raVerified              REQUIRED
       -- MUST have the value NULL and indicates that the PKI
       -- management entity verified the popo of the original
       -- message

5.1.3.  Adding Protection

   This variant of forwarding a message means that a PKI management
   entity adds another protection to PKI management messages before
   forwarding them.  Applying an additional protection is specifically
   relevant when forwarding a message that requests a certificate update
   or a central key generation.  This is because the original protection
   of the EE must be preserved while adding an indication of approval.

   The nested message is a PKI management message containing a
   PKIMessages sequence as its body containing one or more CMP messages.

   As specified in the updated Section 5.1.3.4 of RFC4210 [RFC4210] (see
   CMP Updates [I-D.ietf-lamps-cmp-updates]) there are various use case
   for adding another protection by a PKI management entity.  Specific
   procedures are described in more detail in the following sections.

   The behavior in case an error occurs is described in Section 4.3.

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   Message flow:

   Step# PKI management entity               PKI management entity
    1   format nested
    2                      ->  nested   ->
    3                                        handle, re-protect or
                                               forward nested
    4                                        format or receive nested
    5                      <-  nested   <-
    6   handle nested

   Detailed message description:

   Nested Message - nested

   Field                         Value

   header
       -- As described in Section 3.1

   body
       -- Container to provide additional protection to original
       -- messages and to bundle request messages or alternatively
       -- response messages
     PKIMessages                 REQUIRED
       -- MUST be a sequence of one or more CMP messages

   protection                    REQUIRED
       -- As described in Section 3.2 using the CMP protection key of
       -- the PKI management entity

   extraCerts                    REQUIRED
       -- As described in Section 3.3

5.1.3.1.  Handling a single PKI management message

   A PKI management entity may authentically indicate successful
   validation and authorization of a PKI management message by adding an
   additional signature to the original PKI management message.

   A PKI management entity SHALL wrap the original PKI management
   messages in a nested message structure.  The additional signature as
   prove of verification and authorization by the PKI management entity
   MUST be applied as signature-based message protection of the nested
   message.

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5.1.3.2.  Handling a batch of PKI management messages

   A PKI management entity MAY bundle any number of PKI management
   messages for batch processing or to transfer a bulk of PKI management
   messages via an offline interface using the nested message structure.
   Nested messages can be used on the upstream interface towards the
   next PKI management entity and/or on the downstream interface from
   the PKI management entity towards the EE.

   This PKI management operation is typically used on the interface
   between LRA and RA to bundle several PKI management messages for
   offline transport.  In this case the LRA needs to initiate delayed
   enrollment as described in Section 5.1.4.  If the RA may need
   different routing information per nested PKI management message a
   suitable mechanism may need to be implemented.  This mechanism
   strongly depends on the requirements of the target architecture.
   Therefore, it is out of scope of this document.

   An initial nested message is generated locally at the PKI management
   entity.  For the initial nested message, the PKI management entity
   acts as a protocol end point and therefore a fresh transactionId and
   a fresh senderNonce MUST be used in the header of the nested message.
   The recipient field MUST identify the PKI management entity that is
   expected to unpack the nested message.  An initial nested message may
   contain request messages, e.g., ir, cr, p10cr, kur, certConf, rr, or
   genm.  While building the initial nested message the PKI management
   entity SHOULD store the transactionIds and the senderNonces of all
   bundled messages together with the transactionId of the initial
   nested message.

   Such an initial nested message is sent to the next PKI management
   entity, which MUST unbundle the included request messages and handle
   each of them as usual.  It SHOULD answer with a responding nested
   message.  This responding message MUST use the transactionId of the
   initial nested message and return the senderNonce of the initial
   nested message as recipNonce of the responding nested message.  The
   responding nested message SHOULD bundle the individual response
   messages (e.g., ip, cp, kup, pkiconf, rp, genp, error) for all
   original request messages of the initial nested message.  While
   unbundling the responding nested message, the former PKI management
   entity can determine lost and unexpected responses based on the
   previously stored transactionIds and senderNonces.  When it forwards
   the unbundled responses, any extra messages SHOULD be dropped, and
   any missing message SHOULD be replaced by an error message to inform
   the respective EE about the failed certificate management operation.

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   The PKI management entity building the nested message applies a
   signature-based protection using its CMP protection key as transport
   protection.  This protection SHALL NOT be regarded as an indication
   of verification or approval of the bundled PKI request messages.

5.1.4.  Initiating delayed enrollment

   This functional extension can be used by a PKI management entity to
   initiate delayed enrollment.  In this case a PKI management entity
   MUST set the status "waiting" in the response message.  The PKI
   management entity MUST then reply to the pollReq messages as
   described in Section 4.1.7.

   Typically, as stated in Section 5.1.2, an intermediate PKI management
   entity SHOULD NOT change the sender and recipient nonces even in case
   it modifies a request or a response message.  In the special case of
   polling initiated by an intermediate PKI management entity, for
   example by an LRA with offline transport to an upstream RA, there is
   an exception.  Between the EE and that entity, pollReq and pollRep
   messages are exchanged handling the nonces as usual.  Yet when, after
   some pollRep, the final response from upstream arrives at that PKI
   management entity, this response contains the recipNonce set to the
   value copied (as usual) from the senderNonce in the original request
   message.  The mentioned entity needs to replace the recipNonce in the
   response message with the senderNonce of the last received pollReq
   because the downstream entities, including the EE, will expect it in
   this way.

5.2.  Revoking certificates on behalf of another's PKI entities

   This PKI management operation can be used by a PKI management entity
   to revoke a certificate of another PKI entity.  This revocation
   request message MUST be signed by the PKI management entity using its
   own CMP protection key to prove to the PKI authorization to revoke
   the certificate on behalf of that PKI entity.

   Preconditions:

   1  the certificate to be revoked MUST be known to the PKI management
      entity

   2  the PKI management entity MUST have the authorization to revoke
      the certificates of other entities issued by the corresponding CA

   The message sequence for this PKI management operation is identical
   to that given in Section 4.2, with the following changes:

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   1  it is not required that the certificate to be revoked is not yet
      expired or revoked

   2  the PKI management entity acts as EE for this message exchange

   3  the rr message MUST be signed using the CMP protection key of the
      PKI management entity.

5.3.  Error reporting

   This functionality should be used by the PKI management entity to
   report any arising error conditions downstream to the EE.  Note that
   error reporting by the EE upstream to the PKI management entity is
   described in Section 4.3.

   In case the error condition is related to specific details of an ir,
   cr, p10cr, or kur request message it MUST be reported in the specific
   response message, i.e., an ip, cp, or kup with negative contents.

   General error conditions, e.g., problems with the message header,
   protection, or extraCerts, and negative feedback on rr, pollReq,
   certConf, or error messages MUST be reported in the form of an error
   message.

   In both situations the PKI management entity reports the errors in
   the PKIStatusInfo structure of the respective message as described in
   Section 4.3.

   An EE receiving any such negative feedback SHOULD log the error
   appropriately and MUST terminate the current transaction.

6.  CMP message transport mechanisms

   The CMP messages are designed to be self-contained, such that in
   principle any transport can be used.  HTTP SHOULD be used for online
   transport while file-based transport MAY be used in case offline
   transport is required.  In case HTTP transport is not desired or
   possible, CMP messages MAY also be piggybacked on any other reliable
   transport protocol such as CoAP [RFC7252].

   Independently of the means of transport it can happen that messages
   are lost or that a communication partner does not respond.  To
   prevent waiting indefinitely, each CMP client component SHOULD use a
   configurable per-request timeout, and each CMP server component
   SHOULD use a configurable per-response timeout in case a further
   message is to be expected from the client side.  In this way a
   hanging transaction can be closed cleanly with an error and related
   resources (for instance, any cached extraCerts) can be freed.

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   When conveying a CMP messages in HTTP or MIME-based transport
   protocols the internet media type "application/pkixcmp" MUST be set
   for transport encoding as specified in Section 5.3 of RFC 2510
   [RFC2510] and Section 3.4 of RFC 6712 [RFC6712].

   Note: When using TCP as reliable transport layer protocol, which is
   typical in conjunction with HTTP, there is the option to keep the
   connection open over the lifetime of transactions containing multiple
   request-response message pairs.  This may improve efficiency but is
   not required from a security point of view.

6.1.  HTTP transport

   This transport mechanism can be used by a PKI entity to transfer CMP
   messages over HTTP.  If HTTP transport is used the specifications as
   described in [RFC6712] and updated by CMP Updates
   [I-D.ietf-lamps-cmp-updates] MUST be followed.

   PKI management operations SHOULD use the following URI path:

   +=================================+=====================+=========+
   | PKI management operation        |         Path        | Details |
   +=================================+=====================+=========+
   | Enroll client to new PKI        |   /initialization   | Section |
   |                                 |                     | 4.1.1   |
   +---------------------------------+---------------------+---------+
   | Enroll client to existing PKI   |    /certification   | Section |
   |                                 |                     | 4.1.2   |
   +---------------------------------+---------------------+---------+
   | Update client certificate       |      /keyupdate     | Section |
   |                                 |                     | 4.1.3   |
   +---------------------------------+---------------------+---------+
   | Enroll client using PKCS#10     |         /p10        | Section |
   |                                 |                     | 4.1.5   |
   +---------------------------------+---------------------+---------+
   | Enroll client using central key |    /serverkeygen    | Section |
   | generation                      |                     | 4.1.6   |
   |                                 |                     |         |
   | Note: This path element MAY     |                     |         |
   | also be appended to each of the |                     |         |
   | path elements listed above.     |                     |         |
   +---------------------------------+---------------------+---------+
   | Revoke client certificate       |     /revocation     | Section |
   |                                 |                     | 4.2     |
   +---------------------------------+---------------------+---------+
   | Get CA certificates             |      /getcacert     | Section |
   |                                 |                     | 4.4.1   |
   +---------------------------------+---------------------+---------+

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   | Get root CA certificate update  |    /getrootupdate   | Section |
   |                                 |                     | 4.4.2   |
   +---------------------------------+---------------------+---------+
   | Get certificate request         | /getcertreqtemplate | Section |
   | template                        |                     | 4.4.3   |
   +---------------------------------+---------------------+---------+
   | Additional protection           |       /nested       | Section |
   |                                 |                     | 5.1.3   |
   | Note: This path element is      |                     |         |
   | applicable only between PKI     |                     |         |
   | management entities.            |                     |         |
   +---------------------------------+---------------------+---------+

                         Table 9: HTTP endpoints

   Subsequent certConf, error, and pollReq messages are sent to the URI
   of the respective PKI management operation.

   The PKI entity will recognize by the HTTP response status code if a
   configured URI is supported by the PKI management entity by sending a
   request to its preferred enrollment endpoint.

6.2.  HTTPS transport using certificates

   This transport mechanism can be used by a PKI entity to further
   protect the HTTP transport described in Section 6.1 using TLS 1.2
   [RFC5246] or TLS 1.3 [RFC8446] with certificate-based authentication
   as described in [RFC2818].  Using this transport mechanism, the CMP
   transport via HTTPS MUST use TLS server authentication and SHOULD use
   TLS client authentication.

   TLS client:

   *  The client SHOULD use a TLS client certificate as far as
      available.  If no dedicated TLS certificate is available on an EE
      side, this EE SHOULD use an already existing certificate
      identifying the EE (e.g., a manufacturer issued certificate).
      Each PKI management entity SHOULD use a dedicated TLS client
      certificate on its upstream (client) interface.

   *  If no usable client certificate is available at the client,
      server-only authenticated TLS MUST be used.

   *  The client MUST validate the TLS server certificate of its
      communication partner.

   TLS server:

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   *  The server MUST use a TLS server certificate.

   *  The server MUST validate the TLS certificate of its clients if
      client authentication is available.

   Note: The requirements for checking certificates given in [RFC5280],
   [RFC5246] and [RFC8446] MUST be followed for the TLS layer.
   Certificate status checking SHOULD be used for the TLS certificates
   of communication partners.

6.3.  HTTPS transport using shared secrets

   This transport mechanism can be used by a PKI entity to further
   protect the HTTP transport as described in Section 6.1 using TLS 1.2
   [RFC5246] or TLS 1.3 [RFC8446] as described in [RFC2818] with mutual
   authentication based on shared secret information as described in
   [RFC5054].

   < TBD: Add an appropriate shared secret-based mechanism for TLS 1.3.
   >

   TLS client:

   *  The client MUST use its shared secret information for
      authentication.

   TLS server:

   *  The server MUST use a suitable shared secret information for
      authentication.

   < TBD: It needs to be clarified which cipher suite shall be
   recommended as there seems to be no support for TLS-SRP un JavaSE. >

6.4.  Offline transport

   For transporting CMP messages between PKI entities any mechanism can
   be used that is able to store and forward binary objects of
   sufficient length and with sufficient reliability while preserving
   the order of messages for each transaction.

   The transport mechanism SHOULD be able to indicate message loss,
   excessive delay, and possibly other transmission errors.  In such
   cases the PKI entities using this mechanism SHOULD report an error as
   specified in Section 4.3 as fare as possible.

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6.4.1.  File-based transport

   CMP messages MAY be transferred between PKI entities using file-
   system-based mechanisms, for instance when an off-line end entity or
   a PKI management entity performs delayed enrollment.  Each file MUST
   contain the ASN.1 DER encoding of one CMP message only, which may be
   nested.  There MUST be no extraneous header or trailer information in
   the file.  The file name extension ".PKI" MUST be used.

6.4.2.  Other asynchronous transport protocols

   Other asynchronous transport protocols, e.g., email or website
   up-/download, MAY transfer CMP messages between PKI entities.  A MIME
   wrapping is defined for those environments that are MIME native.  The
   MIME wrapping in this section is specified in [RFC8551], section 3.1.

   The ASN.1 DER encoding of the CMP messages MUST be transferred using
   the "application/pkixcmp" content type and base64-encoded content-
   transfer-encoding as specified in [RFC2510], section 5.3.  A filename
   MUST be included either in a content-type or a content-disposition
   statement.  The file name extension ".PKI" MUST be used.

6.5.  CoAP transport

   In constrained environments where no HTTP transport is desired or
   possible, CoAP [RFC7252] as specified in
   [I-D.ietf-ace-cmpv2-coap-transport] MAY be used.

6.6.  Piggybacking on other reliable transport

   For online transfer where no HTTP transport is desired or possible
   CMP messages MAY also be transported on some other reliable protocol.
   Connection and error handling mechanisms like those specified for
   HTTP in [RFC6712] need to be implemented.

   A more detailed specification is out of scope of this document and
   would need to be given in a separate document, for instance in the
   scope of the transport protocol used.

7.  IANA Considerations

8.  Security Considerations

   < TBD: Add any security considerations >

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9.  Acknowledgements

   We thank the various reviewers of this document.

10.  References

10.1.  Normative References

   [I-D.ietf-lamps-cmp-algorithms]
              Brockhaus, H., Aschauer, H., Ounsworth, M., and S. Mister,
              "CMP Algorithms", Work in Progress, Internet-Draft, draft-
              ietf-lamps-cmp-algorithms-02, 20 January 2021,
              <https://tools.ietf.org/html/draft-ietf-lamps-cmp-
              algorithms-02>.

   [I-D.ietf-lamps-cmp-updates]
              Brockhaus, H. and D. V. Oheimb, "Certificate Management
              Protocol (CMP) Updates", Work in Progress, Internet-Draft,
              draft-ietf-lamps-cmp-updates-08, 22 February 2021,
              <https://tools.ietf.org/html/draft-ietf-lamps-cmp-updates-
              08>.

   [I-D.ietf-lamps-crmf-update-algs]
              Housley, R., "Algorithm Requirements Update to the
              Internet X.509 Public Key Infrastructure Certificate
              Request Message Format (CRMF)", Work in Progress,
              Internet-Draft, draft-ietf-lamps-crmf-update-algs-04, 19
              February 2021, <https://tools.ietf.org/html/draft-ietf-
              lamps-crmf-update-algs-04>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/info/rfc2986>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

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   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              DOI 10.17487/RFC4211, September 2005,
              <https://www.rfc-editor.org/info/rfc4211>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/info/rfc5652>.

   [RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958,
              DOI 10.17487/RFC5958, August 2010,
              <https://www.rfc-editor.org/info/rfc5958>.

   [RFC6712]  Kause, T. and M. Peylo, "Internet X.509 Public Key
              Infrastructure -- HTTP Transfer for the Certificate
              Management Protocol (CMP)", RFC 6712,
              DOI 10.17487/RFC6712, September 2012,
              <https://www.rfc-editor.org/info/rfc6712>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [ETSI-3GPP.33.310]
              3GPP, "Network Domain Security (NDS); Authentication
              Framework (AF)", 3GPP TS 33.310 16.6.0, 16 December 2020.

   [I-D.ietf-ace-cmpv2-coap-transport]
              Sahni, M. and S. Tripathi, "CoAP Transport for CMPV2",
              Work in Progress, Internet-Draft, draft-ietf-ace-cmpv2-
              coap-transport-00, 21 February 2021,
              <https://tools.ietf.org/html/draft-ietf-ace-cmpv2-coap-
              transport-00>.

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   [IEC.62443-3-3]
              IEC, "Industrial communication networks - Network and
              system security - Part 3-3: System security requirements
              and security levels", IEC 62443-3-3, August 2013,
              <https://webstore.iec.ch/publication/7033>.

   [IEEE.802.1AR_2018]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks - Secure Device Identity", IEEE 802.1AR-2018,
              DOI 10.1109/IEEESTD.2018.8423794, 2 August 2018,
              <https://ieeexplore.ieee.org/document/8423794>.

   [NIST.CSWP.04162018]
              National Institute of Standards and Technology (NIST),
              "Framework for Improving Critical Infrastructure
              Cybersecurity, Version 1.1", NIST NIST CSWP 04162018,
              DOI 10.6028/NIST.CSWP.04162018, April 2018,
              <http://nvlpubs.nist.gov/nistpubs/CSWP/
              NIST.CSWP.04162018.pdf>.

   [NIST.SP.800-57p1r5]
              Barker, E B., "Recommendation for key management, part 1
              :general", NIST NIST.SP.800-57pt1r5,
              DOI 10.6028/NIST.SP.800-57pt1r5, 2020,
              <https://doi.org/10.6028/NIST.SP.800-57pt1r5>.

   [RFC2510]  Adams, C. and S. Farrell, "Internet X.509 Public Key
              Infrastructure Certificate Management Protocols",
              RFC 2510, DOI 10.17487/RFC2510, March 1999,
              <https://www.rfc-editor.org/info/rfc2510>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC3647]  Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S.
              Wu, "Internet X.509 Public Key Infrastructure Certificate
              Policy and Certification Practices Framework", RFC 3647,
              DOI 10.17487/RFC3647, November 2003,
              <https://www.rfc-editor.org/info/rfc3647>.

   [RFC5054]  Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
              "Using the Secure Remote Password (SRP) Protocol for TLS
              Authentication", RFC 5054, DOI 10.17487/RFC5054, November
              2007, <https://www.rfc-editor.org/info/rfc5054>.

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   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,
              <https://www.rfc-editor.org/info/rfc8366>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8551]  Schaad, J., Ramsdell, B., and S. Turner, "Secure/
              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
              Message Specification", RFC 8551, DOI 10.17487/RFC8551,
              April 2019, <https://www.rfc-editor.org/info/rfc8551>.

   [UNISIG.Subset-137]
              UNISIG, "Subset-137; ERTMS/ETCS On-line Key Management
              FFFIS; V1.0.0", December 2015,
              <https://www.era.europa.eu/filebrowser/download/542_en>.

Appendix A.  Example CertReqTemplate

   This section provides a concrete example for the content of an
   infoValue used of type id-it-certReqTemplate as described in
   Section 4.4.3.

   Suppose the server requires that the certTemplate contains the issuer
   field with a value to be filled in by the EE, the subject field with
   a common name to be filled in by the EE and two organizational unit
   fields with given values "myDept" and "myGroup", the publicKey field
   with an ECC key on curve secp256r1 or RSA public key of length 2048,
   the subjectAltName extension with DNS name "www.myServer.com" and an
   IP address to be filled in, the keyUsage extension marked critical
   with the value digitalSignature and keyAgreement, and the extKeyUsage
   extension with values to be filled in by the EE.  Then the infoValue
   with certTemplate and keySpec returned to the EE must be encoded as
   follows:

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   SEQUENCE {
     SEQUENCE {
       [3] {
         SEQUENCE {}
         }
       [5] {
         SEQUENCE {
           SET {
             SEQUENCE {
               OBJECT IDENTIFIER commonName (2 5 4 3)
               UTnF8String ''
               }
             }
             SEQUENCE {
               OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
               UTF8String 'myDept'
               }
             }
           SET {
             SEQUENCE {
               OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
               UTF8String 'myGroup'
               }
             }
           }
       [6] {
         SEQUENCE {
           null
           NULL
           }
         BIT STRING, encapsulates {
           SEQUENCE {}
           }
         }
       [9] {
         SEQUENCE {
           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
           OCTET STRING, encapsulates {
             SEQUENCE {
               [2] 'www.myServer.com'
               [7] ''
               }
             }
           }
         SEQUENCE {
           OBJECT IDENTIFIER keyUsage (2 5 29 15)
           BOOLEAN TRUE
           OCTET STRING, encapsulates {

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             BIT STRING 3 unused bits
               '10001'B
             }
           }
         SEQUENCE {
           OBJECT IDENTIFIER extKeyUsage (2 5 29 37)
           OCTET STRING, encapsulates {
             SEQUENCE {}
             }
           }
         }
       }
     SEQUENCE {
       SEQUENCE {
         OBJECT IDENTIFIER aldId (1 3 6 1 5 5 7 5 1 TBD3)
           SEQUENCE {
             OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
             OBJECT IDENTIFIER secp256r1 (1 2 840 10045 3 1 7)
             }
         }
       SEQUENCE {
         OBJECT IDENTIFIER rsaKeyLen (1 3 6 1 5 5 7 5 1 TBD4)
         INTEGER 2048
         }
       }
     }

Appendix B.  History of changes

   Note: This appendix will be deleted in the final version of the
   document.

   From version 04 -> 05:

   *  Changed to XML V3
   *  Added algorithm names introducted in CMP Algorithms Section 7.3 to
      Section 4 of this document
   *  Updates Syntax in Section 4.4.3 due to changes made in CMP Updates
   *  Deleted the text on HTTP-based discovery as discussed in
      Section 6.1
   *  Updates Appendix A due to change syntax in Section 4.4.3
   *  Many clarifications and changes in wording thanks to David's
      extensive review

   From version 03 -> 04:

   *  Deleted normative text sections on algorithms and refer to CMP
      Algorithms and CRMF Algorithm Requirements Update instead

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   *  Some clarifications and changes in wording

   From version 02 -> 03:

   *  Updated the interoperability with [UNISIG.Subset-137] in
      Section 1.4.
   *  Changed Section 2.3 to a tabular layout to enhanced readability
   *  Added a ToDo to section 3.1 on aligning with the CMP Algorithms
      draft that will be set up as decided in IETF 108
   *  Updated section 4.1.6 to add the AsymmetricKey Package structure
      to transport a newly generated private key as decided in IETF 108
   *  Added a ToDo to section 4.1.7 on required review of the nonce
      handling in case an offline LRA responds and not forwards the
      pollReq messages
   *  Updated Section 4 due to the definition of the new ITAV OIDs in
      CMP Updates
   *  Updated Section 4.4.4 to utilize controls instead of rsaKeyLen
      (see thread "dtaft-ietf-lamps-cmp-updates and rsaKeyLen")
   *  Deleted the section on definition and discovery of HTTP URIs and
      copied the text to the HTTP transport section and to CMP Updates
      section 3.2
   *  Added some explanation to Section 5.1.2 and Section 5.1.3 on using
      nested messages when a protection by the RA is required.
   *  Deleted the section on HTTP URI definition and discovery as some
      content was moved to CMP Updates.  The rest of the content was
      moved back to the HTTP transport section
   *  Deleted the ASN.1 module after moving the new OIDs id-it-caCerts,
      id-it-rootCaKeyUpdate, and id-it-certReqTemplate to CMP Updates
   *  Minor changes in wording and addition of some open ToDos

   From version 01 -> 02:

   *  Extend Section 1.4 with regard to conflicts with UNISIG Subset-
      137.
   *  Minor clarifications on extraCerts in Section 3.3 and
      Section 4.1.1.
   *  Complete specification of requesting a certificate from a trusted
      PKI with signature protection in Section 4.1.2.
   *  Changed from symmetric key-encryption to password-based key
      management technique in section Section 4.1.6.3 as discussed on
      the mailing list (see thread "draft-ietf-lamps-lightweight-cmp-
      profile-01, section 5.1.6.1")
   *  Changed delayed enrollment described in Section 4.1.7 from
      recommended to optional as decided at IETF 107
   *  Introduced the new RootCAKeyUpdate structure for root CA
      certificate update in Section 4.4.2 as decided at IETF 107 (also
      see email thread "draft-ietf-lamps-lightweight-cmp-profile-01,
      section 5.4.3")

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   *  Extend the description of the CertReqTemplate PKI management
      operation, including an example added in the Appendix.  Keep
      rsaKeyLen as a single integer value in Section 4.4.3 as discussed
      on the mailing list (see thread "draft-ietf-lamps-lightweight-cmp-
      profile-01, section 5.4.4")
   *  Deleted Sections "Get certificate management configuration" and
      "Get enrollment voucher" as decided at IETF 107
   *  Complete specification of adding an additional protection by an
      PKI management entity in Section 5.1.3.
   *  Added a section on HTTP URI definition and discovery and extended
      Section 6.1 on definition and discovery of supported HTTP URIs and
      content types, add a path for nested messages as specified in
      Section 5.1.3 and delete the paths for /getCertMgtConfig and
      /getVoucher
   *  Changed Section 6.4 to address offline transport and added more
      detailed specification file-based transport of CMP
   *  Added a reference to the new I-D of Mohit Sahni on "CoAP Transport
      for CMPV2" in Section 6.5; thanks to Mohit supporting the effort
      to ease utilization of CMP
   *  Moved the change history to the Appendix
   *  Minor changes in wording

   From version 00 -> 01:

   *  Harmonize terminology with CMP [RFC4210], e.g.,
      -  transaction, message sequence, exchange, use case -> PKI
         management operation
      -  PKI component, (L)RA/CA -> PKI management entity
   *  Minor changes in wording

   From draft-brockhaus-lamps-lightweight-cmp-profile-03 -> draft-ietf-
   lamps-lightweight-cmp-profile-00:

   *  Changes required to reflect WG adoption
   *  Minor changes in wording

   From version 02 -> 03:

   *  Added a short summary of [RFC4210] Appendix D and E in
      Section 1.3.
   *  Clarified some references to different sections and added some
      clarification in response to feedback from Michael Richardson and
      Tomas Gustavsson.
   *  Added an additional label to the operational path to address
      multiple CAs or certificate profiles in Section 6.1.

   From version 01 -> 02:

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   *  Added some clarification on the key management techniques for
      protection of centrally generated keys in Section 4.1.6.
   *  Added some clarifications on the certificates for root CA
      certificate update in Section 4.4.2.
   *  Added a section to specify the usage of nested messages for RAs to
      add an additional protection for further discussion, see
      Section 5.1.3.
   *  Added a table containing endpoints for HTTP transport in
      Section 6.1 to simplify addressing PKI management entities.
   *  Added some ToDos resulting from discussion with Tomas Gustavsson.
   *  Minor clarifications and changes in wording.

   From version 00 -> 01:

   *  Added a section to specify the enrollment with an already trusted
      PKI for further discussion, see Section 4.1.2.
   *  Complete specification of requesting a certificate from a legacy
      PKI using a PKCS#10 [RFC2986] request in Section 4.1.5.
   *  Complete specification of adding central generation of a key pair
      on behalf of an end entity in Section 4.1.6.
   *  Complete specification of handling delayed enrollment due to
      asynchronous message delivery in Section 4.1.7.
   *  Complete specification of additional support messages, e.g., to
      update a Root CA certificate or to request an RFC 8366 [RFC8366]
      voucher, in Section 4.4.
   *  Minor changes in wording.

   From draft-brockhaus-lamps-industrial-cmp-profile-00 -> draft-
   brockhaus-lamps-lightweight-cmp-profile-00:

   *  Change focus from industrial to more multi-purpose use cases and
      lightweight CMP profile.
   *  Incorporate the omitted confirmation into the header specified in
      Section 3.1 and described in the standard enrollment use case in
      Section 4.1.1 due to discussion with Tomas Gustavsson.
   *  Change from OPTIONAL to RECOMMENDED for use case 'Revoke another's
      entities certificate' in Section 5.2, because it is regarded as
      important functionality in many environments to enable the
      management station to revoke EE certificates.
   *  Complete the specification of the revocation message flow in
      Section 4.2 and Section 5.2.
   *  The CoAP based transport mechanism and piggybacking of CMP
      messages on top of other reliable transport protocols is out of
      scope of this document and would need to be specified in another
      document.
   *  Further minor changes in wording.

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Authors' Addresses

   Hendrik Brockhaus (editor)
   Siemens AG

   Email: hendrik.brockhaus@siemens.com

   Steffen Fries
   Siemens AG

   Email: steffen.fries@siemens.com

   David von Oheimb
   Siemens AG

   Email: david.von.oheimb@siemens.com

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