Enrollment over Secure Transport
draft-ietf-pkix-est-06
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7030.
|
|
|---|---|---|---|
| Authors | Max Pritikin , Peter E. Yee , Dan Harkins | ||
| Last updated | 2013-05-26 (Latest revision 2013-03-29) | ||
| Replaces | draft-pritikin-est | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 7030 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Sean Turner | ||
| Send notices to | pkix-chairs@tools.ietf.org, draft-ietf-pkix-est@tools.ietf.org |
draft-ietf-pkix-est-06
PKIX M. Pritikin, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track P. Yee, Ed.
Expires: September 30, 2013 AKAYLA, Inc.
D. Harkins, Ed.
Aruba Networks
March 29, 2013
Enrollment over Secure Transport
draft-ietf-pkix-est-06
Abstract
This document profiles certificate enrollment for clients using
Certificate Management over CMS (CMC) messages over a secure
transport. This profile, called Enrollment over Secure Transport
(EST), describes a simple yet functional certificate management
protocol targeting Public Key Infrastructure (PKI) clients that need
to acquire client certificates and associated Certification Authority
(CA) certificate(s). It also supports client-generated public/
private key pairs as well as key pairs generated by the CA.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://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 September 30, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Operational Scenario Overviews . . . . . . . . . . . . . . . . 6
2.1. Obtaining CA Certificates . . . . . . . . . . . . . . . . 7
2.2. Initial Enrollment . . . . . . . . . . . . . . . . . . . . 8
2.2.1. Certificate TLS authentication . . . . . . . . . . . . 8
2.2.2. Certificate-less TLS authentication . . . . . . . . . 8
2.2.3. HTTP-based client authentication . . . . . . . . . . . 9
2.3. Client Certificate Re-issuance . . . . . . . . . . . . . . 9
2.4. Server Key Generation . . . . . . . . . . . . . . . . . . 9
2.5. Full PKI Request messages . . . . . . . . . . . . . . . . 9
2.6. Certificate Signing Request (CSR) Attributes Request . . . 9
3. Protocol Design and Layering . . . . . . . . . . . . . . . . . 10
3.1. Application Layer . . . . . . . . . . . . . . . . . . . . 14
3.2. HTTP Layer . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.1. HTTP headers for control . . . . . . . . . . . . . . . 15
3.2.2. HTTP URIs for control . . . . . . . . . . . . . . . . 16
3.2.3. HTTP-Based Client Authentication . . . . . . . . . . . 17
3.2.4. Message types . . . . . . . . . . . . . . . . . . . . 18
3.3. TLS Layer . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3.1. TLS-Based Server Authentication . . . . . . . . . . . 20
3.3.2. TLS-Based Client Authentication . . . . . . . . . . . 20
3.3.3. Certificate-less TLS Mutual Authentication . . . . . . 21
3.4. Proof-of-Possession . . . . . . . . . . . . . . . . . . . 21
3.5. Linking Identity and PoP information . . . . . . . . . . . 22
3.6. Server Authorization . . . . . . . . . . . . . . . . . . . 23
3.6.1. Client use of Explicit TA Database . . . . . . . . . . 23
3.6.2. Client use of Implicit TA Database . . . . . . . . . . 23
3.7. Client Authorization . . . . . . . . . . . . . . . . . . . 24
4. Protocol Exchange Details . . . . . . . . . . . . . . . . . . 24
4.1. Distribution of CA certificates . . . . . . . . . . . . . 24
4.1.1. Bootstrap Distribution of CA certificates . . . . . . 24
4.1.2. CA certificates request . . . . . . . . . . . . . . . 25
4.1.3. CA certificates response . . . . . . . . . . . . . . . 25
4.2. Client Certificate Request Functions . . . . . . . . . . . 27
4.2.1. Simple Enrollment of Clients . . . . . . . . . . . . . 27
4.2.2. Simple Re-Enrollment of Clients . . . . . . . . . . . 28
4.2.3. Simple Enroll and Re-Enroll Response . . . . . . . . . 28
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4.3. Full CMC . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.3.1. Full CMC Request . . . . . . . . . . . . . . . . . . . 29
4.3.2. Full CMC Response . . . . . . . . . . . . . . . . . . 29
4.4. Server-side Key Generation . . . . . . . . . . . . . . . . 30
4.4.1. Server-side Key Generation Request . . . . . . . . . . 30
4.4.1.1. Requests for Symmetric Key Encryption of the
Private Key . . . . . . . . . . . . . . . . . . . 31
4.4.1.2. Requests for Asymmetric Encryption of the
Private Key . . . . . . . . . . . . . . . . . . . 31
4.4.2. Server-side Key Generation Response . . . . . . . . . 31
4.5. CSR Attributes . . . . . . . . . . . . . . . . . . . . . . 33
4.5.1. CSR Attributes Request . . . . . . . . . . . . . . . . 33
4.5.2. CSR Attributes Response . . . . . . . . . . . . . . . 33
5. Contributors/Acknowledgements . . . . . . . . . . . . . . . . 35
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
7. Security Considerations . . . . . . . . . . . . . . . . . . . 36
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
8.1. Normative References . . . . . . . . . . . . . . . . . . . 38
8.2. Informative References . . . . . . . . . . . . . . . . . . 41
Appendix A. Operational Scenario Example Messages . . . . . . . . 42
A.1. Obtaining CA Certificates . . . . . . . . . . . . . . . . 42
A.2. Enroll/ReEnroll . . . . . . . . . . . . . . . . . . . . . 44
A.3. Server Key Generation . . . . . . . . . . . . . . . . . . 46
A.4. CSR Attributes . . . . . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 49
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1. Introduction
This document profiles certificate enrollment for clients using
Certificate Management over CMS (CMC) [RFC5272] messages over a
secure transport. Enrollment over Secure Transport (EST) describes
the use of Transport Layer Security (TLS) 1.1 [RFC4346] (or a later
version) and Hypertext Transfer Protocol (HTTP) 1.1 [RFC2616] (or a
later version) to provide an authenticated and authorized channel for
Simple PKI (Public Key Infrastructure) Requests and Responses
[RFC5272].
Architecturally, the EST service is located between a CA and a client
device. It performs several functions traditionally allocated to the
RA (Registration Authority) role in a PKI. The nature of
communication between an EST server and a CA is not described in this
document.
EST adopts the Certificate Management Protocol (CMP) [RFC4210] model
for CA certificate rollover, but does not use the CMP message syntax
or protocol. EST servers are extensible in that new functions may be
defined to provide additional capabilities not specified in CMC
[RFC5272], and this document defines two such extensions, one for
requesting Certificate Signing Request attributes, and another for
requesting server-generated keys.
EST specifies how to transfer messages securely via HTTP over TLS
(HTTPS) [RFC2818], where the HTTP headers and content types are used
in conjunction with TLS. HTTPS operates over TCP; this document does
not specify EST over Datagram Transport Layer Security/User Datagram
Protocol (DTLS/UDP). Figure 1 shows how the layers build upon each
other.
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EST Layering:
Protocols:
+--------------------------------------------+
| |
| EST request/response messages |
| |
+--------------------------------------------+
| |
| HTTP for message transfer and signaling |
| |
+--------------------------------------------+
| |
| TLS for transport security |
| |
+--------------------------------------------+
| |
| TCP for transport |
| |
+--------------------------------------------+
Figure 1
[[EDNOTE: Comments such as this one, included within double brackets
and initiated with an 'EDNOTE', are for editorial use and shall be
removed as the document is polished.]]
1.1. 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 [RFC2119].
It is assumed that the reader is familiar with the terms and concepts
described in Public Key Cryptography Standard (PKCS) #10 [RFC2314],
HTTPS [RFC2818], CMP [RFC4210], CMC [RFC5272][RFC5273][RFC5274], and
TLS [RFC4346].
In addition to the terms defined in the terminology section of CMC
[RFC5272] the following terms are defined for clarity:
EST CA: For certificate issuing services, the EST CA is reached
through the EST Server; the CA could be logically "behind" the EST
Server or embedded within it.
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Third-Party Trust Anchor (TA): Any Trust Anchor that is not
authoritative for the PKI hierarchy the EST server is providing
services for.
Explicit Trust Anchor: Any Trust Anchor that is explicitly
configured on the client or server for use during EST TLS
authentication. For example a TA that is manually configured on
the EST client or bootstrapped as described in Section 4.1.1.
(See more details in Section 3.6 and Section 7).
Implicit Trust Anchor: Any third-party Trust Anchor that is
available on the client or server for use during TLS
authentication but is not specifically indicated for use during
EST TLS authentication. For example TAs commonly used by web
browsers to authenticate web servers, or TAs used by server's to
authenticate manufacturing installed client credentials. The
authorization model for these TAs is different from the
authorization model for Explicit Trust Anchors. (See more details
in Section 3.6.1, Section 3.6.2, and Section 7).
Certificate-less TLS: Use of a TLS cipher suite in which neither the
client nor server use a certificate to authenticate. The
credential used for authentication is a word, phrase, code or key
that is shared between the client and server. The credential must
be uniquely shared between the client and server in order to
provide authentication of an individual client.
2. Operational Scenario Overviews
This section provides an informative overview of the operational
scenarios to better introduce the reader to the protocol discussion.
This section does not include RFC 2119 key words.
Both the EST clients and server are configured with information that
provides the basis for bidirectional authentication and for
authorization. The specific initialization data depends on the
methods available in the client device and server, but can include
shared secrets, network service names and locations (e.g., a Uniform
Resource Identifier (URI) [RFC3986]), trust anchor information (e.g.,
a CA certificate or a hash of a TA's certificate), and enrollment
keys and certificates. Depending on an enterprise's acquisition and
network management practices, some initialization may be performed by
the vendor prior to delivery of client hardware and software. In
that case, the client device vendor may provide data, such as trust
anchors, to the enterprise via a secure procedure. The distribution
of this initial information is out of scope.
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Distribution of trust anchors and other certificates can be effected
via the EST server. However, nothing can be inferred about the
authenticity of this data until an out-of-band mechanism is used to
verify them.
Sections 2.1-2.3 very closely mirror the text of the Scenarios
Appendix of [RFC6403] with such modifications as are appropriate for
this profile. Sections 2.1-2.6, below, enumerate the set of EST
functions (see Figure 5) and provide an informative overview of EST's
capabilities.
The general client/server interaction proceeds as follows: The client
device initiates a TLS-secured HTTP session with an EST server. A
specific EST service is requested based on a portion of the URI used
for the session. The client device and server authenticate each
other. The client verifies that the server is authorized to serve
this client. The server verifies that the client is authorized to
make use of this server and the request that the client has made.
The server acts upon the client request.
2.1. Obtaining CA Certificates
The EST client can request a copy of the current EST CA certificates
from the EST server. The EST client is assumed to perform this
operation before performing other operations.
Throughout this document we assume the EST CA has a certificate that
is used by the client to verify signed objects issued by the CA,
e.g., certificates and certificate revocation lists (CRLs), and that
a separate end-entity (EE) certificate is used when EST protocol
communication requires additional encryption. This operation is used
to obtain the EST CA certificate(s).
The EST client authenticates and verifies the authorization scope of
the EST server when requesting the current CA certificate(s). As
detailed in Section 3.3.1 and Section 3.3.3, available options
include:
o Verifying the EST server's HTTPS URI against the EST server's
certificate using Implicit TAs (similar to a common HTTPS
exchange). This allows the EST server and client to leverage
existing TAs that might be known to the EST client.
o The client can leverage a previously distributed trust anchor
specific to the EST server. This allows the EST client to use an
existing, potentially older, CA certificate to request a current
CA certificate.
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o For bootstrapping, the EST client can rely upon manual
authentication performed by the end user as detailed in
Section 4.1.1.
Client authentication is not required for this exchange, so it is
trivially supported by the EST server.
2.2. Initial Enrollment
After authenticating an EST server and verifying that it is
authorized to provide services to the client, an EST client can
acquire a certificate for itself by submitting an enrollment request
to that server.
The EST server authenticates and authorizes the EST client as
specified in Section 3.3.2, Section 3.3.3 and Section 3.7. The
methods described in the normative text that are discussed in this
overview include:
o TLS with a previously issued client certificate (e.g., an existing
certificate issued by the EST CA);
o TLS with a previously installed certificate (e.g., manufacturer
installed certificate or a certificate issued by some other
party);
o Certificate-less TLS (e.g., with a shared credential distributed
out-of-band);
o HTTP-based with a username/password distributed out-of-band.
2.2.1. Certificate TLS authentication
If the EST client has a previously installed certificate issued by a
third party CA, this certificate can be used to authenticate the
client's request for a certificate from the EST server (if that CA is
recognized by the EST server). An EST client responds to the EST
server's TLS certificate request message with the existing
certificate already held by the client. The EST server will verify
the client's existing certificate and authorize the client's request
as described in Section 3.3.2.
2.2.2. Certificate-less TLS authentication
The EST client and EST server can be mutually authenticated using a
certificate-less TLS cipher suite (see Section 3.3.3).
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2.2.3. HTTP-based client authentication
The EST server can optionally also request that the EST client submit
a username/password using the HTTP Basic or Digest Authentication
methods (see Section 3.2.3). This approach is desirable if the EST
client cannot be authenticated during the TLS handshake (see Section
3.3.2) or the EST server policy requires additional authentication
information. See Section 3.2.3.
2.3. Client Certificate Re-issuance
An EST client can renew/rekey its existing client certificate by
submitting a re-enrollment request to an EST server.
When the current EST client certificate can be used for TLS client
authentication (Section 3.3.2) the client presents this certificate
to the EST server for client authentication. When the to be re-
issued EST client certificate cannot be used for TLS client
authentication, any of the authentication methods used for initial
enrollment can be used.
For example if the client has an alternative certificate issued by
the EST CA that can be used for TLS client authentication, then it
can be used.
The certificate request message includes the same Subject and
SubjectAltName as the current certificate. Name changes are
requested as specified in Section 4.2.2.
2.4. Server Key Generation
The EST client can request a server-generated certificate and key
pair (see Section 4.4).
2.5. Full PKI Request messages
Full PKI Request [RFC5272] messages can be transported via EST using
the Full CMC Request function. This affords access to functions not
provided by the Simple Enrollment functions. Full PKI Request
messages are defined in Sections 3.2 and 4.2 of [RFC5272]. See
Section 4.3 for a discussion of how EST provides a transport for
these messages.
2.6. Certificate Signing Request (CSR) Attributes Request
Prior to sending an enrollment request to an EST server, an EST
client can query the EST server for a set of additional attribute(s)
that the client is requested to use in a subsequent enrollment
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request.
These attributes can provide additional descriptive information that
the EST server cannot access itself, such as the MAC address of an
interface. Alternatively, these attributes can indicate the kind of
enrollment request, such as a specific elliptic curve or a specific
hash function that the client is expected to use when generating the
CSR.
3. Protocol Design and Layering
Figure 2 provides an expansion of Figure 1 describing how the layers
are used. Each aspect is described in more detail in the sections
that follow.
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EST Layering:
Protocols and uses:
+---------------------------------------------------+
| |
| Message types: |
| - "Simple PKI" messages |
| (incorporating proof-of-possession) |
| - CA certificate retrieval |
| - "Full PKI" messages (OPTIONAL) |
| - CSR attribute request (OPTIONAL) |
| - Server-generated key request (OPTIONAL) |
| |
+---------------------------------------------------+
| |
| HTTP: |
| - HTTP headers and URIs for control |
| - Content-Type headers specify message type |
| - Headers for control/error messages |
| - URIs for selecting functions |
| - Basic or Digest authentication (OPTIONAL) |
| |
+---------------------------------------------------+
| |
| TLS for transport security |
| - Authentication of the EST server |
| - Authentication of the EST client (OPTIONAL) |
| - Provides communications integrity |
| and confidentiality |
| - Channel Binding [RFC5929] to link |
| proof-of-identity with message-based |
| proof-of-possession. (OPTIONAL) |
| |
+---------------------------------------------------+
Figure 2
Specifying HTTPS as the secure transport for enrollment messages
introduces two 'layers' to communicate authentication and control
messages: TLS and HTTP.
The TLS layer provides integrity and confidentiality during
transport. The proof-of-identity is supplied by TLS handshake
authentication and optionally also by the HTTP layer headers. The
message type and control/error messages are included in the HTTP
headers.
CMC [RFC5272] Section 3.1 notes that "the Simple PKI Request MUST NOT
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be used if a proof-of-identity needs to be included". Since the TLS
and HTTP layers provide proof-of-identity for EST clients and servers
the Simple PKI message types are used.
The TLS layer certificate exchange provides a method for authorizing
client enrollment requests using existing certificates. Such
certificates may have been issued by the CA (from which the client is
requesting a certificate) or they may have been issued under a
distinct PKI (e.g., an IEEE 802.1AR IDevID [IDevID] credential).
Proof-of-possession (PoP) is a distinct issue from proof-of-identity
and is included in the Simple PKI message type as described in
Section 3.4. A method of linking proof-of-identity and proof-of-
possession is described in Section 3.5.
This document also defines transport for CMC [RFC5272] that complies
with CMC Transport Protocols [RFC5273].
During protocol exchanges different certificates can be used. The
following table provides an informative overview. End-entities MAY
have one or more certificates of each type listed in Figure 3 and use
one or more Trust Anchor databases of each type listed in Figure 4.
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Certificates and their corresponding uses:
+--------------+--------------------+-------------------------------+
| Certificate | Issuer | Use and section references |
+==============+====================+===============================+
| EST server | The CA served by | Presented by the EST server |
| certificate | the EST server | during the TLS handshake |
| | | |
| | | Section 3.3.1 |
+--------------+--------------------+-------------------------------+
| EST server | A CA | Presented by the EST server |
| certificate | authenticatable by | during the TLS handshake |
| | a third-party TA | |
| | e.g., a web server | Section 3.3.1, and |
| | CA | Security Considerations |
+--------------+--------------------+-------------------------------+
| Third-Party | A CA | Presented by the EST client |
| EST client | authenticatable by | to the EST server by clients |
| certificate | a third-party TA | that have not yet enrolled |
| | e.g., a device | |
| | manufacturer | Section 3.3.2 |
+--------------+--------------------+-------------------------------+
| EST client | The CA served by | Presented to the EST server |
| certificate | the EST server | during future EST operations. |
| | | |
| | | Section 3.3.2 |
+--------------+--------------------+-------------------------------+
| End-Entity | The CA served by | Clients can obtain certs |
| certificate | the EST server | that are intended for |
| | | non-EST uses. This includes |
| | | certs that can not be used |
| | | for EST operations. |
| | | |
| | | Section 4.2.3 |
+--------------+--------------------+-------------------------------+
Figure 3
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Trust Anchor databases and their corresponding uses:
+--------------+----------------------------------------------------+
| TA database | Use and section references |
+==============+====================================================+
| EST server | EST servers use this TA database to authenticate |
| Explicit | certificates issued by the EST CA, including EST |
| TA database | client certificates during enroll/re-enroll |
| | operations |
| | |
| | Section 3.3.2 |
+--------------+----------------------------------------------------+
| EST server | EST servers use this TA database to authenticate |
| Implicit | certificates issued by third-party TAs. |
| TA database | e.g., EST client certificates issued by a device |
| | manufacturer |
| | An Implicit TA database can be disabled. |
| | |
| | Section 3.3.2 |
+--------------+----------------------------------------------------+
| EST client | EST clients use this TA database to authenticate |
| Explicit | certificates issued by the EST CA, including EST |
| TA database | server certificates. |
| | |
| | Section 3.1, Section 3.3.1, Section 3.6.1 and |
| | Section 4.1.1 |
+--------------+----------------------------------------------------+
| EST client | EST clients use this trust anchor database to |
| Implicit | authenticate an EST server that uses an externally |
| TA database | issued certificate. |
| | An Implicit TA database can be disabled. |
| | |
| | Section 3.1, Section 3.3.1, Section 3.6.2 |
| | and Security Considerations |
+--------------+----------------------------------------------------+
Figure 4
3.1. Application Layer
The EST client MUST be capable of generating and parsing Simple PKI
messages (see Section 4.2). Generating and parsing Full PKI messages
is OPTIONAL (see Section 4.3). The client MUST also be able to
request CA certificates from the EST server and parse the returned
"bag" of certificates (see Section 4.1). Requesting CSR attributes
and parsing the returned list of attributes is OPTIONAL (see
Section 4.5).
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Details of the EST client application configuration are out of scope
of the protocol discussion but are necessary for understanding the
prerequisites of initiating protocol operations. The EST client is
RECOMMENDED to be configured with TA databases for Section 3.3.1 or
with a secret key for Section 3.3.3. Implementations conforming to
this standard MUST provide the ability to designate Explicit TAs.
For human usability reasons a "fingerprint" of an Explicit TA
database entry can be configured for bootstrapping as discussed in
Section 4.1.1. Configuration of an Implicit TA database, perhaps by
its inclusion within the EST client distribution or available from
the operating system, provides flexibility along with the caveats
detailed in Section 7. Implementations conforming to this standard
MUST provide the ability to disable use of any Implicit TA database.
The EST client is configured with sufficient information to form the
EST server URI. This can be the full operation path segment (e.g.
https://www.example.com/.well-known/est/ or
https://www.example.com/.well-known/est/arbitraryLabel1) or the EST
client can be configured with a tuple composed of the authority
portion of the URI along with the OPTIONAL label (e.g.
"www.example.com:80", "arbitraryLabel1") or just the authority
portion of the URI.
3.2. HTTP Layer
HTTP is used to transfer EST messages. URIs are defined for handling
each media type (i.e., message type) as described in Section 3.2.2.
HTTP is also used for client authentication services when TLS client
authentication is not available, due to lack of a client certificate
suitable for use by TLS (see Section Section 3.2.3). HTTP
authentication can also be used in addition to TLS client
authentication if the EST server wishes additional authentication
information, as noted in Section 2.2.3. Registered media types are
used to convey EST messages as specified in Figure 6.
HTTP 1.1 [RFC2616] and above support persistent connections. As
described in Section 8.1 of that RFC, persistent connections may be
used to reduce network and processing load associated with multiple
HTTP requests. EST does not require or preclude persistent HTTP
connections and their use is out of scope of this specification.
3.2.1. HTTP headers for control
This document profiles the HTTP content-type header (as defined in
[RFC2046], but see Figure 6 for specific values) to indicate the
media type for EST messages and to specify control messages for EST.
The HTTP Status value is used to communicate success or failure of an
EST function. HTTP authentication is used by a client when requested
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by the server.
The media types indicated in the HTTP content-type header indicates
which EST message is being transferred. Media types used by EST are
specified in Section 3.2.4.
3.2.2. HTTP URIs for control
The EST server MUST use the [RFC5785] defined path-prefix of "/.well-
known/" and the registered name of "est". Thus a valid EST server
URI path begins with "https://www.example.com/.well-known/est". Each
EST operation is indicated by a path-suffix that indicates the
intended operation:
Operations and their corresponding URIs:
+------------------------+-----------------+-------------------+
| Operation |Operation Path | Details |
+========================+=================+===================+
| Distribution of CA | /CACerts | Section 4.1 |
| certificates (MUST) | | |
+------------------------+-----------------+-------------------+
| Enrollment of new | /simpleEnroll | Section 4.2. |
| clients (MUST) | | |
+------------------------+-----------------+-------------------+
| Re-Enrollment of | /simpleReEnroll | Section 4.2.2 |
| existing clients (MUST)| | |
+------------------------+-----------------+-------------------+
| Full CMC (OPTIONAL) | /fullCMC | Section 4.3 |
+------------------------+-----------------+-------------------+
| Server-side Key | /serverKeyGen | Section 4.4 |
| Generation (OPTIONAL) | | |
+------------------------+-----------------+-------------------+
| Request CSR attributes | /CSRAttrs | Section 4.5 |
| (OPTIONAL) | | |
+------------------------+-----------------+-------------------+
Figure 5
The operation path (Figure 5) is appended to the path-prefix to form
the URI used with HTTP GET or POST to perform the desired EST
operation. An example valid URI absolute path for the "/CACerts"
operation is "/.well-known/est/CACerts". To retrieve the CA's
certificates, the EST client would use the following HTTP request:
GET /.well-known/est/CACerts HTTP/1.1
Likewise, to request a new certificate in this example scheme, the
EST client would use the following request:
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POST /.well-known/est/simpleEnroll HTTP/1.1
The use of distinct operation paths simplifies implementation for
servers that do not perform client authentication when distributing
/CACerts responses.
An EST server MAY provide service for multiple CAs as indicated by an
OPTIONAL additional path segment between the registered application
name and the operation path. To avoid conflict the CA label MUST NOT
be the same as any defined operation path segment. The EST server
MUST provide services when the additional path segment is not
included. The following are three example valid URIs:
1. https://www.example.com/.well-known/est/CACerts
2. https://www.example.com/.well-known/est/arbitraryLabel1/CACerts
3. https://www.example.com/.well-known/est/arbitraryLabel2/CACerts
In this specification the distinction between enroll and renew/rekey
is explicitly indicated by the HTTP URI. When requesting /fullCMC
operations CMC uses the same messages for certificate renewal and
certificate rekey.
An EST server MAY provide additional services using other URIs.
3.2.3. HTTP-Based Client Authentication
The EST server MAY request HTTP-based client authentication. This
request can be in addition to successful TLS client authentication
(Section 3.3.2) if EST server policy requires additional
authentication. (For example the EST server may require that an EST
client "knows" a password in addition to "having" an existing client
certificate). Or HTTP-based client authentication can be an EST
server policy specified fallback in situations where the EST client
did not successfully complete the TLS client authentication. (This
might arise if the EST client is enrolling for the first time or if
the certificates available to an EST client cannot be used for TLS
client authentication).
HTTP Basic and Digest authentication MUST only be performed over TLS
1.1 [RFC4346] or later versions. As specified in CMC: Transport
Protocols [RFC5273] the server "MUST NOT assume client support for
any type of HTTP authentication such as cookies, Basic
authentication, or Digest authentication". Clients SHOULD support
the Basic and Digest authentication mechanism.
Servers that wish to use Basic and Digest authentication reject the
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HTTP request using the HTTP defined WWW-Authenticate response-header
([RFC2616], Section 14.47). The client is expected to retry the
request, including the appropriate Authorization Request Header
([RFC2617], Section 3.2.2), if the client is capable of using the
Basic or Digest authentication. If the client is not capable of
retrying the request or it is not capable of Basic or Digest
authentication, then the client MUST terminate the connection.
A client MAY set the username to the empty string ("") if it is
presenting a password that is not associated with a username.
Support for HTTP-based client authentication has security
ramifications as discussed in Section 7. The client MUST NOT respond
to the server's HTTP authentication request unless the client has
authenticated the EST server (as per Section 3.6).
3.2.4. Message types
This document uses existing media types for the messages as specified
by [RFC2585], [RFC5967], and CMC [RFC5272]. To support distribution
of multiple certificates for a CA certificate path, the [RFC2046]
multipart/mixed media type is used.
For consistency with [RFC5273], each distinct EST message type uses
an HTTP Content-Type header with a specific media type.
The EST messages and their corresponding media types are:
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+--------------------+--------------------------+-------------------+
| Message type |Request media type | Request section(s)|
| |Response media type(s) | Response section |
| |Source(s) of types | |
+====================+==========================+===================+
| CA certificate | N/A | Section 4.1 |
| request | application/pkcs7-mime | Section 4.1.1 |
| | [RFC5751] | |
+--------------------+--------------------------+-------------------+
| Cert enroll/renew/ | application/pkcs10 | Section 4.2/4.2.1 |
| rekey | application/pkcs7-mime | Section 4.2.2 |
| | [RFC5967] [RFC5751] | |
+--------------------+--------------------------+-------------------+
| Full CMC | application/pkcs7-mime | Section 4.3.1 |
| | application/pkcs7-mime | Section 4.3.2 |
| | [RFC5751] | |
+--------------------+--------------------------+-------------------+
| Server-side Key | application/pkcs10 | Section 4.4.1 |
| Generation | multipart/mixed | Section 4.4.2 |
| | (application/pkcs7-mime &| |
| | application/pkcs8) | |
| | [RFC5967] [RFC5751] & | |
| | [RFC5958] | |
+--------------------+--------------------------+-------------------+
| Request CSR | N/A | Section 4.5.1 |
| attributes | application/csrattrs | Section 4.5.2 |
| | This RFC | |
+--------------------+--------------------------+-------------------+
Figure 6
3.3. TLS Layer
TLS provides authentication, which in turn enables authorization
decisions. The EST server and EST client are responsible for
ensuring that an acceptable cipher suite is negotiated and that
bidirectional authentication has been performed. Alternately,
certificate-less TLS authentication, where neither the client nor
server present a certificate, is also an acceptable method for EST
mutual authentication.
HTTPS [RFC2818] specifies how HTTP messages are carried over TLS.
HTTPS MUST be used. TLS 1.1 [RFC4346] (or a later version) MUST be
used TLS session resumption [RFC5077] SHOULD be supported.
TLS channel binding information MAY be inserted into a certificate
request as detailed in Section 3.5 in order to provide the EST server
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with assurance that the authenticated TLS client has access to the
private key for the certificate being requested.
3.3.1. TLS-Based Server Authentication
The EST server MUST be authenticated during the TLS handshake unless
the client is requesting Bootstrap Distribution of CA certificates
(Section 4.1.1) or Full CMC (Section 4.3).
The EST client authenticates the EST server as defined for the cipher
suite negotiated. The following text provides details assuming a
certificate-based cipher suite, such as the TLS 1.1 [RFC4346]
mandatory cipher suite (TLS_RSA_WITH_3DES_EDE_CBC_SHA). As an
alternative to authentication using a certificate, an EST client MAY
support certificate-less TLS authentication (Section 3.3.3).
Certificate validation MUST be performed as per [RFC5280]. The EST
server certificate MUST conform to the [RFC5280] certificate profile.
The client validates the TLS server certificate using the EST client
Explicit and, if enabled, Implicit TA database(s). The client MUST
maintain a distinction between the use of Explicit and Implicit TA
databases during authentication in order to support proper
authorization. The EST client MUST perform authorization checks as
specified in Section 3.6.
If certificate validation fails, the client MAY follow the procedure
outlined in Section 4.1.1 for bootstrap distribution of CA
certificates.
3.3.2. TLS-Based Client Authentication
TLS client authentication is the RECOMMENDED method for identifying
EST clients. HTTP-Based Client Authentication (Section 3.2.3) MAY be
used.
The EST server authenticates the EST client as defined for the cipher
suite negotiated. The following text provides details assuming a
certificate-based cipher suite such as the TLS 1.1 [RFC4346]
mandatory cipher suite (TLS_RSA_WITH_3DES_EDE_CBC_SHA). The EST
server MUST support certificate based client authentication. As an
alternative or as an addition to authentication using a certificate,
an EST server MAY support certificate-less TLS authentication
(Section 3.3.3).
Generally, the client will use an existing certificate for renew or
rekey operations. If the certificate to be renewed or rekeyed is
appropriate for the negotiated cipher suite, then the client MUST use
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it for the TLS handshake, otherwise the client SHOULD use an
alternate certificate that is suitable for the cipher suite and
contains the same subject identity information. When requesting an
enroll operation the client MAY use a third-party issued client
certificate to authenticate itself.
Certificate validation MUST be performed as per [RFC5280]. The EST
client certificate MUST conform to the [RFC5280] certificate profile.
The server validates the TLS server certificate using the EST server
Explicit and, if enabled, Implicit TA database(s). The server MUST
maintain a distinction between the use of Explicit and Implicit TA
databases during authentication in order to support proper
authorization.
The EST server MUST perform authorization checks as specified in
Section 3.7.
If a client does not support TLS client authentication, then it MUST
support HTTP-based client authentication (Section 3.2.3) or
certificate-less TLS authentication (Section 3.3.3).
3.3.3. Certificate-less TLS Mutual Authentication
Certificate-less TLS cipher suites provide a way to perform mutual
authentication in situations where neither the client nor server have
certificates, do not desire to use certificates, or do not have the
trust anchors necessary to verify a certificate. The client and
server MAY negotiate a certificate-less cipher suite for mutual
authentication.
When using certificate-less mutual authentication in TLS for
enrollment, the cipher suite MUST be based on a protocol that is
resistant to dictionary attack and MUST be based on a zero knowledge
protocol. TLS-SRP ciphersuites listed in section 2.7 of [RFC5054]
are suitable for this purpose. Section 7 lists the characteristics
of a ciphersuite that are suitable for use in certificate-less mutual
authentication for enrollment.
Successful authentication using a certificate-less cipher suite
proves knowledge of a pre-shared secret which implicitly authorizes a
peer in the exchange.
3.4. Proof-of-Possession
As defined in Section 2.1 of CMC [RFC5272], Proof-of-possession (POP)
"refers to a value that can be used to prove that the private key
corresponding to the public key is in the possession and can be used
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by an end-entity."
The signed enrollment request provides a signature-based proof-of-
possession. The mechanism described in Section 3.5 strengthens this
by optionally including "Direct"-based proof-of-possession [RFC5272]
by including TLS session-specific information within the data covered
by the enrollment request signature (thus linking the enrollment
request to the authenticated end-point of the TLS connection).
3.5. Linking Identity and PoP information
Server policy will determine whether the server requires the
mechanism specified in this section be used by the client. This
specification provides an OPTIONAL method of linking identity and
proof-of-possession by including information specific to the current
authenticated TLS session within the signed certification request.
The client can determine if the server requires the linking of
identity and PoP by examining the CSR Attributes Response (see
Section 4.5.2). Regardless of the CSR Attributes Response, clients
are RECOMMENDED to link identity and PoP by embedding tls-unique
information in the certification request. If tls-unique information
is included by the client, the server MUST verify it. The EST server
MAY reject requests without tls-unique information as indicated by
server policy.
Linking identity and proof-of-possession proves to the server that
the authenticated TLS client has possession of the private key
associated with the certification request and that the client was
able to sign the certification request after the TLS session was
established. This is an alternative to the [RFC5272] Section 6.3-
defined "Linking Identity and POP information" method available if
Full PKI messages are used.
The client generating the request obtains the tls-unique value as
defined in Channel Bindings for TLS [RFC5929] from the TLS subsystem.
The tls-unique specification includes a synchronization problem as
described in Channel Bindings for TLS [RFC5929] section 3.1. To
avoid this problem, EST implementations that support this feature
MUST use the tls-unique value from the first TLS handshake. EST
clients and servers use their tls-unique implementation specific
synchronization methods to obtain this first tls-unique value. TLS
"secure_renegotiation" [RFC5746] MUST be used. This maintains the
binding from the first tls-unique value across renegotiations to the
most recently negotiated connection.
The tls-unique value is base 64-encoded as specified in Section 4 of
[RFC4648] and the resulting string is placed in the certification
request challenge-password field ([RFC2985], Section 5.4.1). If tls-
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unique information is not embedded within the certification request
the challenge-password field MUST be empty to indicate that the
client did not include the optional channel-binding information (any
value submitted is verified by the server as tls-unique information).
If the EST server makes use of a back-end infrastructure for
processing, it is RECOMMENDED that the results of this verification
be communicated. (For example this communication might use the CMC
"RA POP Witness Control" in a CMC Full PKI Request message. Or an
EST server might TLS authenticate an EST client as being a trusted
infrastructure element that does not forward invalid requests. A
detailed discussion of back-end processing is out of scope).
When rejecting requests, the EST server response is as described for
all enroll responses (Section 4.2.3). If a Full PKI Response is
included, the CMCFailInfo MUST be set to popFailed. If a human
readable reject message is included it SHOULD include an informative
text message indicating that linking of identity and POP information
is required.
3.6. Server Authorization
The client MUST check EST server authorization before accepting any
server responses or responding to HTTP authentication requests.
The EST client authorization method depends on which method was used
to authenticate the server. When the Explicit TA database is used to
authenticate the EST server then Section 3.6.1 applies. When the
Implicit TA database is used to authenticate the EST server then
Section 3.6.2 applies. Successful authentication using a
certificate-less cipher suite implies authorization of the server.
The client MAY perform bootstrapping as specified in Section 4.1.1
even if these checks fail.
3.6.1. Client use of Explicit TA Database
When the EST client Explicit TA database is used to validate the EST
server certificate the client MUST check either the configured URI
against the server's identity, or the EST server certificate MUST
contain the id-kp-cmcRA [RFC6402] extended key usage extension.
3.6.2. Client use of Implicit TA Database
When the EST client Implicit TA database is used to validate the EST
server certificate, the client MUST check the URI "against the
server's identity as presented in the server's Certificate message"
(HTTP Over TLS Section 3.1 "Server Identity" [RFC2818] and
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[RFC6125]). The provisioned URI provides the basis for
authorization, and the server's authenticated identity confirms it is
the authorized server.
3.7. Client Authorization
The decision to issue a certificate to a client is always controlled
by local CA policy. The EST server configuration reflects this CA
policy. This document does not specify any constraints on such
policy. EST provides the EST server access to each client's
authenticated identity -- e.g., the TLS client's certificate in
addition to any HTTP user authentication credentials -- to help in
implementing such policy.
If the client's certificate was issued by the EST CA, and it includes
the id-kp-cmcRA [RFC6402] extended key usage extension, then the
client is a Registration Authority (RA) as described in [RFC5272] and
[RFC6402]. In this case the EST server SHOULD apply authorization
policy consistent with an RA client. For example when handling
/simpleEnroll requests the EST server could be configured to accept
PoP linking information that does not match the current TLS session
because the authenticated EST client RA has verified this information
when acting as an EST server (as specified in Section 3.5). More
specific RA mechanisms are available if the EST client uses /fullCMC
methods.
4. Protocol Exchange Details
Before processing a request, an EST server determines if the client
is authorized to receive the requested services. Likewise, the
client determines if it will make requests to the EST server. These
authorization decisions are described in the next two sections.
Assuming that both sides of the exchange are authorized, then the
actual operations are as described in subsequent sections.
4.1. Distribution of CA certificates
The EST client can request a copy of the current CA certificates.
This function is generally performed before other EST functions.
4.1.1. Bootstrap Distribution of CA certificates
It is possible that the client was not configured with the TA
database(s) necessary to validate the EST server certificate. This
section describes a method by which minimally configured EST clients
can populate their Explicit TA database.
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If the EST client application does not specify either an Explicit TA
database or a Implicit TA database then the initial TLS server
authentication and authorization will fail. The client MAY
provisionally continue the TLS handshake to completion for the
purposes of accessing the /CACerts or /fullCMC method. If the EST
client continues with an unauthenticated connection, the client MUST
extract the HTTP content data from the response (Section 4.1.3 or
Section 4.3.2) and engage a human user to authorize the CA
certificate using out-of-band data such as a CA certificate
"fingerprint" (e.g., a SHA-256 or SHA-512 [SHS] hash on the whole CA
certificate). In a /fullCMC response it is the Publish Trust Anchors
control within the Full PKI Response that must be accepted manually.
It is incumbent on the user to properly verify the TA information, or
to provide the "fingerprint" data during configuration that is
necessary to verify the TA information.
HTTP authentication requests MUST NOT be responded to if the server
has not been authenticated.
The EST client uses the /CACerts response to establish an Explicit
Trust Anchor database for subsequent TLS authentication of the EST
server. EST clients MUST NOT engage in any other protocol exchange
until after the /CACerts response has been accepted and a new TLS
session has been established (using TLS certificate-based
authentication).
4.1.2. CA certificates request
EST clients request the EST CA TA database information of the CA (in
the form of certificates) with an HTTPS GET message using an
operation path of "/CACerts". EST clients and servers MUST support
the /CACerts function. Clients SHOULD request an up-to-date response
before stored information has expired in order to ensure the EST CA
TA database is up to date.
The EST server MUST NOT require client authentication or
authorization to reply to this request.
The client MUST authenticate the EST server as specified in
Section 3.3.1 and Section 3.3.3 and check the server's authorization
as given in Section 3.6 or follow the procedure outlined in
Section 4.1.1.
4.1.3. CA certificates response
If successful, the server response MUST have an HTTP 200 response
code. Any other response code indicates an error and the client MUST
abort the protocol.
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A successful response MUST be a certs-only CMC Simple PKI Response,
as defined in [RFC5272], containing the certificates described in the
following paragraph. The HTTP content-type of "application/
pkcs7-mime" is used. The Simple PKI response is sent with a Content-
Transfer-Encoding of "base64" [RFC2045].
The EST server MUST include the current root CA certificate in the
response. The EST server MUST include any additional certificates
the client would need to build a chain from an EST CA issued
certificate to the current EST CA TA. For example if the EST CA is a
subordinate CA then all the appropriate subordinate CA certificates
necessary to build a chain to the root EST CA are included in the
response.
The EST server SHOULD include the three "Root CA Key Update"
certificates OldWithOld, OldWithNew, and NewWithOld in the response
chain. These are defined in Section 4.4 of CMP [RFC4210]. The EST
client MUST be able to handle these certificates in the response.
The EST CA's most recent self-signed certificate (e.g. NewWithNew
certificate) is self-signed and has the latest NotAfter date. If the
EST server does not include these in the response then after the
current EST CA certificate expires the EST clients will need to be
reinitialized with the PKI using the Bootstrap Distribution of CA
certificates (Section 4.1.1) method, which involves user interaction.
After out-of-band validation occurs, all the other certificates MUST
be validated using normal [RFC5280] certificate path validation
(using the most recent CA certificate as the TA) before they can be
used to build certificate paths during certificate validation.
The EST client MUST store the extracted EST CA certificate as an
Explicit TA database entry for subsequent EST server authentication.
The EST client SHOULD disable use of Implicit TA database entries for
this EST server, now that an Explicit TA database entry is available.
If the client disables the Implicit TA database, and if the EST
server certificate was verified using an Implicit TA database entry,
then the client MUST include the "Trusted CA Indication" extension in
future TLS sessions [RFC4366]. This indicates to the server that
only an EST Server certificate authenticatable by the Explicit TA
database entry is now acceptable (otherwise the EST server might
continue to use a server certificate that is only verifiable by a now
disabled Implicit TA).
The EST client SHOULD also make the CA Certificate response
information available to the end-entity software for use when
validating peer certificates.
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4.2. Client Certificate Request Functions
EST clients request a certificate from the EST server with an HTTPS
POST using the operation path value of "/simpleEnroll". EST clients
request a renew/rekey of existing certificates with an HTTP POST
using the operation path value of "/simpleReEnroll". EST servers
MUST support the /simpleEnroll and /simpleReEnroll functions.
It is RECOMMENDED that a client obtain the current CA certificates,
as described in Section 4.1, before performing certificate request
functions. This ensures that the client will be able to validate the
EST server certificate. The client MUST authenticate the EST server
as specified in Section 3.3.1 and Section 3.3.3. The client MUST
verify the authorization the EST server as specified in Section 3.6.
The server MUST authenticate the client as specified in Section 3.3.2
and Section 3.3.3. The server MUST verify client authorization as
specified in Section 3.7. The EST server MUST check the tls-unique
value as described in Section 3.5 if one is submitted by the client.
The server MAY accept a certificate request for manual authorization
checking by an administrator. (Section 4.2.3 describes the use of an
HTTP 202 response to the EST client if this occurs).
4.2.1. Simple Enrollment of Clients
When HTTPS POSTing to /simpleEnroll the client MUST include a Simple
PKI Request as specified in CMC Section 3.1 (i.e., a PKCS#10
Certification Request).
The Certification Signing Request (CSR) signature provides proof-of-
possession of the private key to the EST server. If the CSR KeyUsage
extension indicates the private key can be used to generate digital
signatures then the CSR signature MUST be generated using the private
key. If the key can be used to generate digital signatures but the
requested CSR KeyUsage extension prohibits generation of digital
signatures then the CSR signature MUST still be generated using the
private key but the key MUST NOT be used to for any other signature
operations (this is consistent with the recommendations concerning
submission of proof-of-possession to an RA or CA as described in
[SP-800-57-Part-1]). The use of /fullCMC operations provides access
to more advanced proof-of-possession methods that MUST be used when
the key pair can not be used for digital signature generation (see
Section 4.3).
The HTTP content-type of "application/pkcs10" is used here. The
format of the message is as specified in [RFC5967] with a Content-
Transfer-Encoding of "base64" [RFC2045].
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The EST client MAY request additional certificates even when using an
existing certificate in the TLS client authentication. For example
the client can use an existing certificate for TLS client
authentication when requesting a certificate that cannot be used for
TLS client authentication.
4.2.2. Simple Re-Enrollment of Clients
EST clients renew/rekey certificates with an HTTPS POST using the
operation path value of "/simpleReEnroll".
A certificate request employs the same format as the "simpleEnroll"
request, using the same HTTP content-type. The request Subject field
and SubjectAltName extension MUST be identical to the corresponding
fields in the certificate being renewed/rekeyed. The
ChangeSubjectName attribute, as defined in [RFC6402], MAY be included
in the CSR to request that these fields be changed in the new
certificate.
If the Subject Public Key Info in the certification request is the
same as the current client certificate, the EST server performs a
renew operation. If the public key information is different than the
currently issued certificate then the EST server performs a rekey
operation.
4.2.3. Simple Enroll and Re-Enroll Response
If the enrollment is successful, the server response MUST contain an
HTTP 200 response code with a content-type of "application/
pkcs7-mime".
A successful response MUST be a certs-only CMC Simple PKI Response,
as defined in [RFC5272], containing only the certificate that was
issued. The HTTP content-type of "application/pkcs7-mime" is used.
The Simple PKI response is sent with a Content-Transfer-Encoding of
"base64" [RFC2045].
When rejecting a request the server MUST specify either an HTTP 4xx
error, or an HTTP 5xx error. A Simple PKI Response with an HTTP
content-type of "application/pkcs7-mime" (see Section 4.3.2) MAY be
included in the response data to convey an error response. If the
content-type is not set the response data MUST be a plain text human-
readable error message containing informative information describing
why the request was rejected (for example indicating that CSR
attributes are incomplete).
If the server responds with an HTTP [RFC2616] 202, this indicates
that the request has been accepted for processing but that a response
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is not yet available. The server MUST include a Retry-After header
as defined for HTTP 503 responses. The server also MAY include
informative human-readable content. The client MUST wait at least
the specified 'retry-after' time before repeating the same request.
The client repeats the initial enrollment request after the
appropriate 'retry-after' interval has expired. The client SHOULD
log or inform the end user of this event. The server is responsible
for maintaining all state necessary to recognize and handle retry
operations as the client is stateless in this regard; it simply sends
the same request repeatedly until it receives a different response
code.
All other return codes are handled as specified in HTTP [RFC2616].
The EST client MAY also make the certificate response, and associated
private key, available to end-entity software for use as an end-
entity certificate.
4.3. Full CMC
An EST client can request a certificate from an EST server with an
HTTPS POST using the operation path value of "/fullCMC". Support for
the /fullCMC function is OPTIONAL for both clients and servers.
4.3.1. Full CMC Request
If the HTTP POST to /fullCMC is not a valid Full PKI Request, the
server MUST reject the message. The HTTP content-type used is
"application/pkcs7-mime", as specified in [RFC5273]. The body of the
message is the binary value of the encoding of the PKI Request with a
Content-Transfer-Encoding of "base64" [RFC2045].
4.3.2. Full CMC Response
If the enrollment is successful, the server response MUST include an
HTTP 200 response code with a content-type of "application/
pkcs7-mime" as specified in [RFC5273]. The response data includes
either the Simple PKI Response or the Full PKI Response as specified
in Section 3.2 of [RFC5272]. The body of the message is the binary
value of the encoding of the PKI Response with a Content-Transfer-
Encoding of "base64" [RFC2045].
When rejecting a request, the server MUST specify either an HTTP 4xx
error or an HTTP 5xx error. A CMC response with content-type of
"application/pkcs7-mime" SHOULD be included in the response data for
any CMC error response. If the content-type is not set the response
data MUST be a plain text human-readable error message containing
informative information describing why the request was rejected (for
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example indicating that CSR attributes are incomplete).
All other return codes are handled as specified in Section 4.2.3 or
HTTP [RFC2616]. For example, a client interprets an HTTP 404 or 501
response to indicate that this service is not implemented.
4.4. Server-side Key Generation
An EST client may request a private key and associated certificate
from an EST server using an HTTPS POST with an operation path value
of "/serverKeyGen". Support for the /serverKeyGen function is
OPTIONAL.
A client MUST authenticate and authorize an EST server as specified
in Section 3.3.1, Section 3.6, and Section 3.3.3.
The EST server MUST authenticate and authorize the client as
specified in Section 3.3.2, Section 3.7, and Section 3.3.3. The EST
server applies whatever authorization or logic it chooses to
determine if the private key and certificate should be provided.
Proper random number and key generation [RFC4086] is a server
implementation responsibility and server storage of generated keys is
a local option. The key pair and certificate are transferred over
the TLS session. The cipher suite used to return the private key and
certificate MUST offer confidentiality commensurate with the private
key being delivered to the client.
The EST client MAY request additional certificates even when using an
existing certificate in the TLS client authentication. For example
the client can use an existing certificate for TLS client
authentication when requesting a certificate that cannot be used for
TLS client authentication.
4.4.1. Server-side Key Generation Request
The certificate request is HTTPS POSTed and is the same format as for
the "/simpleEnroll" and "/simpleReEnroll" path extensions with the
same content-type and transfer encoding.
In all respects the server SHOULD treat the CSR as it would any
enroll or re-enroll CSR; the only distinction here is that the server
MUST ignore the public key values and signature in the CSR. These
are included in the request only to allow re-use of existing
codebases for generating and parsing such requests.
If the client desires to receive the private key with encryption that
exists outside and in addition to that of the TLS transport used by
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EST or if server policy requires that the key be delivered in such a
form, the client MUST include an attribute in the CSR indicating the
encryption key to be used. Both symmetric and asymmetric encryption
are supported as described in the following subsections.
4.4.1.1. Requests for Symmetric Key Encryption of the Private Key
To specify a symmetric encryption key to be used to encrypt the
server-generated private key, the client MUST include a
DecryptKeyIdentifier attribute (as defined in Section 2.2.5,
[RFC4108]) specifying the identifier of the secret key to be used by
the server to encrypt the private key. While that attribute was
originally designated for specifying a firmware encryption key, it
exactly mirrors the requirements for specifying a secret key to
encrypt a private key. If the server does not have a secret key
matching the identifier specified by the client, the request must be
terminated and an error returned to the client. Distribution of the
key specified by the DecryptKeyIdentifer to the key generator and the
client is outside the scope of this document.
4.4.1.2. Requests for Asymmetric Encryption of the Private Key
To specify an asymmetric encryption key to be used to encrypt the
server-generated private key, the client MUST include an
AsymmetricDecryptKeyIdentifier attribute. The
AsymmetricDecryptKeyIdentifier attribute is defined as:
id-aa-asymmDecryptKeyID OBJECT IDENTIFIER ::= {
id-pkix TBD }
The asymmetric-decrypt-key-identifier attribute values have ASN.1
type AsymmetricDecryptKeyIdentifier:
AsymmetricDecryptKeyIdentifier ::= OCTET STRING
If the server does not have a public key matching the identifier
specified by the client, the request must be terminated and an error
returned to the client. Distribution of the key specified by the
AysmmetricDecryptKeyIdentifer to the key generator and the client is
outside the scope of this document.
4.4.2. Server-side Key Generation Response
If the request is successful, the server response MUST have an HTTP
200 response code with a content-type of "multipart/mixed" consisting
of two parts. One part is the private key data and the other part is
the certificate data.
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The format in which the private key data part is returned is
dependent on whether the private key is being returned with
additional encryption on top of that provided by TLS.
If additional encryption is not being employed, the private key data
MUST be placed in an "application/pkcs8". An "application/pkcs8"
part consists of the base 64-encoded DER-encoded PrivateKeyInfo with
a Content-Transfer-Encoding of "base64" [RFC2045].
If additional encryption is being employed, the private key is placed
inside of a CMS SignedData. The SignedData is signed by the party
that generated the private key, which may or may not be the EST
server or the EST CA. The SignedData is further protected inside of
a CMS EnvelopedData, as described in Section 4 of [RFC5958]. The
following list shows how the EncryptedData is used, depending on the
type of protection key specified by the client.
o If the client specified a symmetric encryption key to protect the
server-generated private key, the EnvelopedData content is
encrypted using the secret key identified in the request. The
EnvelopedData RecipientInfo field MUST indicate the ori (Other
Recipient Info) key management technique. The oriType will be
set to TBD and the oriValue will be set to TBD.
o If the client specified an asymmetric encryption key suitable for
key transport operations to protect the server-generated private
key, the EnvelopedData content is encrypted using a randomly-
generated symmetric encryption key. The cryptographic strength
of the symmetric encryption key SHOULD be equivalent to the
client-specified asymmetric key. The EnvelopedData RecipientInfo
field MUST indicate the ktri (KeyTransRecipientInfo) key
management technique. The KeyTransRecipInfo carries the random
symmetric encryption key wrapped in the asymmetric key. The rid
(recipient identification) field in the KeyTransRecipInfo MUST be
ignored by the client.
o If the client specified an asymmetric encryption key suitable for
key agreement operations to protect the server-generated private
key, the EnvelopedData content is encrypted using a randomly-
generated symmetric encryption key. The cryptographic strength
of the symmetric encryption key SHOULD be equivalent to the
client-specified asymmetric key. The EnvelopedData RecipientInfo
field MUST indicate the kari (KeyAgreeRecipientInfo) key
management technique. The RecipientEncryptedKey carries the
random symmetric encryption key encrypted in the key derived from
the key agreement process. The rid (recipient identification)
field in the RecipientEncryptedKey field and the
KeyAgreeRecipientIdentifier field MUST be ignored by the client.
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In all three additional encryption cases, the EnvelopedData is
returned in the response as an "application/pkcs7-mime" part with a
Content-Transfer-Encoding of "base64".
The certificate data part is an "application/pkcs7-mime" and exactly
matches the certificate response to /simpleEnroll. If both parts are
"application/pkcs7-mime" the client checks each; one will be a certs-
only Simple PKI response and the other will be the CMS message with
the encrypted data.
When rejecting a request, the server MUST specify either an HTTP 4xx
error, or an HTTP 5xx error. If the content-type is not set, the
response data MUST be a plain text human-readable error message.
4.5. CSR Attributes
CA policy may allow inclusion of client-provided attributes in
certificates that it issues, and some of these attributes may
describe information that is not available to the CA. In addition, a
CA may desire to certify a certain type of public key and a client
may not have a priori knowledge of that fact. Therefore, clients
SHOULD request a list of expected attributes that are required, or
desired, by the CA in an enrollment request, or if dictated by local
policy.
Requesting CSR Attributes is optional but clients are advised that
CA's may refuse enrollment requests that are not encoded according to
the CA's policy.
4.5.1. CSR Attributes Request
The EST client requests a list of CA-desired CSR attributes from the
CA by sending an HTTPS GET message to the EST server with an
operations path of "/CSRAttrs".
4.5.2. CSR Attributes Response
If locally configured policy for an authenticated EST client
indicates a CSR Attributes Response is to be provided, the server
response MUST include an HTTP 200 response code. An HTTP response
code of 204 or 404 indicates that a CSR Attributes Response is not
available. Regardless of the response code, the EST server and CA
MAY reject any subsequent enrollment requests for any reason, e.g.,
incomplete CSR attributes in the request.
If the CA requires a particular crypto system (e.g., certification of
a public key based on a certain elliptic curve) it MUST provide that
information in the CSR Attributes response. If an EST server
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requires the linking of identity and PoP information (see
Section 3.5) it MUST include the challengePassword OID in the CSR
Attributes response.
Responses to attribute request messages MUST be encoded as content-
type of "application/csrattrs" with a Content-Transfer-Encoding of
"base64" [RFC2045]. The syntax for application/csrattrs body is as
follows:
Csrattrs ::= SEQUENCE SIZE (0..MAX) OF OBJECT IDENTIFIER { }
An EST server includes zero or more object identifiers that it
requests the client to include in a certification request. When the
server encodes Csrattrs as an empty SEQUENCE it means that the server
has no specific additional attributes it requests in a client
certification request (this is functionally equivalent to an HTTP
response code of 204 or 404.) The sequence is Distinguished Encoding
Rules (DER) encoded and then base 64 encoded (section 4 of
[RFC4648]). The resulting text forms the application/csrattr body,
without headers.
For example, if a CA requests a client to submit a certification
request containing the Media Access Control (MAC) address [RFC2397]
of a device, the challengePassword (indicating that Linking of
Identity and POP information is requested, see Section 3.5), to use
the the secp384r1 elliptic curve, and to use the SH384 hash function
then it sends the following object identifiers:
o macAddress: 1.3.6.1.1.1.1.22
o challengePassword: 1.2.840.113549.1.9.7
o the secp384r1 elliptic curve: 1.3.132.0.34
o the SHA384 hash function: 2.16.840.1.101.3.4.2.2
and encodes them into an ASN.1 SEQUENCE to produce:
30 26 06 07 2B 06 01 01 01 01 16 06 09 2A 86 48 86 F7 0D 01 09 07
06 05 2B 81 04 00 22 06 09 60 86 48 01 65 03 04 02 02
and then base 64 encodes the resulting ASN.1 SEQUENCE to produce:
MCYGBysGAQEBARYGCSqGSIb3DQEJBwYFK4EEACIGCWCGSAFlAwQCAg==
The EST client parses the OID's in the response and handles each OID
independently. When an OID indicates a known descriptive CSR
attribute type, the client SHOULD include the requested information
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in the subsequent CSR that it submits, either in the CSR attributes
or in any other appropriate CSR field. When an OID indicates a
particular way to generate the CSR, the client SHOULD generate its
CSR according to the parsed OID. When an OID is of an unknown type
the OID MUST be ignored by the client.
5. Contributors/Acknowledgements
The editors would like to thank Stephen Kent, Vinod Arjun, Jan
Vilhuber, Sean Turner, Russ Housley, and others for their feedback
and prototypes of early drafts. Our thanks also go the authors of
[RFC6403] around whose document we structured part of this
specification.
6. IANA Considerations
There is one OID in Section 4.4.1.2 that needs to be registered in
the PKIX Arc.
IANA is requested to register the following:
IANA SHALL update the well-known URI registry with the following
filled-in template from [RFC5785].
URI suffix: est
Change controller: IETF
IANA SHALL update the Application Media Types registry with the
following filled-in template from [RFC4288].
The media subtype for Attributes in a CertificationRequest is
application/csrattrs.
Type name: application
Subtype name: csrattrs
Required parameters: None
Optional parameters: None
Encoding considerations: binary;
Security Considerations:
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Clients request a list of attributes that servers wish to be in
certification requests. The request/response SHOULD be done in
a TLS-protected tunnel.
Interoperability considerations: None
Published specification: This memo.
Applications which use this media type:
Enrollment over Secure Transport (EST)
Additional information:
Magic number(s): None
File extension: None
Macintosh File Type Code(s):
Person & email address to contact for further information:
Dan Harkins <dharkins@arubanetworks.com>
Restrictions on usage: None
Author: Dan Harkins <dharkins@arubanetworks.com>
Intended usage: COMMON
Change controller: The IESG
7. Security Considerations
Support for Basic authentication as specified in HTTP [RFC2617]
allows the server access to a client's cleartext password. This
provides support for legacy username/password databases but requires
exposing the plaintext password to the EST server. Use of a PIN or
one-time-password can help mitigate such exposure, but it is
RECOMMENDED that EST clients use such credentials only once to obtain
a client certificate (that will be used during future interactions
with the EST server).
When a client uses the Implicit TA database for certificate
validation (see Section 3) then authorization proceeds as specified
in Section 3.6.2. In this situation, the client has validated the
server as being a certified-by-a-third-party responder for the URI
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configured, but cannot verify that the responder is authorized to act
as an RA for the PKI in which the client is trying to enroll.
Clients using an implicit trust anchor database are RECOMMENDED to
only use TLS-based client authentication (to prevent exposing HTTP-
based Client Authentication information). It is RECOMMENDED that
such clients include "Linking Identity and POP information"
(Section 3.5) in requests (to prevent such requests from being
forwarded to a real EST server by a MITM). It is RECOMMENDED that
the implicit trust anchor database used for EST server authentication
be carefully managed, to reduce the chance of a third-party CA with
poor certification practices from being trusted. Disabling the
implicit trust anchor database after succesfully recieving the
Distribution of CA Certificates response (Section 4.1.3) limits any
vulnerability to the first TLS enchange.
Certificate-less TLS ciphersuites that maintain security and perform
the mutual authentiation necessary for enrollment have the following
properties:
o the only information leaked by an active attack is whether a
single guess of the secret is correct or not.
o any advantage an adversary gains is through interaction and not
compuation.
o it is possible to perform countermeasures, such as exponential
backoff after a certain number of failed attempts, to frustrate
repeated active attacks.
Using a certificate-less ciphersuite that does not have the
properties listed above would render the results of enrollment void
and potentially result in certificates being issued to
unauthenticated and/or unauthorized entities.
When using a certificate-less TLS cipher suite, the shared secret
used for authentication and authorization cannot be shared with an
entity that is not a party to the exchange: someone other than the
client and the server. Any additional sharing of secrets voids the
security afforded by a certificate-less cipher suite. Exposure of a
shared secret used by a certificate-less cipher suite to a third-
party enables client impersonation that can results in corruption of
a client's trust anchor database.
As described in CMC Section 6.7, "For keys that can be used as
signature keys, signing the certification request with the private
key serves as a POP on that key pair". The inclusion of tls-unique
within the certification request links the proof-of-possession to the
TLS proof-of-identity by enforcing that the POP operation occurred
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while the TLS session was active. This implies to the server that
the authenticated client currently has access to the private key. If
the authenticated client is known to have specific capabilities, such
as hardware protection for authentication credentials and key
storage, this implication is strengthened but not proven.
The server-side key generation method allows keys to be transported
over the TLS connection to the client. The distribution of private
key material is inherently risky. Private key distribution uses the
encryption mode of the negotiated TLS cipher suite. Keys are not
protected by preferred key wrapping methods such as AES Key Wrap
[RFC3394] or as specified in [RFC5958] as encryption of the private
key beyond that provided by TLS is optional. It is RECOMMEND that
EST servers not support this operation by default. It is RECOMMENDED
that clients not request this service unless there is a compelling
operational benefit. Use of an implicit trust anchor database is NOT
RECOMMENDED when server-side key generation is employed. The use of
an encrypted CMS Server-side Key Generation Response is RECOMMENDED.
Regarding the CSR attributes that the CA may list for inclusion in an
enrollment request, there are no real inherent security issues with
the content being conveyed but an adversary who is able to interpose
herself into the conversation could exclude attributes that a server
may want, include attributes that a server may not want, and render
meaningless other attributes that a server may want.
8. References
8.1. Normative References
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2314] Kaliski, B., "PKCS #10: Certification Request Syntax
Version 1.5", RFC 2314, March 1998.
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[RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP",
RFC 2585, May 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
Classes and Attribute Types Version 2.0", RFC 2985,
November 2000.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
November 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC4108] Housley, R., "Using Cryptographic Message Syntax (CMS) to
Protect Firmware Packages", RFC 4108, August 2005.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210, September 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", RFC 4288, December 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
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Encodings", RFC 4648, October 2006.
[RFC5054] Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
"Using the Secure Remote Password (SRP) Protocol for TLS
Authentication", RFC 5054, November 2007.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, January 2008.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, June 2008.
[RFC5273] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC): Transport Protocols", RFC 5273, June 2008.
[RFC5274] Schaad, J. and M. Myers, "Certificate Management Messages
over CMS (CMC): Compliance Requirements", RFC 5274,
June 2008.
[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, May 2008.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, February 2010.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
April 2010.
[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
for TLS", RFC 5929, July 2010.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
August 2010.
[RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
August 2010.
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[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[RFC6402] Schaad, J., "Certificate Management over CMS (CMC)
Updates", RFC 6402, November 2011.
[SHS] National Institute of Standards and Technology, "Federal
Information Processing Standard Publication 180-4: Secure
Hash Standard (SHS)", March 2012, <http://csrc.nist.gov/
publications/fips/fips180-4/fips-180-4.pdf>.
[X.680] ITU-T Recommendation, "ITU-T Recommendation X.680 Abstract
Syntax Notation One (ASN.1): Specification of basic
notation", November 2008,
<http://www.itu.int/rec/T-REC-X.680-200811-I/en>.
[X.690] ITU-T Recommendation, "ITU-T Recommendation X.690 ASN.1
encoding rules: Specification of Basic Encoding Rules
(BER), Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)", November 2008,
<http://www.itu.int/rec/T-REC-X.690-200811-I/en>.
8.2. Informative References
[IDevID] IEEE Std, "IEEE 802.1AR Secure Device Identifier",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
August 1998.
[RFC2712] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher
Suites to Transport Layer Security (TLS)", RFC 2712,
October 1999.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.
[RFC6403] Zieglar, L., Turner, S., and M. Peck, "Suite B Profile of
Certificate Management over CMS", RFC 6403, November 2011.
[SP-800-57-Part-1]
National Institute of Standards and Technology,
"Recommendation for Key Management - Part 1: General
(Revision 3)", July 2012, <http://csrc.nist.gov/
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publications/nistpubs/800-57/
sp800-57_part1_rev3_general.pdf>.
[X.520] ITU-T Recommendation, "ITU-T Recommendation X.520 The
Directory: Selected attribute types", November 2008,
<http://www.itu.int/rec/T-REC-X.520-200811-I/en>.
Appendix A. Operational Scenario Example Messages
(informative)
This section expands on the Operational Scenario Overviews by
providing detailed examples of the messages at each TLS layer.
A.1. Obtaining CA Certificates
The following is an example of a valid /CACerts exchange.
During the initial TLS handshake the client can ignore the optional
server generated "certificate request" and can instead proceed with
the HTTP GET request:
GET /CACerts HTTP/1.1
User-Agent: curl/7.24.0 (i686-pc-linux-gnu) libcurl/7.24.0 OpenS
SL/0.9.8b zlib/1.2.3 libidn/0.6.5
Host: 127.0.0.1:8085
Accept: */*
In response the server provides the current CA certificates:
HTTP/1.1 200 OK
Status: 200 OK
Content-Type: application/pkcs7-mime
Content-Transfer-Encoding: base64
Content-Length: 4181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knNVdonCC3AtPuBYndnPulF0cQifKEQCZDx00IkPr6+0o60aX4kWRBRiavzaHdqJ
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Rs8Se9pRkVgxoQAxAA==
A.2. Enroll/ReEnroll
The following is an example of a valid /simpleEnroll exchange. The
data messages for /simpleReEnroll are similar.
During this exchange the EST client uses an out-of-band distributed
username/password to authenticate itself to the EST server. This is
the normal HTTP WWW-Authenticate behavior and is included here for
informative purposes. When an existing TLS client certificate is
used the server might skip requesting the HTTP WWW-Authenticate
header, such as during a /simpleReEnroll operation.
During the initial TLS handshake the client can ignore the optional
server generated "certificate request" and can instead proceed with
the HTTP POST request. In response to the initial HTTP POST attempt
the server requests WWW-Authenticate from the client (this might
occur even if the client used a client certificate, as detailed in
the normative text above):
HTTP/1.1 401 Unauthorized
Content-Length: 0
WWW-Authenticate: Digest qop="auth", realm="estrealm",
nonce="1363821319"
In the subsequent HTTP POST the username/password is included, along
with the complete application/pkcs10 content:
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POST /.well-known/est/simpleEnroll HTTP/1.1
Authorization: Digest username="estuser", realm="estrealm", nonc
e="1363821164", uri="/.well-known/est/simpleEnroll", cnonce="MDY
2OTcz", nc=00000002, qop="auth", response="93731653b26bd4693de10
2745c294769"
User-Agent: curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0 OpenS
SL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
Host: 127.0.0.1:8085
Accept: */*
Content-Type: application/pkcs10
Content-Transfer-Encoding: base64
Content-Length: 882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WHSWUBnkq5W4ZKpmxaqFxeZKy/Eyapyqwuk=
The ESTserver uses the username/password to perform authentication/
authorization and responds with the issued certificate:
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HTTP/1.1 200 OK
Status: 200 OK
Content-Type: application/pkcs7-mime
Content-Transfer-Encoding: base64
Content-Length: 1162
MIIDVQYJKoZIhvcNAQcCoIIDRjCCA0ICAQExADALBgkqhkiG9w0BBwGgggMoMIID
JDCCAgygAwIBAgIBGjANBgkqhkiG9w0BAQUFADAbMRkwFwYDVQQDExBlc3RFeGFt
cGxlQ0EgTndOMB4XDTEzMDMyMDIzMTUxOVoXDTE0MDMyMDIzMTUxOVowQTElMCMG
A1UEAxMccmVxIGJ5IGNsaWVudCBpbiBkZW1vIHN0ZXAgMjEYMBYGA1UEBRMPUElE
OldpZGdldCBTTjoyMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4Pw1
JvjhOFL87eMmhIA/bXDORRItgxRZwq6FEQ3cWQvOwiA52hiAfrh/vQZFxIO/d44m
sbSxwbnG61aOEohhQgijUUGn2VxDi5S2xKUZAxnF+UfIP7PpZFg5c6aGO94ZFg6g
T8iI0nRtXvd/T272sTY7n8GTKHfWhzv1nUV11DOzhWG57UC5+rfSqjNhiqtRsHM9
4emXR7rtjtfqY6KFN08x/z5CFKq+EmI5+1GmyUmbzfiCiFejgSULvHqtuMtVuqya
UDWKil0VRbFu0QK3oy5GiIsC4qwoguDRHsW7yO4E5BOLgK9n5PldpJNdEjyEgS7+
dl5MD0nI5j2/pfeFkQIDAQABo00wSzAJBgNVHRMEAjAAMB0GA1UdDgQWBBSxOOKP
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oTANBgkqhkiG9w0BAQUFAAOCAQEAgTNqMhUL1p5TNHiH9McYZuhKF1gW3dLxYpnj
QweZcnSq/cEr1/qRTmMoyb25OySPHzE7Puqh2M2KQb/LqsB/4G1wuQY7eeumOcd+
xwrC8ic+jZaxcNA0+PNXvMdP9JafHZqZVTgF9DoD8a0++7UzUnXG2zSgkN5bvgik
kcAP/D4/4Y1PNFDnolCFg5qGRwCXkPxQU7k458OZI8KHWGXTf5p8Vdo91tVH3LwM
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5zziAdaLFFbfLx6D/HfHrRZe9OLtkPc+1X3LSITE94VEzHfsSqEAMQA=
A.3. Server Key Generation
The following is an example of a valid /serverKeyGen exchange.
During this exchange the EST client authenticates itself using an
existing certificate issued by the CA the EST server provides
services for.
The initial TLS handshake is identical to the enrollment example
handshake. The HTTP POSTed message is:
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POST /.well-known/est/serverKeyGen HTTP/1.1
User-Agent: curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0 OpenS
SL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
Host: 127.0.0.1:8085
Accept: */*
Content-Type: application/pkcs10
Content-Transfer-Encoding: base64
Content-Length: 898
MIICkzCCAXsCAQAwTjEyMDAGA1UEAxMpc2VydmVyS2V5R2VuIHJlcSBieSBjbGll
bnQgaW4gZGVtbyBzdGVwIDUxGDAWBgNVBAUTD1BJRDpXaWRnZXQgU046NTCCASIw
DQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAL3VrdX1IaAcEhQepAtRoA3vhrl/
tVS7ANr8SfCEt6xLNG6YorHoF+jSSYc7bE4gPC1cPkVs8a/tpySnHglD3WdJiCi4
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pf1MdoRpbz62r1+2IljfcVnGIktHy7pY3l8+UlengC3/UybmkKxuaiE8yFBYiImw
iM9GrUSWQCWvrQrk11U9xodCRlLr6Ywe6G7Pb96Oyt2uHW1Qu2sdjR4Kqz8CAwEA
AaAAMA0GCSqGSIb3DQEBBQUAA4IBAQAK6QaV4VgbeGm1tDPu1vX5H7Q6GzPwJZLK
VwyvI3mLXA6vRAfcd20q0rJNddGL9A555L2dEuS4Qo3iqiPBh067M/TUvYU73dSl
kLl0rmqw/Iocvs7LTv4DoCiElmQq2vMIK6IN3vUm96csvDB6WQbd3eqKyPeHlJQf
HAKhpoAn2bls1OLssOmIcWwtZ00GbchIy9XDzJSXKI8EIxZOK1xQ3p5cRO0kNcx9
/MbSg+/wjJ9Xk2DTUux2DOCskCbyc7sizZWF4+LPBtaJOihT5sZyVgEE03hCYAVv
U8z1QKILkt7t7VpWj9GpSHqTWFAyIf4xtfsJwZQWhdsbyT3zZUxS
Because the DecryptKeyIdentifier attribute is not included in the
request the response does not include additional encryption beyond
the TLS session. The EST server response is:
HTTP/1.1 200 OK
Status: 200 OK
Content-Type: multipart/mixed ; boundary=estServerExampleBoundary
Content-Length: 3211
This is the preamble. It is to be ignored, though it
is a handy place for estServer to include an explanatory note
including contact or support information.
--estServerExampleBoundary
Content-Type: application/pkcs8
Content-Transfer-Encoding: base64
MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDUuonyyFBAQzHY
QiHK7pLMc0jDR4LSKtTNQ+Ng9vNMy/PUoJscXKwJzy+D36oLteAKlwIlgAYWMjS6
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XFiEtKSOHzuZq+cTjEHcRUXvFwJLjx1+tcssbLZKwbXHpGnCP5GY2eW5YwMToI23
Gn6FYKoLAgMBAAECggEAHI0czrUL8FQUcI4PswjqMv6WGX+Tk1mkThh6gB0k8n29
MCCOMPRPMtHX8r8mN4QlmcZCx32zU29RnHFUuDJqnP+6OMnZ7lRfJIWS8BLEEw2c
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bwbo0Y80/42kkMH8U7QprbUbrYz/pvEYgcf7a/kqVSZ4+9VjNwbOTgbsYpfxm/Eu
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UL6kvhVapohrlWvGD8xnnmzjE8Pi5gAwdXibfNECgYEAviTObA3hGULCT4YZ33wQ
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MRWeTA9hNk730g8tNnL92K4=
--estServerExampleBoundary
Content-Type: application/pkcs7-mime
Content-Transfer-Encoding: base64
MIIDQAYJKoZIhvcNAQcCoIIDMTCCAy0CAQExADALBgkqhkiG9w0BBwGgggMTMIID
DzCCAfegAwIBAgIBGzANBgkqhkiG9w0BAQUFADAbMRkwFwYDVQQDExBlc3RFeGFt
cGxlQ0EgTndOMB4XDTEzMDMyMDIzMzkyOFoXDTE0MDMyMDIzMzkyOFowLDEqMCgG
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SzAJBgNVHRMEAjAAMB0GA1UdDgQWBBRawN1+4APoSakGRwvD/6i2s+4pDDAfBgNV
HSMEGDAWgBSOayd8CpQKNvBZHkRmdOQvEEJsoTANBgkqhkiG9w0BAQUFAAOCAQEA
YtPAbK4t+sk2ec5svdiNgvK8nsXpyTaHUyX9shuMfTghL/sA6HoSL8y55Cq2pAC/
Ts+vLWvjeJoN8xH7F9lLjx74gFmq/oxkysYCXsc5VcD4Pw5ppQvAL0n52WgX6MZh
GqbGIJykJGvg/FSjqrt4oGo/RQakPnB7dJY/fp9k27DV2nTTkISgPSUzDglM94yj
AbktKu32LN1kv8mt8wBEl1cNUAA2ZpZmzp9fnMgaFNgZBqpbjg07SkgEu8NRcMA5
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f7pEl6EI99JfWRNHIXMXvKEAMQA=
--estServerExampleBoundary--
This is the epilogue. It is also to be ignored.
A.4. CSR Attributes
The following is an example of a valid /CSRAttrs exchange. During
this exchange the EST client authenticates itself using an existing
certificate issued by the CA the EST server provides services for.
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The initial TLS handshake is identical to the enrollment example
handshake. The HTTP GET request:
GET /.well-known/est/CSRAttrs HTTP/1.1
User-Agent: curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0 OpenS
SL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
Host: 127.0.0.1:8085
Accept: */*
In response the server provides suggested attributes that are
appropriate for the authenticated client:
HTTP/1.1 200 OK
Status: 200 OK
Content-Type: application/csrattrs
Content-Transfer-Encoding: base64
Content-Length: 57
MCYGBysGAQEBARYGCSqGSIb3DQEJBwYFK4EEACIGCWCGSAFlAwQCAg==
Authors' Addresses
Max Pritikin (editor)
Cisco Systems, Inc.
510 McCarthy Drive
Milpitas, CA 95035
USA
Email: pritikin@cisco.com
Peter E. Yee (editor)
AKAYLA, Inc.
7150 Moorland Drive
Clarksville, MD 21029
USA
Email: peter@akayla.com
Dan Harkins (editor)
Aruba Networks
1322 Crossman Avenue
Sunnyvale, CA 94089-1113
USA
Email: dharkins@arubanetworks.com
Pritikin, et al. Expires September 30, 2013 [Page 49]