Handling Large Certificates and Long Certificate Chains in TLS-based EAP Methods
draft-ietf-emu-eaptlscert-08

Document Type Active Internet-Draft (emu WG)
Authors Mohit Sethi  , John Preuß Mattsson  , Sean Turner 
Last updated 2020-11-20
Replaces draft-ms-emu-eaptlscert
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Network Working Group                                           M. Sethi
Internet-Draft                                               J. Mattsson
Intended status: Informational                                  Ericsson
Expires: May 24, 2021                                          S. Turner
                                                                   sn3rd
                                                       November 20, 2020

        Handling Large Certificates and Long Certificate Chains
                        in TLS-based EAP Methods
                      draft-ietf-emu-eaptlscert-08

Abstract

   The Extensible Authentication Protocol (EAP), defined in RFC3748,
   provides a standard mechanism for support of multiple authentication
   methods.  EAP-Transport Layer Security (EAP-TLS) and other TLS-based
   EAP methods are widely deployed and used for network access
   authentication.  Large certificates and long certificate chains
   combined with authenticators that drop an EAP session after only 40 -
   50 round-trips is a major deployment problem.  This document looks at
   this problem in detail and describes the potential solutions
   available.

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 https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on May 24, 2021.

Copyright Notice

   Copyright (c) 2020 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

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Experience with Deployments . . . . . . . . . . . . . . . . .   4
   4.  Handling of Large Certificates and Long Certificate Chains  .   5
     4.1.  Updating Certificates and Certificate Chains  . . . . . .   5
       4.1.1.  Guidelines for Certificates . . . . . . . . . . . . .   6
       4.1.2.  Pre-distributing and Omitting CA certificates . . . .   7
       4.1.3.  Using Fewer Intermediate Certificates . . . . . . . .   7
     4.2.  Updating TLS and EAP-TLS Code . . . . . . . . . . . . . .   7
       4.2.1.  URLs for Client Certificates  . . . . . . . . . . . .   7
       4.2.2.  Caching Certificates  . . . . . . . . . . . . . . . .   8
       4.2.3.  Compressing Certificates  . . . . . . . . . . . . . .   8
       4.2.4.  Compact TLS 1.3 . . . . . . . . . . . . . . . . . . .   9
       4.2.5.  Suppressing Intermediate Certificates . . . . . . . .   9
       4.2.6.  Raw Public Keys . . . . . . . . . . . . . . . . . . .   9
       4.2.7.  New Certificate Types and Compression Algorithms  . .  10
     4.3.  Updating Authenticators . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The Extensible Authentication Protocol (EAP), defined in [RFC3748],
   provides a standard mechanism for support of multiple authentication
   methods.  EAP-Transport Layer Security (EAP-TLS) [RFC5216]
   [I-D.ietf-emu-eap-tls13] relies on TLS [RFC8446] to provide strong
   mutual authentication with certificates [RFC5280] and is widely
   deployed and often used for network access authentication.  There are
   also many other TLS-based EAP methods, such as Flexible
   Authentication via Secure Tunneling (EAP-FAST) [RFC4851], Tunneled
   Transport Layer Security (EAP-TTLS) [RFC5281], Tunnel Extensible
   Authentication Protocol (EAP-TEAP) [RFC7170], and possibly many
   vendor-specific EAP methods.

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   Certificates in EAP deployments can be relatively large, and the
   certificate chains can be long.  Unlike the use of TLS on the web,
   where typically only the TLS server is authenticated; EAP-TLS
   deployments typically authenticate both the EAP peer and the EAP
   server.  Also, from deployment experience, EAP peers typically have
   longer certificate chains than servers.  This is because EAP peers
   often follow organizational hierarchies and tend to have many
   intermediate certificates.  Thus, EAP-TLS authentication usually
   involves exchange of significantly more octets than when TLS is used
   as part of HTTPS.

   Section 3.1 of [RFC3748] states that EAP implementations can assume a
   Maximum Transmission Unit (MTU) of at least 1020 octets from lower
   layers.  The EAP fragment size in typical deployments is just 1020 -
   1500 octets (since the maximum Ethernet frame size is ~ 1500 bytes).
   Thus, EAP-TLS authentication needs to be fragmented into many smaller
   packets for transportation over the lower layers.  Such fragmentation
   not only can negatively affect the latency, but also results in other
   challenges.  For example, some EAP authenticator (access point)
   implementations will drop an EAP session if it has not finished after
   40 - 50 round-trips.  This is a major problem and means that in many
   situations, the EAP peer cannot perform network access authentication
   even though both the sides have valid credentials for successful
   authentication and key derivation.

   Not all EAP deployments are constrained by the MTU of the lower
   layer.  For example, some implementations support EAP over Ethernet
   "Jumbo" frames that can easily allow very large EAP packets.  Larger
   packets will naturally help lower the number of round trips required
   for successful EAP-TLS authentication.  However, deployment
   experience has shown that these jumbo frames are not always
   implemented correctly.  Additionally, EAP fragment size is also
   restricted by protocols such as RADIUS [RFC2865] which are
   responsible for transporting EAP messages between an authenticator
   and an EAP server.  RADIUS can generally transport only about 4000
   octets of EAP in a single message (the maximum length of RADIUS
   packet is restricted to 4096 octets in [RFC2865]).

   This document looks at related work and potential tools available for
   overcoming the deployment challenges induced by large certificates
   and long certificate chains.  It then discusses the solutions
   available to overcome these challenges.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP

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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Readers are expected to be familiar with the terms and concepts used
   in EAP [RFC3748], EAP-TLS [RFC5216], and TLS [RFC8446].  In
   particular, this document frequently uses the following terms as they
   have been defined in [RFC5216]:

   Authenticator  The entity initiating EAP authentication.  Typically
         implemented as part of a network switch or a wireless access
         point.

   EAP peer  The entity that responds to the authenticator.  In
         [IEEE-802.1X], this entity is known as the supplicant.  In EAP-
         TLS, the EAP peer implements the TLS client role.

   EAP server  The entity that terminates the EAP authentication method
         with the peer.  In the case where no backend authentication
         server is used, the EAP server is part of the authenticator.
         In the case where the authenticator operates in pass-through
         mode, the EAP server is located on the backend authentication
         server.  In EAP-TLS, the EAP server implements the TLS server
         role.

   The document additionally uses the terms "trust anchor" and
   "certification path" defined in [RFC5280].

3.  Experience with Deployments

   As stated earlier, the EAP fragment size in typical deployments is
   just 1020 - 1500 octets.  A certificate can, however, be large for a
   number of reasons:

   o  It can have a long Subject Alternative Name field.

   o  It can have long Public Key and Signature fields.

   o  It can contain multiple object identifiers (OID) that indicate the
      permitted uses of the certificate as noted in Section 5.3 of
      [RFC5216].  Most implementations verify the presence of these OIDs
      for successful authentication.

   o  It can contain multiple organization fields to reflect the
      multiple group memberships of a user (in a client certificate).

   A certificate chain (called a certification path in [RFC5280]) in
   EAP-TLS can commonly have 2 - 6 intermediate certificates between the
   end-entity certificate and the trust anchor.

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   The size of certificates (and certificate chains) may also increase
   many-fold in the future with the introduction of quantum-safe
   cryptography.  For example, lattice-based cryptography would have
   public keys of approximately 1000 bytes and signatures of
   approximately 2000 bytes.

   Many access point implementations drop EAP sessions that do not
   complete within 40 - 50 round-trips.  This means that if the chain is
   larger than ~ 60 kbytes, EAP-TLS authentication cannot complete
   successfully in most deployments.

4.  Handling of Large Certificates and Long Certificate Chains

   This section discusses some possible alternatives for overcoming the
   challenge of large certificates and long certificate chains in EAP-
   TLS authentication.  Section 4.1 considers recommendations that
   require an update of the certificates or certificate chains used for
   EAP-TLS authentication without requiring changes to the existing EAP-
   TLS code base.  It also provides some guidelines that should be
   followed when issuing certificates for use with EAP-TLS.  Section 4.2
   considers recommendations that rely on updates to the EAP-TLS
   implementations and can be deployed with existing certificates.
   Finally, Section 4.3 briefly discusses what could be done to update
   or reconfigure authenticators when it is infeasible to replace
   deployed components giving a solution which can be deployed without
   changes to existing certificates or code.

4.1.  Updating Certificates and Certificate Chains

   Many IETF protocols now use elliptic curve cryptography (ECC)
   [RFC6090] for the underlying cryptographic operations.  The use of
   ECC can reduce the size of certificates and signatures.  For example,
   at a 128-bit security level, the size of a public key with
   traditional RSA is about 384 bytes, while the size of a public key
   with ECC is only 32-64 bytes.  Similarly, the size of a digital
   signature with traditional RSA is 384 bytes, while the size is only
   64 bytes with elliptic curve digital signature algorithm (ECDSA) and
   Edwards-curve digital signature algorithm (EdDSA) [RFC8032].  Using
   certificates that use ECC can reduce the number of messages in EAP-
   TLS authentication, which can alleviate the problem of authenticators
   dropping an EAP session because of too many round-trips.  In the
   absence of a standard application profile specifying otherwise, TLS
   1.3 [RFC8446] requires implementations to support ECC.  New cipher
   suites that use ECC are also specified for TLS 1.2 [RFC8422].  Using
   ECC-based cipher suites with existing code can significantly reduce
   the number of messages in a single EAP session.

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4.1.1.  Guidelines for Certificates

   The general guideline of keeping the certificate size small by not
   populating fields with excessive information can help avert the
   problems of failed EAP-TLS authentication.  More specific
   recommendations for certificates used with EAP-TLS are as follows:

   o  Object Identifier (OID) is an ASN.1 data type that defines unique
      identifiers for objects.  The OID's ASN.1 value, which is a string
      of integers, is then used to name objects to which they relate.
      The Distinguished Encoding Rules (DER) specify that the first two
      integers always occupy one octet and subsequent integers are base
      128-encoded in the fewest possible octets.  OIDs are used lavishly
      in X.509 certificates [RFC5280] and while not all can be avoided,
      e.g., OIDs for extensions or algorithms and their associate
      parameters, some are well within the certificate issuer's control:

      *  Each naming attribute in a DN (Directory Name) has one.  DNs
         are used in the issuer and subject fields as well as numerous
         extensions.  A shallower naming will be smaller, e.g., C=FI,
         O=Example, SN=B0A123499EFC as against C=FI, O=Example,
         OU=Division 1, SOPN=Southern Finland, CN=Coolest IoT Gadget
         Ever, SN=B0A123499EFC.

      *  Every certificate policy (and qualifier) and any mappings to
         another policy uses identifiers.  Consider carefully what
         policies apply.

   o  DirectoryString and GeneralName types are used extensively to name
      things, e.g., the DN naming attribute O= (the organizational
      naming attribute) DirectoryString includes "Example" for the
      Example organization and uniformResourceIdentifier can be used to
      indicate the location of the CRL, e.g., "http://crl.example.com/
      sfig2s1-128.crl", in the CRL Distribution Point extension.  For
      these particular examples, each character is a byte.  For some
      non-ASCII character strings in the DN, characters can be multi-
      byte.  Obviously, the names need to be unique, but there is more
      than one way to accomplish this without long strings.  This is
      especially true if the names are not meant to be meaningful to
      users.

   o  Extensions are necessary to comply with [RFC5280], but the vast
      majority are optional.  Include only those that are necessary to
      operate.

   o  As stated earlier, certificate chains of the EAP peer often follow
      organizational hierarchies.  In such cases, information in
      intermediate certificates (such as postal addresses) do not

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      provide any additional value and they can be shortened (for
      example: only including the department name instead of the full
      postal address).

4.1.2.  Pre-distributing and Omitting CA certificates

   The TLS Certificate message conveys the sending endpoint's
   certificate chain.  TLS allows endpoints to reduce the size of the
   Certificate message by omitting certificates that the other endpoint
   is known to possess.  When using TLS 1.3, all certificates that
   specify a trust anchor known by the other endpoint may be omitted
   (see Section 4.4.2 of [RFC8446]).  When using TLS 1.2 or earlier,
   only the self-signed certificate that specifies the root certificate
   authority may be omitted (see Section 7.4.2 of [RFC5246] Therefore,
   updating TLS implementations to version 1.3 can help to significantly
   reduce the number of messages exchanged for EAP-TLS authentication.
   The omitted certificates need to be pre-distributed independently of
   TLS and the TLS implementations need to be configured to omit these
   pre-distributed certificates.

4.1.3.  Using Fewer Intermediate Certificates

   The EAP peer certificate chain does not have to mirror the
   organizational hierarchy.  For successful EAP-TLS authentication,
   certificate chains SHOULD NOT contain more than 4 intermediate
   certificates.

   Administrators responsible for deployments using TLS-based EAP
   methods can examine the certificate chains and make rough
   calculations about the number of round trips required for successful
   authentication.  For example, dividing the total size of all the
   certificates in the peer and server certificate chain (in bytes) by
   1020 bytes will indicate the minimum number of round trips required.
   If this number exceeds 50, then, administrators can expect failures
   with many common authenticator implementations.

4.2.  Updating TLS and EAP-TLS Code

   This section discusses how the fragmentation problem can be avoided
   by updating the underlying TLS or EAP-TLS implementation.  Note that
   in some cases the new feature may already be implemented in the
   underlying library and simply needs to be taken into use.

4.2.1.  URLs for Client Certificates

   [RFC6066] defines the "client_certificate_url" extension which allows
   TLS clients to send a sequence of Uniform Resource Locators (URLs)
   instead of the client certificate.  URLs can refer to a single

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   certificate or a certificate chain.  Using this extension can curtail
   the amount of fragmentation in EAP deployments thereby allowing EAP
   sessions to successfully complete.

4.2.2.  Caching Certificates

   The TLS Cached Information Extension [RFC7924] specifies an extension
   where a server can exclude transmission of certificate information
   cached in an earlier TLS handshake.  The client and the server would
   first execute the full TLS handshake.  The client would then cache
   the certificate provided by the server.  When the TLS client later
   connects to the same TLS server without using session resumption, it
   can attach the "cached_info" extension to the ClientHello message.
   This would allow the client to indicate that it has cached the
   certificate.  The client would also include a fingerprint of the
   server certificate chain.  If the server's certificate has not
   changed, then the server does not need to send its certificate and
   the corresponding certificate chain again.  In case information has
   changed, which can be seen from the fingerprint provided by the
   client, the certificate payload is transmitted to the client to allow
   the client to update the cache.  The extension however necessitates a
   successful full handshake before any caching.  This extension can be
   useful when, for example, a successful authentication between an EAP
   peer and EAP server has occurred in the home network.  If
   authenticators in a roaming network are stricter at dropping long EAP
   sessions, an EAP peer can use the Cached Information Extension to
   reduce the total number of messages.

   However, if all authenticators drop the EAP session for a given EAP
   peer and EAP server combination, a successful full handshake is not
   possible.  An option in such a scenario would be to cache validated
   certificate chains even if the EAP-TLS exchange fails, but such
   caching is currently not specified in [RFC7924].

4.2.3.  Compressing Certificates

   The TLS working group is also working on an extension for TLS 1.3
   [I-D.ietf-tls-certificate-compression] that allows compression of
   certificates and certificate chains during full handshakes.  The
   client can indicate support for compressed server certificates by
   including this extension in the ClientHello message.  Similarly, the
   server can indicate support for compression of client certificates by
   including this extension in the CertificateRequest message.  While
   such an extension can alleviate the problem of excessive
   fragmentation in EAP-TLS, it can only be used with TLS version 1.3
   and higher.  Deployments that rely on older versions of TLS cannot
   benefit from this extension.

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4.2.4.  Compact TLS 1.3

   [I-D.ietf-tls-ctls] defines a "compact" version of TLS 1.3 and
   reduces the message size of the protocol by removing obsolete
   material and using more efficient encoding.  It also defines a
   compression profile with which either side can define a dictionary of
   "known certificates".  Thus, cTLS could provide another mechanism for
   EAP-TLS deployments to reduce the size of messages and avoid
   excessive fragmentation.

4.2.5.  Suppressing Intermediate Certificates

   For a client that has all intermediate certificates in the
   certificate chain, having the server send intermediates in the TLS
   handshake increases the size of the handshake unnecessarily.
   [I-D.thomson-tls-sic] proposes an extension for TLS 1.3 that allows a
   TLS client that has access to the complete set of published
   intermediate certificates to inform servers of this fact so that the
   server can avoid sending intermediates, reducing the size of the TLS
   handshake.  The mechanism is intended to be complementary with
   certificate compression.

   The Authority Information Access (AIA) extension specified in
   [RFC5280] can be used with end-entity and CA certificates to access
   information about the issuer of the certificate in which the
   extension appears.  For example, it can be used to provide the
   address of the OCSP responder from where revocation status of the
   certificate (in which the extension appears) can be checked.  It can
   also be used to obtain the issuer certificate.  Thus, the AIA
   extension can reduce the size of the certificate chain by only
   including a pointer to the issuer certificate instead of including
   the entire issuer certificate.  However, it requires the side
   receiving the certificate containing the extension to have network
   connectivity (unless the information is already cached locally).
   Naturally, such indirection cannot be used for the server certificate
   (since EAP peers in most deployments do not have network connectivity
   before authentication and typically do not maintain an up-to-date
   local cache of issuer certificates).

4.2.6.  Raw Public Keys

   [RFC7250] defines a new certificate type and TLS extensions to enable
   the use of raw public keys for authentication.  Raw public keys use
   only a subset of information found in typical certificates and are
   therefore much smaller in size.  However, raw public keys require an
   out-of-band mechanism to bind the public key with the entity
   presenting the key.  Using raw public keys will obviously avoid the
   fragmentation problems resulting from large certificates and long

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   certificate chains.  Deployments can consider their use as long as an
   appropriate out-of-band mechanism for binding public keys with
   identifiers is in place.  Naturally, deployments will also need to
   consider the challenges of revocation and key rotation with the use
   of raw public keys.

4.2.7.  New Certificate Types and Compression Algorithms

   There is ongoing work to specify new certificate types which are
   smaller than traditional X.509 certificates.  For example,
   [I-D.mattsson-cose-cbor-cert-compress] defines a Concise Binary
   Object Representation (CBOR) [RFC7049] encoding of X.509
   Certificates.  The CBOR encoding can be used to compress existing
   X.509 certificate or for natively signed CBOR certificates.
   [I-D.tschofenig-tls-cwt] registers a new TLS Certificate type which
   would enable TLS implementations to use CBOR Web Tokens (CWTs)
   [RFC8392] as certificates.  While these are early initiatives, future
   EAP-TLS deployments can consider the use of these new certificate
   types and compression algorithms to avoid large message sizes.

4.3.  Updating Authenticators

   There are several legitimate reasons that authenticators may want to
   limit the number of round-trips/packets/octets that can be sent.  The
   main reason has been to work around issues where the EAP peer and EAP
   server end up in an infinite loop ACKing their messages.  Another
   reason is that unlimited communication from an unauthenticated device
   using EAP could provide a channel for inappropriate bulk data
   transfer.  A third reason is to prevent denial-of-service attacks.

   Updating the millions of already deployed access points and switches
   is in many cases not realistic.  Vendors may be out of business or no
   longer supporting the products and administrators may have lost the
   login information to the devices.  For practical purposes the EAP
   infrastructure is ossified for the time being.

   Vendors making new authenticators should consider increasing the
   number of round-trips allowed to 100 before denying the EAP
   authentication to complete.  Based on the size of the certificates
   and certificate chains currently deployed, such an increase would
   likely ensure that peers and servers can complete EAP-TLS
   authentication.  At the same time, administrators responsible for EAP
   deployments should ensure that this 100 roundtrip limit is not
   exceeded in practice.

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5.  IANA Considerations

   This document includes no request to IANA.

6.  Security Considerations

   Updating implementations to TLS version 1.3 allows omitting all
   certificates with a trust anchor known by the other endpoint.  TLS
   1.3 additionally provides improved security, privacy, and reduced
   latency for EAP-TLS [I-D.ietf-emu-eap-tls13].

   Security considerations when compressing certificates are specified
   in [I-D.ietf-tls-certificate-compression].

   Specific security considerations of the referenced documents apply
   when they are taken into use.

7.  References

7.1.  Normative References

   [I-D.ietf-emu-eap-tls13]
              Mattsson, J. and M. Sethi, "Using EAP-TLS with TLS 1.3",
              draft-ietf-emu-eap-tls13-12 (work in progress), November
              2020.

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

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
              <https://www.rfc-editor.org/info/rfc3748>.

   [RFC4851]  Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou, "The
              Flexible Authentication via Secure Tunneling Extensible
              Authentication Protocol Method (EAP-FAST)", RFC 4851,
              DOI 10.17487/RFC4851, May 2007,
              <https://www.rfc-editor.org/info/rfc4851>.

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
              March 2008, <https://www.rfc-editor.org/info/rfc5216>.

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

   [RFC5281]  Funk, P. and S. Blake-Wilson, "Extensible Authentication
              Protocol Tunneled Transport Layer Security Authenticated
              Protocol Version 0 (EAP-TTLSv0)", RFC 5281,
              DOI 10.17487/RFC5281, August 2008,
              <https://www.rfc-editor.org/info/rfc5281>.

   [RFC7170]  Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
              "Tunnel Extensible Authentication Protocol (TEAP) Version
              1", RFC 7170, DOI 10.17487/RFC7170, May 2014,
              <https://www.rfc-editor.org/info/rfc7170>.

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

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

7.2.  Informative References

   [I-D.ietf-tls-certificate-compression]
              Ghedini, A. and V. Vasiliev, "TLS Certificate
              Compression", draft-ietf-tls-certificate-compression-10
              (work in progress), January 2020.

   [I-D.ietf-tls-ctls]
              Rescorla, E., Barnes, R., and H. Tschofenig, "Compact TLS
              1.3", draft-ietf-tls-ctls-01 (work in progress), November
              2020.

   [I-D.mattsson-cose-cbor-cert-compress]
              Raza, S., Hoglund, J., Selander, G., Mattsson, J., and M.
              Furuhed, "CBOR Encoding of X.509 Certificates (CBOR
              Certificates)", draft-mattsson-cose-cbor-cert-compress-03
              (work in progress), November 2020.

   [I-D.thomson-tls-sic]
              Thomson, M., "Suppressing Intermediate Certificates in
              TLS", draft-thomson-tls-sic-00 (work in progress), March
              2019.

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   [I-D.tschofenig-tls-cwt]
              Tschofenig, H. and M. Brossard, "Using CBOR Web Tokens
              (CWTs) in Transport Layer Security (TLS) and Datagram
              Transport Layer Security (DTLS)", draft-tschofenig-tls-
              cwt-02 (work in progress), July 2020.

   [IEEE-802.1X]
              Institute of Electrical and Electronics Engineers, "IEEE
              Standard for Local and metropolitan area networks -- Port-
              Based Network Access Control", IEEE Standard 802.1X-2010 ,
              February 2010.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,
              <https://www.rfc-editor.org/info/rfc2865>.

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

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <https://www.rfc-editor.org/info/rfc6066>.

   [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
              Curve Cryptography Algorithms", RFC 6090,
              DOI 10.17487/RFC6090, February 2011,
              <https://www.rfc-editor.org/info/rfc6090>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <https://www.rfc-editor.org/info/rfc7250>.

   [RFC7924]  Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", RFC 7924,
              DOI 10.17487/RFC7924, July 2016,
              <https://www.rfc-editor.org/info/rfc7924>.

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   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/info/rfc8392>.

   [RFC8422]  Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
              Curve Cryptography (ECC) Cipher Suites for Transport Layer
              Security (TLS) Versions 1.2 and Earlier", RFC 8422,
              DOI 10.17487/RFC8422, August 2018,
              <https://www.rfc-editor.org/info/rfc8422>.

Acknowledgements

   This draft is a result of several useful discussions with Alan DeKok,
   Bernard Aboba, Jari Arkko, Jouni Malinen, Darshak Thakore, and Hannes
   Tschofening.

Authors' Addresses

   Mohit Sethi
   Ericsson
   Jorvas  02420
   Finland

   Email: mohit@piuha.net

   John Mattsson
   Ericsson
   Kista
   Sweden

   Email: john.mattsson@ericsson.com

   Sean Turner
   sn3rd

   Email: sean@sn3rd.com

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