CBOR Encoded Message Syntax (COSE): Headers for carrying and referencing X.509 certificates
draft-schaad-cose-x509-00

Network Working Group                                          J. Schaad
Internet-Draft                                            August Cellars
Intended status: Informational                         November 22, 2016
Expires: May 26, 2017

CBOR Encoded Message Syntax (COSE): Headers for carrying and referencing
                           X.509 certificates
                       draft-schaad-cose-x509-00

Abstract

   This document defines the headers and usage for referring to and
   transporting X.509 certificates in the CBOR Encoded Message (COSE)
   Syntax.

Contributing to this document

   The source for this draft is being maintained in GitHub.  Suggested
   changes should be submitted as pull requests at <https://github.com/
   cose-wg/X509>.  Instructions are on that page as well.  Editorial
   changes can be managed in GitHub, but any substantial issues need to
   be discussed on the COSE mailing list.

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 May 26, 2017.

Copyright Notice

   Copyright (c) 2016 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

Schaad                    Expires May 26, 2017                  [Page 1]
Internet-Draft                 COSE X.509                  November 2016

   (http://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
     1.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   2
   2.  X.509 COSE Headers  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Hash Algorithm Identifiers  . . . . . . . . . . . . . . . . .   5
     3.1.  SHA-2 256-bit Hash  . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  COSE Header Parameter Registry  . . . . . . . . . . . . .   5
     4.2.  COSE Algorithm Registry . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In the process of writing RFCXXXX [I-D.ietf-cose-msg] discussions
   where held on the question of X.509 certificates [RFC5280]  and if
   there were needed.  At the time there were no use cases presented
   that appeared to hve a sufficient set of support to include these
   headers.  Since that time a number of cases where X.509 certificate
   support is necessary have been defined.  This document provides a set
   of headers that will allow applications to transport and refer to
   X.509 certificates in a consistent manner.

1.1.  Requirements 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
   [RFC2119].

   When the words appear in lower case, their natural language meaning
   is used.

Schaad                    Expires May 26, 2017                  [Page 2]
Internet-Draft                 COSE X.509                  November 2016

2.  X.509 COSE Headers

   The use of X.509 certificates allows for an existing trust
   infrastructure to be used with COSE.

   When the header parameters defined in this section are placed in a
   COSE_Signature or COSE_Sign0 object, they identify the key that was
   used for generating signature.

   When the header parameters defined in this section are placed in a
   COSE_recipient structure, they identify the key that was used by the
   sender when used with static-static key agreement algorithms.

   Certificates obtained from any of these methods MUST still be
   validated according to the PKIX rules in [RFC5280].  This includes
   matching against the trust anchors configured for the application.
   This applies certificates of a chain length of one as well as longer
   chains.

   The header parameters defined in this document are:

   x5c:  This header parameter allows for a single or a bag of X.509
      certificates to be carried in the message.

      *  If a single certificate is conveyed, it is placed in a CBOR
         bstr.

      *  If multiple certificates are conveyed, a CBOR array is used
         where:

         +  The first element is a boolean value set to true if the
            certificates are arranged such that a each certificate is
            issued by the next certficate.  In otherwords a chain of
            certificates is presented.  The chain of certificates does
            not need to be complete and normally SHOULD omit the trust
            anchor certificate.  If the first element is set to false,
            then the certificates are not ordered and can include
            certificates that are not needed to create a certificate
            chain from the end-entity certificate.  This allows for a
            certificate with a key exchange algorithm to be carried in a
            signed message.

         +  The second element is the end-entity certificate.  This is
            true regardless of wheither the certificates are ordered or
            not.  This permits the application to identify which
            certificate is the end-entity certificate without a second
            header attribute.

Schaad                    Expires May 26, 2017                  [Page 3]
Internet-Draft                 COSE X.509                  November 2016

         +  Elements three through the last are certificates.

   x5t:  This header parameter provides the ability to identify an X.509
      certificate by a hash value.  The parameter is an array of two
      elements.  The first element is an algorithm identifier which is a
      signed integer, an unsigned integer or a string containing the
      hash algorithm identifier.  The second element is a binary string
      containing the hash value.
      For interoperability, applications which use this header parameter
      MUST support the hash algorithm 'sha256', but can use other hash
      algorithms.

   x5u:  This header parameter provides the ability to identify an X.509
      certificate by a URL.  The referenced resource can be any of the
      following media types:

      *  application/pkix-cert [RFC2585]

      *  application/pkcs7-mime; smime-type="certs-only"
         [I-D.ietf-lamps-rfc5751-bis]

      *  Should we support a PEM type?  I cannot find a registered media
         type for one
      The URL provided MUST provide integrity protection.  For example,
      an HTTP GET request to retrieve a certificate MUST use TLS
      [RFC5246].  If the certificate does not chain to an existing trust
      anchor, the identity of the server MUST be configured as trusted
      to provide new trust anchors.  This will normally be the situation
      when self-signed certificates are used.

   +------+-------+---------------+------------------------------------+
   | name | label | value type    | description                        |
   +------+-------+---------------+------------------------------------+
   | x5t  | TBD1  | COSE_CertHash | Hash of an X.509 certificate       |
   |      |       |               |                                    |
   | x5u  | TBD2  | uri           | URL pointing to an X.509           |
   |      |       |               | certificate                        |
   |      |       |               |                                    |
   | x5c  | TBD3  | COSE_X509     | Collection of X.509 certificates   |
   +------+-------+---------------+------------------------------------+

                        Table 1: X.509 COSE Headers

   COSE_X509 = bstr / [ ordered: bool, certs: +bstr ]
   COSE_CertHash = [ hashAlg: (int / tstr), hashValue: bstr ]

Schaad                    Expires May 26, 2017                  [Page 4]
Internet-Draft                 COSE X.509                  November 2016

3.  Hash Algorithm Identifiers

3.1.  SHA-2 256-bit Hash

   Define an algorithm identifier for SHA-256.

4.  IANA Considerations

4.1.  COSE Header Parameter Registry

   Put in the registrations.

4.2.  COSE Algorithm Registry

   Put in the registrations.

5.  Security Considerations

   There are security considerations:

6.  References

6.1.  Normative References

   [I-D.ietf-cose-msg]
              Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              draft-ietf-cose-msg-23 (work in progress), October 2016.

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

   [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,
              <http://www.rfc-editor.org/info/rfc5280>.

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

6.2.  Informative References

Schaad                    Expires May 26, 2017                  [Page 5]
Internet-Draft                 COSE X.509                  November 2016

   [I-D.greevenbosch-appsawg-cbor-cddl]
              Vigano, C. and H. Birkholz, "CBOR data definition language
              (CDDL): a notational convention to express CBOR data
              structures", draft-greevenbosch-appsawg-cbor-cddl-09 (work
              in progress), September 2016.

   [I-D.ietf-lamps-rfc5751-bis]
              Schaad, J., Ramsdell, B., and S. Turner, "Secure/
              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
              Message Specification", draft-ietf-lamps-rfc5751-bis-02
              (work in progress), October 2016.

   [RFC2585]  Housley, R. and P. Hoffman, "Internet X.509 Public Key
              Infrastructure Operational Protocols: FTP and HTTP",
              RFC 2585, DOI 10.17487/RFC2585, May 1999,
              <http://www.rfc-editor.org/info/rfc2585>.

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

Author's Address

   Jim Schaad
   August Cellars

   Email: ietf@augustcellars.com

Schaad                    Expires May 26, 2017                  [Page 6]