[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-schaad-cose-x509) 00 01

Network Working Group                                          J. Schaad
Internet-Draft                                            August Cellars
Intended status: Informational                            March 11, 2019
Expires: September 12, 2019


  CBOR Object Signing and Encryption (COSE): Headers for carrying and
                     referencing X.509 certificates
                        draft-ietf-cose-x509-01

Abstract

   The CBOR Signing And Encrypted Message (COSE) structure syntax uses
   the COSE Key structure for placing keys in a message.  This document
   extends the way that keys can be identified and transported by
   providing attributes that refer to or contain X.509 certificates.

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 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 September 12, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





Schaad                 Expires September 12, 2019               [Page 1]


Internet-Draft                 COSE X.509                     March 2019


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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
     1.2.  Open Questions  . . . . . . . . . . . . . . . . . . . . .   3
   2.  X.509 COSE Headers  . . . . . . . . . . . . . . . . . . . . .   3
   3.  X.509 certificates and static-static ECDH . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  COSE Header Parameter Registry  . . . . . . . . . . . . .   7
     4.2.  COSE Header Algorithm Parameter Registry  . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   In the process of writing [RFC8152] discussions where held on the
   question of X.509 certificates [RFC5280] and if there was a needed to
   provide for them.  At the time there were no use cases presented that
   appeared to have a sufficient need for these attributes.  Since that
   time a number of cases where X.509 certificate support is necessary
   have been defined.  This document provides a set of attributes that
   will allow applications to transport and refer to X.509 certificates
   in a consistent manner.

   Some of the constrained device situations are being used where an
   X.509 PKI is already installed.  One of these situations is the 6tish
   environment for enrollment of devices where the certificates are
   installed at the factory.  The [I-D.selander-ace-cose-ecdhe] draft
   was also written with the idea that long term certificates could be
   used to provide for authentication of devices and uses them to
   establish session keys.  A final scenario is the use of COSE as a
   messaging application where long term existence of keys can be used
   along with a central authentication authority.  The use of
   certificates in this scenario allows for key management to be used
   which is well understood.



Schaad                 Expires September 12, 2019               [Page 2]


Internet-Draft                 COSE X.509                     March 2019


   Example COSE messages for the various headers defined below can be
   found at https://github.com/cose-wg/Examples.  THIS IS NOT YET DONE
   BUT SHOULD BE COMING NOT LONG AFTER THE F2F MEETING.

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

1.2.  Open Questions

      Should we define an extended key usage?

      Are there any special certificate valiation text to be added?

      Specific security considerations issues.

      Revocation info?

      Ties to a COSE_Key?

2.  X.509 COSE Headers

   The use of X.509 certificates allows for an existing trust
   infrastructure to be used with COSE.  This includes the full suite of
   enrollment protocols, trust anchors, trust chaining and revocation
   checking that have been defined over time by the IETF and other
   organizations.  The key structures that have been defined in COSE
   currently do not support all of these properties although some may be
   found in COSE Web Tokens (CWT) [RFC8392].

   It is not necessarily expected that constrained devices will fully
   support the evaluation and processing of X.509 certificates, it is
   perfectly reasonable for a certificate to be assigned to a device
   which it can then provide to a relying party along with a signature
   or encrypted message, the relying party not being a constrained
   device.

   Certificates obtained from any of these methods MUST still be
   validated.  This validation can be done via the PKIX rules in
   [RFC5280] or by using a different trust structure, such as a trusted
   certificate distributer for self-signed certificates.  The PKIX
   validation includes matching against the trust anchors configured for
   the application.  These rules apply to certificates of a chain length




Schaad                 Expires September 12, 2019               [Page 3]


Internet-Draft                 COSE X.509                     March 2019


   of one as well as longer chains.  If the application cannot establish
   a trust in the certificate, then it cannot be used.

   The header attributes defined in this document are:

   x5bag:  This header attributes contains a bag of X.509 certificates.
      The set of certificates in this header are unordered and may
      contain self-signed certificates.  The certificate bag can contain
      certificates which are completely extraneous to the message.  (An
      example of this would be to carry a certificate with a key
      agreement key usage in a signed message.)  As the certificates are
      unordered, the party evaluating the signature will need to do the
      necessary path building.  Certificates needed for any particular
      chain to be built may be absent from the bag.

      As this header element does not provide any trust, the header
      attribute can be in either a protected or unprotected header
      attribute.

      This header attribute 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 of bstrs is
         used.  Each certificate being in it's own slot.

   x5chain:  This header attribute contains an ordered array of X.509
      certificates.  The certificates are to be ordered starting with
      the certificate containing the end-entity key followed by the
      certificate which signed it and so on.  There is no requirement
      for the entire chain to be present in the element if there is
      reason to believe that the relying party will already have it.
      This means that the relying party is still required to do path
      building, but that a candidate path is proposed in this attribute.

      As this header element does not provide any trust, the header
      attribute can be in either a protected or unprotected header
      attribute.

      This header attribute allows for a single or a chain of X.509
      certificates to be carried in the message.

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





Schaad                 Expires September 12, 2019               [Page 4]


Internet-Draft                 COSE X.509                     March 2019


      *  If multiple certificates are conveyed, a CBOR array of bstrs is
         used.  Each certificate being in it's own slot.

   x5t:  This header attribute provides the ability to identify an X.509
      certificate by a hash value.  The attribute is an array of two
      elements.  The first element is an algorithm identifier which is
      an integer or a string containing the hash algorithm identifier.
      The second element is a binary string containing the hash value.

      As this header element does not provide any trust, the header
      attribute can be in either a protected or unprotected header
      attribute.
      For interoperability, applications which use this header attribute
      MUST support the hash algorithm 'sha256', but can use other hash
      algorithms.

   x5u:  This header attribute 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]

      *  application/pem-certificate-chain [I-D.ietf-acme-acme]

      As this header attribute implies a trust relationship, the
      attribute MUST be in the protected attributes.
      The URL provided MUST provide integrity protection and server
      authentication.  For example, an HTTP or CoAP GET request to
      retrieve a certificate MUST use TLS [RFC8446] or DTLS
      [I-D.ietf-tls-dtls13].  If the certificate does not chain to an
      existing trust anchor, the certificate MUST NOT be trusted unless
      the server is configured as trusted to provide new trust anchors.
      This will normally be the situation when self-signed certificates
      are used.

   The header attributes are used in the following locations:

   o  COSE_Signature and COSE_Sign0 objects, in these objects they
      identify the key that was used for generating signature.

   o  COSE_recipient objects, in this location they may be used to
      identify the certificate for the recipient of the message.






Schaad                 Expires September 12, 2019               [Page 5]


Internet-Draft                 COSE X.509                     March 2019


   +---------+-------+---------------+---------------------------------+
   | Name    | Value | value type    | description                     |
   +---------+-------+---------------+---------------------------------+
   | x5bag   | TBD4  | COSE_X509     | An unordered bag of X.509       |
   |         |       |               | certificates                    |
   |         |       |               |                                 |
   | x5chain | TBD3  | COSE_X509     | An ordered chain of X.509       |
   |         |       |               | certificates                    |
   |         |       |               |                                 |
   | x5t     | TBD1  | COSE_CertHash | Hash of an X.509 certificate    |
   |         |       |               |                                 |
   | x5u     | TBD2  | uri           | URL pointing to an X.509        |
   |         |       |               | certificate                     |
   +---------+-------+---------------+---------------------------------+

                        Table 1: X.509 COSE Headers

   Below is an equivalent CDDL [I-D.ietf-cbor-cddl] description of the
   text above.

   COSE_X509 = bstr / [ 2*certs: bstr ]
   COSE_CertHash = [ hashAlg: (int / tstr), hashValue: bstr ]

3.  X.509 certificates and static-static ECDH

   The header attributes defined in the previous section are used to
   identify the recipient certificates for the ECDH key agreement
   algorithms.  In this section we define the algorithm specific
   parameters that are used for identifying or transporting the senders
   key for static-static key agreement algorithms.

   These attributes are defined analogously to those in the previous
   section.  There is no definition for the certificate bag as the same
   attribute would be used for both the sender and recipient
   certificates.

   x5chain-sender:  This header attribute contains the chain of
      certificates starting with the sender's key exchange certificate.
      The structure is the same as 'x5bag'.

   x5t-sender:  This header attribute contains the hash value for the
      sender's key exchange certificate.  The structure is the same as
      'x5t'.

   x5u-sender:  This header attribute contains a URL for the sender's
      key exchange certificate.  The structure and processing are the
      same as 'x5u'.




Schaad                 Expires September 12, 2019               [Page 6]


Internet-Draft                 COSE X.509                     March 2019


   +--------------+------+--------------+-----------------+------------+
   | Name         | Valu | Type         | Algorithm       | Descriptio |
   |              | e    |              |                 | n          |
   +--------------+------+--------------+-----------------+------------+
   | x5t-sender   | TBD  | COSE_CertHas | ECDH-           | Thumbprint |
   |              |      | h            | SS+HKDF-256,    | for the    |
   |              |      |              | ECDH-           | senders    |
   |              |      |              | SS+HKDF-512,    | X.509 cert |
   |              |      |              | ECDH-SS+A128KW, | ificate    |
   |              |      |              | ECDH-           |            |
   |              |      |              | SS+AES192KW,    |            |
   |              |      |              | ECDH-           |            |
   |              |      |              | SS+AES256KW     |            |
   |              |      |              |                 |            |
   | x5u-sender   | TBD  | uri          | ECDH-           | URL for    |
   |              |      |              | SS+HKDF-256,    | the        |
   |              |      |              | ECDH-           | senders    |
   |              |      |              | SS+HKDF-512,    | X.509 cert |
   |              |      |              | ECDH-SS+A128KW, | ificate    |
   |              |      |              | ECDH-           |            |
   |              |      |              | SS+AES192KW,    |            |
   |              |      |              | ECDH-           |            |
   |              |      |              | SS+AES256KW     |            |
   |              |      |              |                 |            |
   | x5chain-     | TBD  | COSE_X509    | ECDH-           | static key |
   | sender       |      |              | SS+HKDF-256,    | X.509 cert |
   |              |      |              | ECDH-           | ificate    |
   |              |      |              | SS+HKDF-512,    | chain      |
   |              |      |              | ECDH-SS+A128KW, |            |
   |              |      |              | ECDH-           |            |
   |              |      |              | SS+AES192KW,    |            |
   |              |      |              | ECDH-           |            |
   |              |      |              | SS+AES256KW     |            |
   +--------------+------+--------------+-----------------+------------+

                   Table 2: Static ECDH Algorithm Values

4.  IANA Considerations

4.1.  COSE Header Parameter Registry

   IANA is requested to register the new COSE Header items in Table 1 in
   the "COSE Header Parameters" registry.








Schaad                 Expires September 12, 2019               [Page 7]


Internet-Draft                 COSE X.509                     March 2019


4.2.  COSE Header Algorithm Parameter Registry

   IANA is requested to register the new COSE Header items in Table 2 in
   the "COSE Header Algorithm Parameters" registry.

5.  Security Considerations

   There are security considerations:

      Self-signed certificates and Trust Anchors

6.  References

6.1.  Normative References

   [I-D.schaad-cose-rfc8152bis-struct]
              Schaad, J., "CBOR Object Signing and Encryption (COSE) -
              Structures and Process", draft-schaad-cose-rfc8152bis-
              struct-01 (work in progress), December 2018.

   [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>.

   [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>.

   [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>.

6.2.  Informative References

   [I-D.ietf-acme-acme]
              Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
              Kasten, "Automatic Certificate Management Environment
              (ACME)", draft-ietf-acme-acme-18 (work in progress),
              December 2018.

   [I-D.ietf-cbor-cddl]
              Birkholz, H., Vigano, C., and C. Bormann, "Concise data
              definition language (CDDL): a notational convention to
              express CBOR and JSON data structures", draft-ietf-cbor-
              cddl-07 (work in progress), February 2019.



Schaad                 Expires September 12, 2019               [Page 8]


Internet-Draft                 COSE X.509                     March 2019


   [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-12
              (work in progress), September 2018.

   [I-D.ietf-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-30 (work in progress),
              November 2018.

   [I-D.selander-ace-cose-ecdhe]
              Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
              Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
              cose-ecdhe-12 (work in progress), February 2019.

   [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,
              <https://www.rfc-editor.org/info/rfc2585>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [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>.

   [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>.

Author's Address

   Jim Schaad
   August Cellars

   Email: ietf@augustcellars.com











Schaad                 Expires September 12, 2019               [Page 9]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/