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Versions: 00

CoRE Working Group                                           H. Birkholz
Internet-Draft                                            Fraunhofer SIT
Intended status: Informational                                C. Bormann
Expires: January 2, 2019                         Universitaet Bremen TZI
                                                             M. Pritikin
                                                                   Cisco
                                                            R. Moskowitz
                                                                  Huawei
                                                           July 01, 2018


                           Concise Identities
                      draft-birkholz-core-coid-00

Abstract

   There is an increased demand of trustworthy claim sets -- a set of
   system entity characteristics tied to an entity via signatures -- in
   order to provide information.  Claim sets represented via CBOR Web
   Tokens (CWT) can compose a variety of evidence suitable for
   constrained-node networks and to support secure device automation.
   This document focuses on sets of identifiers and attributes that are
   tied to a system entity and are typically used to compose identities
   appropriate for Constrained RESTful Environment (CoRE) authentication
   needs.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on January 2, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Claims in a Concise Identity  . . . . . . . . . . . . . . . .   4
     2.1.  iss: CWT issuer . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  sub: CWT subject  . . . . . . . . . . . . . . . . . . . .   5
     2.3.  aud: CWT audience . . . . . . . . . . . . . . . . . . . .   5
     2.4.  exp: CWT expiration time  . . . . . . . . . . . . . . . .   5
     2.5.  nbf: CWT start of validity  . . . . . . . . . . . . . . .   5
     2.6.  iat: CWT time of issue  . . . . . . . . . . . . . . . . .   5
     2.7.  cti: CWT ID . . . . . . . . . . . . . . . . . . . . . . .   5
     2.8.  cnf: CWT proof-of-possession key claim  . . . . . . . . .   5
   3.  Signature Envelope  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Processing Rules  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Examples of claims taken from IEEE 802.1AR
                identifiers  . . . . . . . . . . . . . . . . . . . .   7
     A.1.  7.2.1 version . . . . . . . . . . . . . . . . . . . . . .   8
     A.2.  7.2.2 serialNumber  . . . . . . . . . . . . . . . . . . .   8
     A.3.  7.2.3 signature . . . . . . . . . . . . . . . . . . . . .   8
     A.4.  7.2.4 issuer Name . . . . . . . . . . . . . . . . . . . .   8
     A.5.  7.2.5 authoritykeyidentifier  . . . . . . . . . . . . . .   8
     A.6.  7.2.7.1 notBefore . . . . . . . . . . . . . . . . . . . .   8
     A.7.  7.2.7.2 notAfter  . . . . . . . . . . . . . . . . . . . .   8
     A.8.  7.2.8 subject . . . . . . . . . . . . . . . . . . . . . .   9
     A.9.  7.2.10 subjectPublicKeyInfo . . . . . . . . . . . . . . .   9
     A.10. 7.2.11 signatureAlgorithm . . . . . . . . . . . . . . . .   9
     A.11. 7.2.12 signatureValue . . . . . . . . . . . . . . . . . .   9
   Appendix B.  Examples of claims taken from X.509 certificates . .   9
     B.1.  2.5.29.35 - Authority Key Identifier  . . . . . . . . . .   9
     B.2.  2.5.29.14 - Subject Key Identifier  . . . . . . . . . . .   9
     B.3.  2.5.29.15 - Key Usage . . . . . . . . . . . . . . . . . .   9
     B.4.  2.5.29.37 - Extended key usage  . . . . . . . . . . . . .  10



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     B.5.  1.3.6.1.5.5.7.1.1 - Authority Information Access  . . . .  10
     B.6.  1.3.6.1.4.1.311.20.2 - Certificate Template Name Domain
           Controller (Microsoft)  . . . . . . . . . . . . . . . . .  10
   Appendix C.  Graveyard  . . . . . . . . . . . . . . . . . . . . .  10
     C.1.  7.2.9 subjectAltName  . . . . . . . . . . . . . . . . . .  10
     C.2.  7.2.13 extensions . . . . . . . . . . . . . . . . . . . .  10
     C.3.  2.5.29.31 - CRL Distribution Points . . . . . . . . . . .  10
     C.4.  2.5.29.17 - Subject Alternative Name  . . . . . . . . . .  10
     C.5.  2.5.29.19 - Basic Constraints . . . . . . . . . . . . . .  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   X.509 certificates [RFC5280] and Secure Device Identifier
   [IEEE-802.1AR] are ASN.1 encoded identity documents and intended to
   be tied to a system entity uniquely identified via these identity
   documents.  An identity document - a certificate - can be conveyed to
   other system entities in order to prove the identity of the owner of
   the identity document.  Trust in the proof can be established by
   mutual trust of the provider and assessor of the identity in a third
   party verification (TVP) provided, for example, by a certificate
   authority (CA) or its subsidiaries (sub CA).

   The evidence a certificate comprises is typically composed of a set
   of claims that is signed using secret keys issued by a (sub) CA.  The
   core set of claims included in a certificate - its attributes - are
   well defined in the X.509v3 specifications and IEEE 802.1AR.

   This document summarizes the core set of attributes and provides a
   corresponding list of claims using concise integer labels to be used
   in claim sets for CBOR Web Tokens (CWT) [RFC8392].  A resulting
   Concise Identity (CoID) is able to represent a signed set of claims
   that composes an Identity as defined in [RFC4949].

   The objective of using CWT as a basis for the signed claim sets
   defined in this document is to gain more flexibility and at the same
   time more rigorously defined semantics for the signed claim sets.  In
   addition, the benefits of using CBOR, COSE, and the corresponding CWT
   structure accrue, including more compact encoding and a simpler
   implementation in contrast to classical ASN.1 (DER/BER/PEM)
   structures and the X.509 complexity and uncertainty that has accreted
   since X.509 was released 29 years ago.  One area where both the
   compactness and the definiteness are highly desirable is in
   Constrained-Node Networks [RFC7228], which may also make use of the
   Constrained Application Protocol (CoAP, [RFC7252]); however, the area
   of application of Concise Identities is not limited to constrained-
   node networks.



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   The present version of this document is a strawman that attempts to
   indicate the direction the work is intended to take.  Not all
   inspirations this version takes from X.509 maybe need to be taken.

1.1.  Terminology

   This document uses terminology from [RFC8392] and therefore also
   [RFC7519], as well as from [RFC8152].  Specifically, we note:

   Claim:  A piece of information asserted about a subject.  A claim is
      represented as a name/value pair consisting of a Claim Name and a
      Claim Value.

   Claims are grouped into claims sets (represented here by a CWT),
   which need to be interpreted as a whole.  Note that this usage is a
   bit different from idiomatic English usage, where a claim would stand
   on its own.

   (Note that the current version of this draft is not very explicit
   about the relationship of identities and identifiers.  To be done in
   next version.)

2.  Claims in a Concise Identity

   A Concise Identity (CoID) is a CBOR Web Token [RFC8392] with certain
   claims present.  It can be signed in a number of ways, including a
   COSE_Sign1 data object [RFC8152].

2.1.  iss: CWT issuer

   Optional: identifies the principal that is the claimant for the
   claims in the CoID ([RFC8392] Section 3.1.1, cf. Section 4.1.1 in
   [RFC7519]).

   o  Note that this is a StringOrURI (if it contains a ":" it needs to
      be a URI)

   o  For the "string" case (no ":"), there is no way to extract
      meaningful components from the string

   o  Make it a URI if it needs to be structured (not for routine
      retrieval, unless specified so by an application)

   o  If this URI looks like an HTTP or HTTPS URI then something
      retrievable by humans should exist there.

   o  Alternatively, some arithmetic can be applied to the URI (extract
      origin, add /.well-known/...) to find relevant information.



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2.2.  sub: CWT subject

   Optional: identifies the principal that is the subject for the claims
   in the CoID ([RFC8392] Section 3.1.2, cf. Section 4.1.2 in
   [RFC7519]).

2.3.  aud: CWT audience

   Optional: identifies the recipients that the CoID is intended for
   ([RFC8392] Section 3.1.4, cf. Section 4.1.4 in [RFC7519]).

2.4.  exp: CWT expiration time

   Optional: the time on or after which the CoID must no longer be
   accepted for processing ([RFC8392] Section 3.1.4, cf. Section 4.1.4
   in [RFC7519]).

2.5.  nbf: CWT start of validity

   Optional: the time before which the CoID must not be accepted for
   processing ([RFC8392] Section 3.1.5, cf. Section 4.1.5 in [RFC7519]).

2.6.  iat: CWT time of issue

   Optional: the creation time of the CoID ([RFC8392] Section 3.1.6, cf.
   Section 4.1.6 in [RFC7519]).

2.7.  cti: CWT ID

   The "cti" (CWT ID) claim provides a unique identifier for the CoID
   ([RFC8392] Section 3.1.7, cf. "jti" in Section 4.1.7 in [RFC7519]).

   CWT IDs are intended to be unique within an application, so they need
   to be either coordinated between issuers or based on sufficient
   randomness (e.g., 112 bits or more).

2.8.  cnf: CWT proof-of-possession key claim

   The "cnf" claim identifies the key that can be used by the subject
   for proof-of-possession and provides parameters to identify the CWT
   Confirmation Method ([I-D.ietf-ace-cwt-proof-of-possession]
   Section 3.1).

3.  Signature Envelope

   The signature envelope [TBD: need not actually be envelope, may be
   detached, too] carries additional information, e.g., the signature,
   as well as the identification of the signature algorithm employed



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   (COSE: alg).  Additional information may pertain to the signature (as
   opposed to the claims being signed), e.g., a key id (COSE: kid) may
   be given in the header of the signature.

4.  Processing Rules

   (TBD: This should contain some discussion of the processing rules
   that apply for CoIDs.  Some of this will just be pointers to
   [I-D.ietf-oauth-jwt-bcp].)

5.  IANA Considerations

   This document makes no requests of IANA

6.  Security Considerations

7.  References

7.1.  Normative References

   [I-D.ietf-ace-cwt-proof-of-possession]
              Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
              possession-03 (work in progress), June 2018.

   [I-D.ietf-oauth-jwt-bcp]
              Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", draft-ietf-oauth-jwt-bcp-03 (work in
              progress), May 2018.

   [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>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [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>.



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7.2.  Informative References

   [IEEE-802.1AR]
              "ISO/IEC/IEEE International Standard for Information
              technology -- Telecommunications and information exchange
              between systems -- Local and metropolitan area networks --
              Part 1AR: Secure device identity", IEEE standard,
              DOI 10.1109/ieeestd.2014.6739984, n.d..

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
              <https://www.rfc-editor.org/info/rfc4949>.

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

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

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

Appendix A.  Examples of claims taken from IEEE 802.1AR identifiers

   This appendix briefly discusses common fields in a X.509 certificate
   or an IEEE 802.1AR Secure Device Identifier and relates them to
   claims in a CoID.

   The original purpose of X.509 was only to sign the association
   between a name and a public key.  In principle, if something else
   needs to be signed as well, CMS [RFC5652] is required.  This
   principle has not been strictly upheld over time; this is
   demonstrated by the growth of various extensions to X.509
   certificates that might or might not be interpreted to carry various
   additional claims.

   This document details only the claim sets for CBOR Web Tokens that
   are necessary for authentication.  The plausible integration or
   replacement of ASN.1 formats in enrollment procotols, [D]TLS
   handshakes and similar are not in scope of this document.






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   Subsections in this appendix are marked by the ASN.1 Object
   Identifier (OID) typically used for the X.509 item.  [TODO: Make this
   true; there are still some section numbers.]

A.1.  7.2.1 version

   The version field is typically not employed usefully in an X.509
   certificate, except possibly in legacy applications that accept
   original (pre-v3) X.509 certificates.

   Generally, the point of versioning is to deliberately inhibit
   interoperability (due to semantic meaning changes).  CoIDs do not
   employ versioning.  Where future work requires semantic changes,
   these will be expressed by making alternate kinds of claims.

A.2.  7.2.2 serialNumber

   Covered by cti claim.

A.3.  7.2.3 signature

   The signature, as well as the identification of the signature
   algorithm, are provided by the COSE container (e.g., COSE_Sign1) used
   to sign the CoID's CWT.

A.4.  7.2.4 issuer Name

   Covered by iss claim.

A.5.  7.2.5 authoritykeyidentifier

   Covered by COSE kid in signature, if needed.

A.6.  7.2.7.1 notBefore

   Covered by nbf claim.

A.7.  7.2.7.2 notAfter

   Covered by exp claim.

   For Secured Device identifiers, this claim is typically left out.

   o  get a new one whenver you think you need it ("normal path")

   o  nonced ocsp? might benefit from a more lightweight freshness
      verification of existing signed assertion - exploration required!




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   o  (first party only verfiable freshness may be cheaper than third-
      party verifiable?)

A.8.  7.2.8 subject

   Covered by sub claim.

   Note that if claim sets need to be made about multiple subjects, the
   favored approach in CoID is to create multiple CoIDs, one each per
   subject.

A.9.  7.2.10 subjectPublicKeyInfo

   Covered by cnf claim.

A.10.  7.2.11 signatureAlgorithm

   In COSE_Sign1 envelope.

A.11.  7.2.12 signatureValue

   In COSE_Sign1 envelope.

Appendix B.  Examples of claims taken from X.509 certificates

   Most claims in X.509 certificates take the form of certificate
   extensions.  This section reviews a few common (and maybe not so
   common) certificate extensions and assesses their usefulness in
   signed claim sets.

B.1.  2.5.29.35 - Authority Key Identifier

   Used in certificate chaining.  Can be mapped to COSE "kid" of the
   issuer.

B.2.  2.5.29.14 - Subject Key Identifier

   Used in certificate chaining.  Can be mapped to COSE "kid" in the
   "cnf" (see Section 3.4 of [I-D.ietf-ace-cwt-proof-of-possession]).

B.3.  2.5.29.15 - Key Usage

   Usage information for a key claim that is included in the signed
   claims.  Can be mapped to COSE "key_ops" [TBD: Explain details].







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B.4.  2.5.29.37 - Extended key usage

   Can include additional usage information such as 1.3.6.1.5.5.7.3.1
   for TLS server certificates or 1.3.6.1.5.5.7.3.2 for TLS client
   certificates.

B.5.  1.3.6.1.5.5.7.1.1 - Authority Information Access

   More information about the signer.  May include a pointer to signers
   higher up in the certificate chain (1.3.6.1.5.5.7.48.2), typically in
   the form of a URI to their certificate.

B.6.  1.3.6.1.4.1.311.20.2 - Certificate Template Name Domain Controller
      (Microsoft)

   This is an example for many ill-defined extensions that are on some
   arcs of the OID space somewhere.

   E.g., the UCS-2 string (ASN.1 BMPString) "IPSECIntermediateOffline"

Appendix C.  Graveyard

C.1.  7.2.9 subjectAltName

   (See "sub").

C.2.  7.2.13 extensions

   Extensions are handled by adding CWT claims to the CWT.

C.3.  2.5.29.31 - CRL Distribution Points

   Usually URIs of places where a CRL germane to the certificate can be
   obtained.  Other forms of validating claim sets may be more
   appropriate than CRLs for the applications envisaged here.

   (Might be replaced by a more general freshness verification approach
   later.  For example one could define a generic "is this valid"
   request to an authority.)

C.4.  2.5.29.17 - Subject Alternative Name

   Additional names for the Subject.

   These may be an "OtherName", i.e. a mistery blob "defined by" an
   ASN.1 OID such as 1.3.6.1.4.1.9.21.2.3, or one out of a few formats
   such as URIs (which may, then, turn out not to be really URIs).
   Naming subjects obviously is a major issue that needs attention.



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C.5.  2.5.29.19 - Basic Constraints

   Can identify the key claim as that for a CA, and can limit the length
   of a certificate path.  Empty in all the examples analyzed.

   Any application space can define new fields / claims as appropriate
   and use them.  There is no need for the underlying structure to
   define an additional extension method for this.  Instead, they can
   use the registry as defined in Section 9.1 of [RFC8392].>

Acknowledgements

Authors' Addresses

   Henk Birkholz
   Fraunhofer SIT
   Rheinstrasse 75
   Darmstadt  64295
   Germany

   Email: henk.birkholz@sit.fraunhofer.de


   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org


   Max Pritikin
   Cisco

   Email: pritikin@cisco.com


   Robert Moskowitz
   Huawei
   Oak Park, MI  48237

   Email: rgm@labs.htt-consult.com







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