Concise Identities
draft-birkholz-core-coid-00
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| Authors | Henk Birkholz , Carsten Bormann , Max Pritikin , Robert Moskowitz | ||
| Last updated | 2018-07-02 | ||
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draft-birkholz-core-coid-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.
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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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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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