draft-ietf-ace-cwt-proof-of-possession-08.txt   draft-ietf-ace-cwt-proof-of-possession-09.txt 
ACE M. Jones ACE M. Jones
Internet-Draft Microsoft Internet-Draft Microsoft
Intended status: Standards Track L. Seitz Intended status: Standards Track L. Seitz
Expires: April 3, 2020 RISE SICS Expires: April 20, 2020 RISE SICS
G. Selander G. Selander
Ericsson AB Ericsson AB
S. Erdtman S. Erdtman
Spotify Spotify
H. Tschofenig H. Tschofenig
Arm Ltd. Arm Ltd.
October 1, 2019 October 18, 2019
Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs) Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)
draft-ietf-ace-cwt-proof-of-possession-08 draft-ietf-ace-cwt-proof-of-possession-09
Abstract Abstract
This specification describes how to declare in a CBOR Web Token (CWT) This specification describes how to declare in a CBOR Web Token (CWT)
that the presenter of the CWT possesses a particular proof-of- (which is defined by RFC 8392) that the presenter of the CWT
possession key. Being able to prove possession of a key is also possesses a particular proof-of-possession key. Being able to prove
sometimes described as being the holder-of-key. This specification possession of a key is also sometimes described as being the holder-
provides equivalent functionality to "Proof-of-Possession Key of-key. This specification provides equivalent functionality to
Semantics for JSON Web Tokens (JWTs)" (RFC 7800) but using CBOR and "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)" (RFC
CWTs rather than JSON and JWTs. 7800) but using Concise Binary Object Representation (CBOR) and CWTs
rather than JavaScript Object Notation (JSON) and JSON Web Tokens
(JWTs).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 3, 2020. This Internet-Draft will expire on April 20, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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7.2.2. Initial Registry Contents . . . . . . . . . . . . . . 12 7.2.2. Initial Registry Contents . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14
Document History . . . . . . . . . . . . . . . . . . . . . . . . 14 Document History . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
This specification describes how a CBOR Web Token (CWT) [CWT] can This specification describes how a CBOR Web Token (CWT) [RFC8392] can
declare that the presenter of the CWT possesses a particular proof- declare that the presenter of the CWT possesses a particular proof-
of-possession (PoP) key. Proof of possession of a key is also of-possession (PoP) key. Proof of possession of a key is also
sometimes described as being the holder-of-key. This specification sometimes described as being the holder-of-key. This specification
provides equivalent functionality to "Proof-of-Possession Key provides equivalent functionality to "Proof-of-Possession Key
Semantics for JSON Web Tokens (JWTs)" [RFC7800] but using CBOR Semantics for JSON Web Tokens (JWTs)" [RFC7800] but using Concise
[RFC7049] and CWTs [CWT] rather than JSON [RFC8259] and JWTs [JWT]. Binary Object Representation (CBOR) [RFC7049] and CWTs [RFC8392]
rather than JavaScript Object Notation (JSON) [RFC8259] and JSON Web
Tokens (JWTs) [JWT].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This specification uses terms defined in the CBOR Web Token (CWT) This specification uses terms defined in the CBOR Web Token (CWT)
[CWT], CBOR Object Signing and Encryption (COSE) [RFC8152], and [RFC8392], CBOR Object Signing and Encryption (COSE) [RFC8152], and
Concise Binary Object Representation (CBOR) [RFC7049] specifications. Concise Binary Object Representation (CBOR) [RFC7049] specifications.
These terms are defined by this specification: These terms are defined by this specification:
Issuer Issuer
Party that creates the CWT and binds the claims about the subject Party that creates the CWT and binds the claims about the subject
to the proof-of-possession key. to the proof-of-possession key.
Presenter Presenter
Party that proves possession of a private key (for asymmetric key Party that proves possession of a private key (for asymmetric key
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This specification provides examples in CBOR extended diagnostic This specification provides examples in CBOR extended diagnostic
notation, as defined in Appendix G of [RFC8610]. The examples notation, as defined in Appendix G of [RFC8610]. The examples
include line breaks for readability. include line breaks for readability.
3. Representations for Proof-of-Possession Keys 3. Representations for Proof-of-Possession Keys
By including a "cnf" (confirmation) claim in a CWT, the issuer of the By including a "cnf" (confirmation) claim in a CWT, the issuer of the
CWT declares that the presenter possesses a particular key and that CWT declares that the presenter possesses a particular key and that
the recipient can cryptographically confirm that the presenter has the recipient can cryptographically confirm that the presenter has
possession of that key. The value of the "cnf" claim is a CBOR map possession of that key. The value of the "cnf" claim is a CBOR map
and the members of that map identify the proof-of-possession key. (which is defined in Section 2.1 of [RFC7049]) and the members of
that map identify the proof-of-possession key.
The presenter can be identified in one of several ways by the CWT, The presenter can be identified in one of several ways by the CWT,
depending upon the application requirements. For instance, some depending upon the application requirements. For instance, some
applications may use the CWT "sub" (subject) claim [CWT], to identify applications may use the CWT "sub" (subject) claim [RFC8392], to
the presenter. Other applications may use the "iss" claim to identify the presenter. Other applications may use the "iss" claim
identify the presenter. In some applications, the subject identifier to identify the presenter. In some applications, the subject
might be relative to the issuer identified by the "iss" (issuer) identifier might be relative to the issuer identified by the "iss"
claim [CWT]. The actual mechanism used is dependent upon the (issuer) claim [RFC8392]. The actual mechanism used is dependent
application. The case in which the presenter is the subject of the upon the application. The case in which the presenter is the subject
CWT is analogous to Security Assertion Markup Language (SAML) 2.0 of the CWT is analogous to Security Assertion Markup Language (SAML)
[OASIS.saml-core-2.0-os] SubjectConfirmation usage. 2.0 [OASIS.saml-core-2.0-os] SubjectConfirmation usage.
3.1. Confirmation Claim 3.1. Confirmation Claim
The "cnf" claim in the CWT is used to carry confirmation methods. The "cnf" claim in the CWT is used to carry confirmation methods.
Some of them use proof-of-possession keys while others do not. This Some of them use proof-of-possession keys while others do not. This
design is analogous to the SAML 2.0 [OASIS.saml-core-2.0-os] design is analogous to the SAML 2.0 [OASIS.saml-core-2.0-os]
SubjectConfirmation element in which a number of different subject SubjectConfirmation element in which a number of different subject
confirmation methods can be included (including proof-of-possession confirmation methods can be included (including proof-of-possession
key information). key information).
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} }
} }
The COSE_Key MUST contain the required key members for a COSE_Key of The COSE_Key MUST contain the required key members for a COSE_Key of
that key type and MAY contain other COSE_Key members, including the that key type and MAY contain other COSE_Key members, including the
"kid" (Key ID) member. "kid" (Key ID) member.
The "COSE_Key" member MAY also be used for a COSE_Key representing a The "COSE_Key" member MAY also be used for a COSE_Key representing a
symmetric key, provided that the CWT is encrypted so that the key is symmetric key, provided that the CWT is encrypted so that the key is
not revealed to unintended parties. The means of encrypting a CWT is not revealed to unintended parties. The means of encrypting a CWT is
explained in [CWT]. If the CWT is not encrypted, the symmetric key explained in [RFC8392]. If the CWT is not encrypted, the symmetric
MUST be encrypted as described in Section 3.3. This procedure is key MUST be encrypted as described in Section 3.3. This procedure is
equivalent to the one defined in section 3.3 of [RFC7800]. equivalent to the one defined in section 3.3 of [RFC7800].
3.3. Representation of an Encrypted Symmetric Proof-of-Possession Key 3.3. Representation of an Encrypted Symmetric Proof-of-Possession Key
When the key held by the presenter is a symmetric key, the When the key held by the presenter is a symmetric key, the
"Encrypted_COSE_Key" member is an encrypted COSE_Key [RFC8152] "Encrypted_COSE_Key" member is an encrypted COSE_Key [RFC8152]
representing the symmetric key encrypted to a key known to the representing the symmetric key encrypted to a key known to the
recipient using COSE_Encrypt or COSE_Encrypt0. recipient using COSE_Encrypt or COSE_Encrypt0.
The following example illustrates a symmetric key that could The following example illustrates a symmetric key that could
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specified, as this is also protocol specific. specified, as this is also protocol specific.
Note that other means of proving possession of the key exist, which Note that other means of proving possession of the key exist, which
could be used in conjunction with a CWT's confirmation key. could be used in conjunction with a CWT's confirmation key.
Applications making use of such alternate means are encouraged to Applications making use of such alternate means are encouraged to
register them in the IANA "CWT Confirmation Methods" registry register them in the IANA "CWT Confirmation Methods" registry
established in Section 7.2. established in Section 7.2.
4. Security Considerations 4. Security Considerations
All the security considerations that are discussed in [CWT] also All the security considerations that are discussed in [RFC8392] also
apply here. In addition, proof of possession introduces its own apply here. In addition, proof of possession introduces its own
unique security issues. Possessing a key is only valuable if it is unique security issues. Possessing a key is only valuable if it is
kept secret. Appropriate means must be used to ensure that kept secret. Appropriate means must be used to ensure that
unintended parties do not learn private key or symmetric key values. unintended parties do not learn private key or symmetric key values.
Applications utilizing proof of possession SHOULD also utilize Applications utilizing proof of possession SHOULD also utilize
audience restriction, as described in Section 3.1.3 of [CWT], as it audience restriction, as described in Section 3.1.3 of [RFC8392], as
provides additional protections. Audience restriction can be used by it provides additional protections. Audience restriction can be used
recipients to reject messages intended for different recipients. by recipients to reject messages intended for different recipients.
(Of course, applications not using proof of possession can also
A recipient might not understand the "cnf" claim. Applications that benefit from using audience restriction to reject messages intended
use proof-of-possession keys in CWTs with the "cnf" claim MUST ensure for different recipients.)
that the parts of this specification that they use are implemented by
the intended recipient.
CBOR Web Tokens with proof-of-possession keys are used in context of CBOR Web Tokens with proof-of-possession keys are used in context of
an architecture, such as the ACE OAuth Framework an architecture, such as the ACE OAuth Framework
[I-D.ietf-ace-oauth-authz], in which protocols are used by a [I-D.ietf-ace-oauth-authz], in which protocols are used by a
presenter to request these tokens and to subsequently use them with presenter to request these tokens and to subsequently use them with
recipients. Proof of possession only provides the intended security recipients. Proof of possession only provides the intended security
gains when the proof is known to be current and not subject to replay gains when the proof is known to be current and not subject to replay
attacks; security protocols using mechanisms such as nonces and attacks; security protocols using mechanisms such as nonces and
timestamps can be used to avoid the risk of replay when performing timestamps can be used to avoid the risk of replay when performing
proof of possession for a token. Note that a discussion of the proof of possession for a token. Note that a discussion of the
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As is the case with other information included in a CWT, it is As is the case with other information included in a CWT, it is
necessary to apply data origin authentication and integrity necessary to apply data origin authentication and integrity
protection (via a keyed message digest or a digital signature). Data protection (via a keyed message digest or a digital signature). Data
origin authentication ensures that the recipient of the CWT learns origin authentication ensures that the recipient of the CWT learns
about the entity that created the CWT since this will be important about the entity that created the CWT since this will be important
for any policy decisions. Integrity protection prevents an adversary for any policy decisions. Integrity protection prevents an adversary
from changing any elements conveyed within the CWT payload. Special from changing any elements conveyed within the CWT payload. Special
care has to be applied when carrying symmetric keys inside the CWT care has to be applied when carrying symmetric keys inside the CWT
since those not only require integrity protection but also since those not only require integrity protection but also
confidentiality protection (e.g., either by encrypting the "cnf" confidentiality protection.
element, as specified in Section 3.3, or by encrypting the whole CWT,
as specified in [CWT]).
As described in Section 6 (Key Identification) and Appendix D (Notes As described in Section 6 (Key Identification) and Appendix D (Notes
on Key Selection) of [JWS], it is important to make explicit trust on Key Selection) of [JWS], it is important to make explicit trust
decisions about the keys. Proof-of-possession signatures made with decisions about the keys. Proof-of-possession signatures made with
keys not meeting the application's trust criteria MUST NOT be relied keys not meeting the application's trust criteria MUST NOT be relied
upon. upon.
5. Privacy Considerations 5. Privacy Considerations
A proof-of-possession key can be used as a correlation handle if the A proof-of-possession key can be used as a correlation handle if the
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able to represent the perspectives of different applications using able to represent the perspectives of different applications using
this specification in order to enable broadly informed review of this specification in order to enable broadly informed review of
registration decisions. In cases where a registration decision could registration decisions. In cases where a registration decision could
be perceived as creating a conflict of interest for a particular be perceived as creating a conflict of interest for a particular
Expert, that Expert should defer to the judgment of the other Expert, that Expert should defer to the judgment of the other
Experts. Experts.
7.1. CBOR Web Token Claims Registration 7.1. CBOR Web Token Claims Registration
This specification registers the "cnf" claim in the IANA "CBOR Web This specification registers the "cnf" claim in the IANA "CBOR Web
Token Claims" registry [IANA.CWT.Claims] established by [CWT]. Token Claims" registry [IANA.CWT.Claims] established by [RFC8392].
7.1.1. Registry Contents 7.1.1. Registry Contents
o Claim Name: "cnf" o Claim Name: "cnf"
o Claim Description: Confirmation o Claim Description: Confirmation
o JWT Claim Name: "cnf" o JWT Claim Name: "cnf"
o Claim Key: TBD (maybe 8) o Claim Key: TBD (maybe 8)
o Claim Value Type(s): map o Claim Value Type(s): map
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.1 of [[ this document ]] o Specification Document(s): Section 3.1 of [[ this document ]]
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o JWT Confirmation Method Name: "kid" o JWT Confirmation Method Name: "kid"
o Confirmation Key: 3 o Confirmation Key: 3
o Confirmation Value Type(s): binary string o Confirmation Value Type(s): binary string
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.4 of [[ this document ]] o Specification Document(s): Section 3.4 of [[ this document ]]
8. References 8. References
8.1. Normative References 8.1. Normative References
[CWT] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <http://www.rfc-editor.org/info/rfc8392>.
[IANA.CWT.Claims] [IANA.CWT.Claims]
IANA, "CBOR Web Token Claims", IANA, "CBOR Web Token Claims",
<http://www.iana.org/assignments/cwt>. <http://www.iana.org/assignments/cwt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
skipping to change at page 13, line 27 skipping to change at page 13, line 22
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017, RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>. <https://www.rfc-editor.org/info/rfc8152>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
8.2. Informative References 8.2. Informative References
[I-D.ietf-ace-oauth-authz] [I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0 Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-21 Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-21
(work in progress), February 2019. (work in progress), February 2019.
[IANA.JWT.Claims] [IANA.JWT.Claims]
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[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>. June 2019, <https://www.rfc-editor.org/info/rfc8610>.
Acknowledgements Acknowledgements
Thanks to the following people for their reviews of the Thanks to the following people for their reviews of the
specification: Roman Danyliw, Benjamin Kaduk, Michael Richardson, and specification: Roman Danyliw, Christer Holmberg, Benjamin Kaduk, Yoav
Jim Schaad. Nir, Michael Richardson, and Jim Schaad.
Ludwig Seitz and Goeran Selander worked on this document as part of Ludwig Seitz and Goeran Selander worked on this document as part of
the CelticPlus projects CyberWI and CRITISEC, with funding from the CelticPlus projects CyberWI and CRITISEC, with funding from
Vinnova. Vinnova.
Document History Document History
[[ to be removed by the RFC Editor before publication as an RFC ]] [[ to be removed by the RFC Editor before publication as an RFC ]]
-09
o Addressed Gen-ART review comments by Christer Holmberg and SecDir
review comments by Yoav Nir.
-08 -08
o Addressed remaining Area Director review comments by Benjamin o Addressed remaining Area Director review comments by Benjamin
Kaduk. Kaduk.
-07 -07
o Addressed Area Director review by Benjamin Kaduk. o Addressed Area Director review by Benjamin Kaduk.
-06 -06
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