--- 1/draft-ietf-ace-cwt-proof-of-possession-08.txt 2019-10-18 16:13:07.021806284 -0700 +++ 2/draft-ietf-ace-cwt-proof-of-possession-09.txt 2019-10-18 16:13:07.053807097 -0700 @@ -1,52 +1,54 @@ ACE M. Jones Internet-Draft Microsoft Intended status: Standards Track L. Seitz -Expires: April 3, 2020 RISE SICS +Expires: April 20, 2020 RISE SICS G. Selander Ericsson AB S. Erdtman Spotify H. Tschofenig Arm Ltd. - October 1, 2019 + October 18, 2019 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 This specification describes how to declare in a CBOR Web Token (CWT) - that the presenter of the CWT possesses a particular proof-of- - possession key. Being able to prove possession of a key is also - sometimes described as being the holder-of-key. This specification - provides equivalent functionality to "Proof-of-Possession Key - Semantics for JSON Web Tokens (JWTs)" (RFC 7800) but using CBOR and - CWTs rather than JSON and JWTs. + (which is defined by RFC 8392) that the presenter of the CWT + possesses a particular proof-of-possession key. Being able to prove + possession of a key is also sometimes described as being the holder- + of-key. This specification provides equivalent functionality to + "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)" (RFC + 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 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 April 3, 2020. + This Internet-Draft will expire on April 20, 2020. Copyright Notice Copyright (c) 2019 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -78,38 +80,40 @@ 7.2.2. Initial Registry Contents . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 13 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14 Document History . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 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- of-possession (PoP) key. Proof of possession of a key is also sometimes described as being the holder-of-key. This specification provides equivalent functionality to "Proof-of-Possession Key - Semantics for JSON Web Tokens (JWTs)" [RFC7800] but using CBOR - [RFC7049] and CWTs [CWT] rather than JSON [RFC8259] and JWTs [JWT]. + Semantics for JSON Web Tokens (JWTs)" [RFC7800] but using Concise + Binary Object Representation (CBOR) [RFC7049] and CWTs [RFC8392] + rather than JavaScript Object Notation (JSON) [RFC8259] and JSON Web + Tokens (JWTs) [JWT]. 2. 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. 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. These terms are defined by this specification: Issuer Party that creates the CWT and binds the claims about the subject to the proof-of-possession key. Presenter Party that proves possession of a private key (for asymmetric key @@ -127,32 +131,33 @@ This specification provides examples in CBOR extended diagnostic notation, as defined in Appendix G of [RFC8610]. The examples include line breaks for readability. 3. Representations for Proof-of-Possession Keys By including a "cnf" (confirmation) claim in a CWT, the issuer of the CWT declares that the presenter possesses a particular key and that the recipient can cryptographically confirm that the presenter has 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, depending upon the application requirements. For instance, some - applications may use the CWT "sub" (subject) claim [CWT], to identify - the presenter. Other applications may use the "iss" claim to - identify the presenter. In some applications, the subject identifier - might be relative to the issuer identified by the "iss" (issuer) - claim [CWT]. The actual mechanism used is dependent upon the - application. The case in which the presenter is the subject of the - CWT is analogous to Security Assertion Markup Language (SAML) 2.0 - [OASIS.saml-core-2.0-os] SubjectConfirmation usage. + applications may use the CWT "sub" (subject) claim [RFC8392], to + identify the presenter. Other applications may use the "iss" claim + to identify the presenter. In some applications, the subject + identifier might be relative to the issuer identified by the "iss" + (issuer) claim [RFC8392]. The actual mechanism used is dependent + upon the application. The case in which the presenter is the subject + of the CWT is analogous to Security Assertion Markup Language (SAML) + 2.0 [OASIS.saml-core-2.0-os] SubjectConfirmation usage. 3.1. Confirmation Claim 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 design is analogous to the SAML 2.0 [OASIS.saml-core-2.0-os] SubjectConfirmation element in which a number of different subject confirmation methods can be included (including proof-of-possession key information). @@ -216,22 +221,22 @@ } } 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 "kid" (Key ID) member. 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 not revealed to unintended parties. The means of encrypting a CWT is - explained in [CWT]. If the CWT is not encrypted, the symmetric key - MUST be encrypted as described in Section 3.3. This procedure is + explained in [RFC8392]. If the CWT is not encrypted, the symmetric + key MUST be encrypted as described in Section 3.3. This procedure is equivalent to the one defined in section 3.3 of [RFC7800]. 3.3. Representation of an Encrypted Symmetric Proof-of-Possession Key When the key held by the presenter is a symmetric key, the "Encrypted_COSE_Key" member is an encrypted COSE_Key [RFC8152] representing the symmetric key encrypted to a key known to the recipient using COSE_Encrypt or COSE_Encrypt0. The following example illustrates a symmetric key that could @@ -333,35 +338,33 @@ specified, as this is also protocol specific. Note that other means of proving possession of the key exist, which could be used in conjunction with a CWT's confirmation key. Applications making use of such alternate means are encouraged to register them in the IANA "CWT Confirmation Methods" registry established in Section 7.2. 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 unique security issues. Possessing a key is only valuable if it is kept secret. Appropriate means must be used to ensure that unintended parties do not learn private key or symmetric key values. Applications utilizing proof of possession SHOULD also utilize - audience restriction, as described in Section 3.1.3 of [CWT], as it - provides additional protections. Audience restriction can be used by - recipients to reject messages intended for different recipients. - - A recipient might not understand the "cnf" claim. Applications that - use proof-of-possession keys in CWTs with the "cnf" claim MUST ensure - that the parts of this specification that they use are implemented by - the intended recipient. + audience restriction, as described in Section 3.1.3 of [RFC8392], as + it provides additional protections. Audience restriction can be used + by recipients to reject messages intended for different recipients. + (Of course, applications not using proof of possession can also + benefit from using audience restriction to reject messages intended + for different recipients.) CBOR Web Tokens with proof-of-possession keys are used in context of an architecture, such as the ACE OAuth Framework [I-D.ietf-ace-oauth-authz], in which protocols are used by a presenter to request these tokens and to subsequently use them with recipients. Proof of possession only provides the intended security gains when the proof is known to be current and not subject to replay attacks; security protocols using mechanisms such as nonces and timestamps can be used to avoid the risk of replay when performing proof of possession for a token. Note that a discussion of the @@ -370,23 +373,21 @@ As is the case with other information included in a CWT, it is necessary to apply data origin authentication and integrity protection (via a keyed message digest or a digital signature). Data origin authentication ensures that the recipient of the CWT learns about the entity that created the CWT since this will be important for any policy decisions. Integrity protection prevents an adversary from changing any elements conveyed within the CWT payload. Special care has to be applied when carrying symmetric keys inside the CWT since those not only require integrity protection but also - confidentiality protection (e.g., either by encrypting the "cnf" - element, as specified in Section 3.3, or by encrypting the whole CWT, - as specified in [CWT]). + confidentiality protection. As described in Section 6 (Key Identification) and Appendix D (Notes on Key Selection) of [JWS], it is important to make explicit trust decisions about the keys. Proof-of-possession signatures made with keys not meeting the application's trust criteria MUST NOT be relied upon. 5. Privacy Considerations A proof-of-possession key can be used as a correlation handle if the @@ -456,21 +457,21 @@ able to represent the perspectives of different applications using this specification in order to enable broadly informed review of registration decisions. In cases where a registration decision could be perceived as creating a conflict of interest for a particular Expert, that Expert should defer to the judgment of the other Experts. 7.1. CBOR Web Token Claims Registration 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 o Claim Name: "cnf" o Claim Description: Confirmation o JWT Claim Name: "cnf" o Claim Key: TBD (maybe 8) o Claim Value Type(s): map o Change Controller: IESG o Specification Document(s): Section 3.1 of [[ this document ]] @@ -541,24 +542,20 @@ o JWT Confirmation Method Name: "kid" o Confirmation Key: 3 o Confirmation Value Type(s): binary string o Change Controller: IESG o Specification Document(s): Section 3.4 of [[ this document ]] 8. 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, . - [IANA.CWT.Claims] IANA, "CBOR Web Token Claims", . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object @@ -571,20 +568,24 @@ . [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . + [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, + "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, + May 2018, . + 8.2. Informative References [I-D.ietf-ace-oauth-authz] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "Authentication and Authorization for Constrained Environments (ACE) using the OAuth 2.0 Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-21 (work in progress), February 2019. [IANA.JWT.Claims] @@ -618,31 +619,36 @@ [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019, . Acknowledgements Thanks to the following people for their reviews of the - specification: Roman Danyliw, Benjamin Kaduk, Michael Richardson, and - Jim Schaad. + specification: Roman Danyliw, Christer Holmberg, Benjamin Kaduk, Yoav + Nir, Michael Richardson, and Jim Schaad. Ludwig Seitz and Goeran Selander worked on this document as part of the CelticPlus projects CyberWI and CRITISEC, with funding from Vinnova. Document History [[ 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 o Addressed remaining Area Director review comments by Benjamin Kaduk. -07 o Addressed Area Director review by Benjamin Kaduk. -06