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JWT URI
draft-chadwick-oauth-jwk-uri-00

Document Type Active Internet-Draft (individual)
Author David W Chadwick
Last updated 2022-02-09
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draft-chadwick-oauth-jwk-uri-00
OAuth Working Group                                 D.W.Chadwick
Internet Draft                           Crossword Cybersecurity
Intended status: Proposed Standard              February 9, 2022
Expires: August 9, 2022        

                        JWT URI
         draft-chadwick-oauth-jwk-uri-00.txt
      

Status of This Memo

This is an Internet Standards Track document.

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This Internet-Draft will expire on August 9, 2022.

Copyright Notice

Copyright (c) 2022 IETF Trust and the persons identified as the 
document authors. All rights reserved.

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respect to this document.

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Abstract

This specification registers a kind of URI that represents a JSON 
Web Key (JWK) value. This enables JWKs to be used, for instance, as 
key identifiers in contexts requiring URIs.

Table of Contents

1. Introduction................................2

2. Requirements Notation and Conventions.......2

3. JWK URI.....................................3

4. Comparison of JWK URIs with JWK Thumbprint URIs...3

5. Security Considerations................4

6. IANA Considerations....................4

7. References..............................4

7.1. Normative References..................4

7.2. Informative References.................5

8. Acknowledgments..........................5

Appendix A. Document History................6

1. Introduction
    
A JSON Web Key (JWK) [RFC7517] is a JavaScript Object Notation (JSON) 
data structure that represents a cryptographic key.

This specification defines a URI prefix indicating that the portion 
of the URI following the prefix is a JWK. This enables JWKs to be  
communicated in contexts requiring URIs, including in specific JSON 
Web Token (JWT) [RFC7519] claims.

JWK URIs are proposed to be used in the [SIOPv2] specification as 
one kind of subject identifier in a context requiring that the 
identifier be a URI. In this case, the subject identifier is derived 
from a public key represented as a JWK. Expressing the identifier as 
a JWK URI enables this kind of identifier to be differentiated from 
other kinds of identifiers that are also URIs, such as Decentralized 
Identifiers (DIDs) [DID-Core].

 

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2. Requirements Notation and Conventions

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.

3. JWK URI

The following URI prefix is defined to indicate that the portion of 
the URI following the prefix is a JWK:

    o "urn:ietf:params:oauth:jwk"

The prefix MUST be followed by a colon and a JWK value that is formed by 
performing a base64 encoding of the JWK to form a URI representing a 
JWK.

4. Comparison of JWK URIs with JWK Thumbprint URIs

To produce or validate a JWK Thumbprint, both the sender and the 
receiver have to have the JWK available to them. Then they have to 
canonicalise the JWK as described in [RFC7638], and finally hash the 
octets of the UTF-8 representation of this JSON object with a pre-
agreed algorithm in order to both obtain the same hash value. The 
way that the JWK Thumbprint URI is used in SIOPv2 [SIOPv2] is as 
follows:

1. the SIOP creates an asymmetric key pair and encodes the public 
key as a JWK

2. the SIOP creates the JWK Thumbprint as described in [RFC7638] and 
converts it to a URI as described in [JONES]

3. the SIOP passes both the JWK and JWK Thumbprint URI to the RP in 
the JWT

4. the RP extracts the JWK and JWK Thumbprint from the JWT

5. the RP re-computes the JWK Thumbprint from the JWK

6. the RP compares the computed JWK Thumbprint with the received JWK 
Thumbprint to confirm that they are equal.

 

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One can see that the use of JWK Thumbprint URIs is both inefficient 
(in all cases) and a significant disadvantage (in some cases). If 
the JWK URI (as described in this document) is transferred instead 
of the JWK and JWK Thumbprint URI then:

a) The SIOP will never need to create the JWK Thumbprint URI. The RP 
may only need to create the JWK Thumbprint if it needs this, for 
example, as a unique subject identifier. Even in this case, there is 
still an advantage to the RP in receiving the JWK URI instead of the 
JWK Thumbprint URI, in that the RP no longer needs to pre-agree a 
hashing algorithm with the SIOP. Thus the RP can independently 
determine which hashing algorithm to use when creating its own JWK 
Thumbprint. 
(Note. If the SIOP were able to canonicalise the same 
public key in a JWK in different ways and produce different 
thumbprints from the same public key, then the canonicalisation 
algorithm is broken, and the RP would never to able to 
deterministically produce the same thumbprints each time.)

b) In those cases where the SIOP uses ephemeral key pairs and a 
different public key each time it communicates with an RP, then 
neither party needs to produce the JWK Thumbprint as it will never 
be seen again. It is a significant disadvantage to have to use JWK 
Thumbprints in this case.

One possible disadvantage of using JWK URIs instead of JWK 
Thumbprint URIs is the resulting increase in size of the JWT. Base 
64 encoding a JWK string increases its size by 33%. However this 
increase in JWT size is offset by the decrease in size by not 
needing to include the JWT thumbprint URI as well as the JWK. The 
trade off is the processing of JWKs to produce thumbprints by the 
sender and receiver versus the overhead of transferring larger JWTs.

5. Security Considerations

The security considerations of [RFC7638] will apply when the RP is 
using [RFC7638] to produce thumbprints.

 

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6. IANA Considerations

6.1. OAuth URI Registration

This specification proposes to register the following value in the 
IANA "OAuth URI" registry [IANA.OAuth.Parameters] established by 
[RFC6755].

6.1.1. Registry Contents

o URN: urn:ietf:params:oauth:jwk

o Common Name: JWK URI

o Change controller: IESG

o Specification Document: [[ this specification ]]

7. References

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 
Requirement Levels", BCP 14, RFC 2119, March 1997.

[IANA.OAuth.Parameters] IANA, "OAuth Parameters", 
<http://www.iana.org/assignments/oauth-parameters>.

[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.rfceditor.org/info/rfc2119>.

[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK) 
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September 
2015, <https://www.rfc-editor.org/info/rfc7638>.

[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>.

 

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7.2. Informative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 
Requirement Levels", BCP 14, RFC 2119, March 1997.

[DID-Core] Sporny, M., Guy, A., Sabadello, M., and D. Reed, 
"Decentralized Identifiers (DIDs) v1.0", Aug 2021, 
<https://www.w3.org/TR/2021/PR-did-core-20210803/>.

[RFC6755] Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace 
for OAuth", RFC 6755, DOI 10.17487/RFC6755, October 2012, 
<https://www.rfc-editor.org/info/rfc6755>.

[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 
10.17487/RFC7517, May 2015, 
<https://www.rfceditor.org/info/rfc7517>.

[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>.

[SIOPv2] Yasuda, K. and M. B. Jones, "Self-Issued OpenID Provider 
v2", December 2021, 
<https://openid.net/specs/openidconnect-self-issued-v2-1_0.html>.

[JONES] Yasuda, K., Jones, M., "JWK Thumbprint URK", Internet
Draft draft-ietf-oauth-jwk-thumbprint-uri-00

8. Acknowledgments

to be done.

Appendix A. Document History

[[ to be removed by the RFC Editor before publication as an 
RFC ]] 

-00

o Created initial draft.

Authors' Addresses

David W Chadwick
Crossword Cybersecurity
Email: david.chadwick@crosswordcybersecurity.com
URI: https://www.linkedin.com/in/davidwchadwick/

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