Last Call Review of draft-ietf-jose-jwk-thumbprint-05
review-ietf-jose-jwk-thumbprint-05-secdir-lc-montville-2015-06-10-00

Hi,

I have reviewed this document as part of the security directorate's ongoing
effort to review all IETF documents being processed by the IESG. These comments
were written primarily for the benefit of the security area directors. Document
editors and WG chairs should treat these comments just like any other last call
comments.

I believe the document is ready with (potential) issues.  The “with issues”
might be due to ignorance on my part.  The draft does a very good job of
explaining the canonical form of a JSON Web Key that can be used for
establishing a thumbprint under varying circumstances, complete with what I
found to be helpful examples.

The primary issue I have is that it’s unclear how relying parties are going to
know which hash algorithm has been used.  The examples use SHA-256, but I’m not
seeing where SHA-256 might be specified as a MUST or even a SHOULD.  Moreover,
the example output ultimately shows only the Base-64 encoding of the resulting
hash, which says nothing about the algorithm used to identify a key.

Additionally, in Section 4, “JSON and Unicode Considerations” some “should”s
are used, but I’m not reading them as SHOULDs.  Should they be SHOULDs?  For
example, the start of the third paragraph in that section: “if new JWK members
are defined that use non-ASCII member names, their definitions should specify
the exact Unicode code point sequences used to represent them.”  It’s not clear
to me whether this is a strong statement or just a recommendation - it seems
that this draft could help the future by making stronger statements to
encourage future interoperability.

Kind regards,

Adam