Re: [openpgp] v5 interoperability

[Andrew Gallagher <[e-mail]>]

On 16 Apr 2024, at 08:35, Werner Koch <[e-mail]> wrote:

On Mon, 15 Apr 2024 11:31, Andrew Gallagher said:

will gnupg reject v4 pqc keys if they turn up?

Given that 32 octet fingerprint is required for the fixed-info and that
fingerprint is onl;y defined for v5 keys it won't be possible to use v4
keys.

In the current draft of openpgp-pqc, it looks like only the algid is required in the fixedinfo:

https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-pqc-02#section-5.2.1" class="section-number selfRef" rel="nofollow">5.2.1. https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-pqc-02#name-fixed-information" class="section-name selfRef" rel="nofollow">Fixed information

For the composite KEM schemes defined in https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-pqc-02#kem-alg-specs" class="auto internal xref" rel="nofollow">Table 1 the following procedure, justified in https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-pqc-02#sec-fixed-info" class="auto internal xref" rel="nofollow">Section 10.4, MUST be used to derive a string to use as binding between the KEK and the communication parties.

//   Input:
//   algID     - the algorithm ID encoded as octet

fixedInfo = algID

https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-pqc-02#section-5.2.1" rel="nofollow">https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-pqc-02#section-5.2.1

Did I misread? Or are you implementing a different scheme?

A