Subkey revocation signature

[David Shaw]

On Feb 4, 2014, at 6:53 AM, Thomas Oberndörfer <info at mailvelope.com> wrote:

> Hello,
> 
> I'm trying to verify subkey revocation signatures created with GPG.
> 
> RFC4880 says:
> "Key revocation signatures (types 0x20 and 0x28) hash only the key
> being revoked"
> http://tools.ietf.org/html/rfc4880#section-5.2.4
> 
> But when I compute the hash data only with the subkey packet the
> verification fails.
> 
> I then tried to hash primary and subkey packet together and the
> verification succeeded.
> 
> So it looks like GPG is calculating subkey revocation signature
> (type 0x28) in the same way as the binding signature (type 0x18).
> 
> Is this correct? And if yes is this not a deviation from RFC4880?
> I'm currently implementing this verification in OpenPGP.js and
> not sure how to handle this case.

This is correct - a subkey revocation hashes both the primary and subkeys, similar to a binding signature.  The language in 4880 was in error, and an errata was filed for it: http://www.rfc-editor.org/errata_search.php?rfc=4880&eid=3298

David