Re: [openpgp] Clarify status of subkeys with certification use

[Daniel Kahn Gillmor <[e-mail]>]

On Mon 2018-05-07 20:09:01 +0200, Kristian Fiskerstrand wrote:
> In any case, there have been discussions along the way, so I propose we
> explicitly mark certification subkeys forbidden and ignored by
> implementations.
>
> Maybe something like;
> "when generating a subkey binding signature, the implementation MUST NOT
> set the certify usage flag. When interpreting a subkey binding
> signature, implementations MUST ignore the certify subkey binding usage
> flag if it is set."

I like this proposed text.

> PS! As a tangent point, we likely also want to change the default
> behavior for no usage flag specified for v5 to be ignored as not having
> a recognized flag, instead of defaulting to all features, although I
> don't have a specific proposal for this.

This is a separate point, but it also seems reasonable to me.  I'd be
fine either way -- but we probably still want to specify that v5
implementations making a subkey MUST include a key usage subpacket in
the hashed subpackets section.

    --dkg