Re: [openpgp] V5 Fingerprint again

[Thijs van Dijk <[e-mail]>]

>
> I think we can go slightly further here for depreciation in implementation
> logic: if a primary key is self signed with a stronger algorithm, a sha1
> signature can be considered a security error. This avoids a downgrade
> scenario and catches misconfigurations but should have little potential for
> false positives.
>

Interesting. How do you envision handling an updated selfsig (e.g. to move
the expiration date forward) with a stronger hash than before?
To me, this seems like the most obvious upgrade path (i.e. a way for users
to force moving to a stronger hash), but when taken literally we've just
retroactively revoked all previous signatures.


> The only scenario I can think of where this heuristic is off, is when the
> sender doesn't create their key themselves and isn't itself capable of
> stronger hashes. Not sure if that ever happens?


One could have a gnuk or yubikey generate the key, and if the user agent
*defaults* to sha1 (regardless of whether or not it can support stronger
hashes) you'll have triggered this scenario.

-Thijs