Re: [openpgp] Combining signature with signer's public key

["Neal H. Walfield" <[e-mail]>]

On Fri, 11 Dec 2020 10:01:49 +0100,
Wiktor Kwapisiewicz wrote:
> On 11.12.2020 09:34, Neal H. Walfield wrote:
> > One thing to be aware of: the subpacket areas can only hold 64kb of
> > data.  So, you really should minimize the certificate.
> 
> Minimizing the certificate is actually a good idea regardless of the
> certificate transport method (Autocrypt header, signature subpacket,
> notation etc.).

I agree that when we need to optimize for space, data whose utility in
the particular context is zero or less should be stripped.

> It would be good to specify what actually would that minimized cert
> contain. I think the primary key + valid encryption subkey + signing
> key that signed the e-mail + User ID of the sender which contains
> their e-mail address (or the primary one if there is no better match)
> would constitute the minimal set. Of course clients on the receiving
> side should properly merge the cert with what they already have (*not*
> replace it).

I think over specifying is bad, because what is useful is context
dependent.  Should I be forbidden from including third-party
certificates?  What if I suspect that one of them would allow you to
authenticate my certificate?  What if I have per-device encryption
subkeys and I know that your implementation will encrypt to them all,
like Open Keychain?  Do I have to choose one?

:) Neal