Re: [openpgp] To bind or not to bind

[Justus Winter <[e-mail]>]

Hi Falko :)

Falko Strenzke <[e-mail]> writes:

> Am 25.03.24 um 11:21 schrieb Justus Winter:
>>> Based on what you write and what I can see in PGPy's GitHub repository,
>>> it seems PGPy has to be considered as unmaintained. In that case it
>>> should not be considered in the interop tests.
>> We're trying to understand how the existing v4 ecosystem will react to
>> introducing an as-of-yet unknown algorithms with as-of-yet unseen
>> artifact encodings to v4 certificates.
>>
>> Whether or not an implementation is actively maintained seems to be
>> irrelevant to that question.
>>
>> Or, one could even argue that not inadvertently breaking unmaintained
>> implementations is more important.  Along those lines, Aron has been
>> arguing that gopenpgp reacting badly to unknown algorithms isn't that
>> bad because gopenpgp is actively maintained.
>
> But here we are weighing the two possibilities
>
> 1) introduce PQC encryption already in v4
> 2) introduce PQC encryption only in v6.
>
> PGPy being unmaintained will block either route. So I don't see that the 
> failing interop test is an argument for for 2).

It is true that if I create a new v4 key and add a PQC encryption subkey
to it, it will not work with current versions of PGPy (or GopenPGPv2),
and that is true also if I create a new v6 key (with or without PQC
encryption subkey).

But, I could also add a PQC encryption subkey to my *existing* v4 key.
In this case, I think it is not unreasonable to expect it to continue to
work with PGPy (or GopenPGPv2), but it does not.  Worse, when a user
discovers this, it is hard to impossible to undo this mistake: revoking
the PQC encryption subkey (likely, I haven't checked) does not help, and
manually stripping the PQC encryption subkey and binding signature may
help, but can be undone at any point by any kind of cert
synchronization.

Therefore, I believe that allowing PQC encryption subkeys being added to
v4 keys is a giant footgun that inflicts irreparable damage to peoples
existing v4 keys.

Best,
Justus