Allowing import of pubkeys without User ID

[Andrew Gallagher]

On 12 Jan 2023, at 08:33, Werner Koch via Gnupg-devel <gnupg-devel at gnupg.org> wrote:
> 
>   - Zero or more Subkey packets
> @@ -4106,7 +4106,7 @@ may have more than one email address, and construct a User ID for each
> one.  A transferable public key SHOULD include at least one User ID
> packet unless storage requirements prohibit this.
> 

There is another use case, not previously discussed IIRC, where distributing a TPK without any User ID is desirable. In order to implement RTBF, keyservers must be able to remove personal information from their databases. If a key owner wishes their personal information to be deleted, but this information is attached to a revoked primary key, then removing the entire key from the keyserver will also remove the revocation, which opens a security loophole.

It should be possible to still serve the revocation to those people who already have a copy of the full key, without serving the associated personal information to those who do not. Bare revocations may not be sufficent, as these will only be searchable via the primary key fingerprint, whereas keys are often searched for by a subkey fingerprint (e.g. to validate sigs).

HIP 5 [1] is an attempt to implement a distributable RTBF declaration using direct revocations, however it requires UID-less TPKs, and may also require multiple direct revocations to be distributed (e.g. a key may be RTBFed *and* compromised). This cannot (IMO) be reliably done using only UIDful TPKs or bare revocations.

A

[1] https://github.com/hockeypuck/hockeypuck/wiki/HIP-5:-Reliable-personal-data-deletion-using-self-signatures

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