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Re: [openpgp] From the DT: v5 certificates put certificate-wide and primary-key-specific subpackets in direct key sig on primary key

2022-05-04 06:24:18
Thanks dkg,

Just one point of clarification regarding:

As a result of this set of changes, an OpenPGP v5 certificate MUST have
a direct-key self-signature if it wants to indicate any of these
preferences.

In the current editor's draft, the direct-key signature is required for
v5 keys even if it doesn't care about any of the preferences [0].
(Though I expect that almost all keys will want to specify at least the
Key Flags and Features subpackets, so that should be uncommon anyway.)

The reason it's required is that if you generate a key with an
expiration time, for example (specified in the direct-key signature),
the expiration time cannot be removed without access to the private key
(as simply removing the direct-key signature renders the key unusable).

This is similar to certain implementations requiring a User ID binding
signature for v4 keys, even though the specification never required
those. Instead, the editor's draft says that for v5 keys, the User ID
binding signature should not be required (since direct-key signatures
now serve this purpose), which has advantages when distributing keys
for anonymous, catch-all or unverified email addresses.

Of course, feedback about this is welcome too.

Best,
Daniel

[0]: https://openpgp-wg.gitlab.io/rfc4880bis/#section-5.2.3.7-9

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