Clarification on how revokation works

[David Shaw]

On Wed, Dec 01, 2004 at 04:40:44PM -0700, Chris De Young wrote:
> Hi,
> 
> This is probably a dumb question, but I just want to clarify how key 
> revokation works...
> 
> Am I correct in thinking that really only the public key of a key pair is 
> what is revoked?  (Though the secret key isn't all that useful without the 
> public key being valid, of course.)

Yes.  The secret key at that point is only useful for decrypting
things that were encrypted before the key was revoked.

> We have, in addition to people's individual keys, a shared key used for 
> sending encrypted material to a group of people.  Each member of the group 
> received a copy of the secret key with a temporary passphrase, then 
> (presumably) changed the passphrase to something of their own.
> 
> Any member of the group with the secret key can revoke that key, 
> effectively for everyone - right?

Yes.

> At a basic level, revoking a key is really just a matter of creating a 
> signed statement saying "this key is no longer valid," yes?

Yes.  And note that it's possible (though very difficult in practice)
to unrevoke a key by removing that statement.

I assume you are speaking about revoking a whole key here.  It is also
possible to revoke a subkey and a user ID.

David