Signer's User ID

Werner Koch <> Thu, 21 July 2005 06:03 UTC

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Subject: Signer's User ID
From: Werner Koch <>
Organisation: g10 Code GmbH
OpenPGP: id=5B0358A2;
Date: Thu, 21 Jul 2005 07:39:32 +0200
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I'd like to have a clarification of the signature subpacket Signer's User ID


    This subpacket allows a keyholder to state which User ID is
    responsible for the signing. Many keyholders use a single key for
    different purposes, such as business communications as well as
    personal communications. This subpacket allows such a keyholder to
    state which of their roles is making a signature.

    This subpacket is not appropriate to use to refer to a User
    Attribute packet.

It is not clear to me whether the string should be a verbatim copy of
the content of a User ID packet or some other information.  The second
paragraph could be viewed as a hint for a verbatim copy.

OTOH, for applications it makes more sense to have just the vanilla
mail address (mailbox@domain) here.  This would make it easier to
compare a mail's From address to the actual signature.

I don't care much about this but given that such a subpacket has been
defined but is not widely used - if at all - we might want to define
it in a stricter way.