ietf-openpgp
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Re: [openpgp] email death certificates

2019-08-24 22:53:20
On Aug 23, 2019, at 8:03 PM, Michael Richardson 
<mcr+ietf(_at_)sandelman(_dot_)ca> wrote:


David Shaw <dshaw(_at_)jabberwocky(_dot_)com> wrote:
Has anyone given any thought to this?

I suppose it might also apply to "does not work here anymore"

There is a "Reason for Revocation" subpacket for the revocation
signature.  It contains both a machine-readable byte giving various
reasons for revocation (key superseded, compromised, or retired, user
ID no longer valid, or a general "other"), followed by a human-readable
string.

I suppose a death notification would be "key retired", with additional
information (if any) given in the human-readable string.  This works
with the designated revoker feature as well as the regular (self)
revocation, so even if the private key is missing (or, being dead, the
owner is unable to enter a passphrase) the key can still be revoked.

The designated revoker is singular.

There is no k-of-n (or rather K) threshold the way that signature on UIDs
works.  If there was N signatures binding me(_at_)example(_dot_)com to key 
0x12345678,
then it would be nice if the self-sign on the key could set a value k,
which if at least K entities revoke their signature (not just expire) with
an identical reason, would signal that the key<->UID is no longer valid.

Designated revoker is not quite singular.  You can have more than one 
designated revoker on a given key - it is true, though, that any single one of 
them can revoke the key.

I'd be somewhat afraid to use a scheme where people not chosen by me could 
"gang up" and cause a UID to be revoked.  Or for that matter, a single angry 
person could make N keys, sign the UID and then revoke that signature with each 
of those N keys.

Designated revoker lets me, as the key owner, pick who is allowed to kill my 
key.

David

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