Subject: Re: How do I do this with OpenPGP?

From: "Hal Finney" <[email-masked]>
Date: Tue, 7 May 2002 14:56:25 -0700

You should use the signature expiration time subpacket, in Trent's
signature on the key.

Hal

> From: John Dlugosz
>
> One of the nice things about OpenPGP is that multiple signatories are
> possible on a key, each "meaning" something.  Basically, it trent signs a
> key, it's OK with me for (purpose A), and the fact that Carl signed it too
> for some other purpose is beside the point.
>
> But, I want Trent to be able to certify a key for a certain time period.
> Tag 2, type 0x10-0x13 doesn't contain a date.  I suppose there's a more
> complicated way to do this, though?  type 0x1F says "...for statements that
> non-self certifiers want to make about the key itself" so maybe something
> in there?  Or certifing one of the (time range) subkeys instead of the main
> key?
>
> Anyone?

---

From: [email-masked]
Date: Tue, 7 May 2002 17:16:26 -0500

From: John Dlugosz

Thanks, Hal.

Is Trent's signature on the key itself or on a UserID?

It seems that either has semantic implications, but what do existing
general-purpose tools do?  I like the latter for my application.

What's the relationship between the "Trust signature" key subpacket, and
using key types 0x11-0x13?

--John

"Hal Finney" <[email-masked]> on 05-07-2002 04:56:25 PM

To:    [email-masked], [email-masked]
cc:
Subject:    Re: How do I do this with OpenPGP?

Hal

---

From: "Hal Finney" <[email-masked]>
Date: Tue, 7 May 2002 15:13:13 -0700

> general-purpose tools do?  I like the latter for my application.

Normally it is on a userid.  It is binding the given name to the key,
that is, the signature is asserting its belief that the name belongs
to the key and vice versa.

> using key types 0x11-0x13?

The trust signature subpacket is used for the signer to publicly declare
that he trusts the key being signed as a signing key.  Normally a
signature just means that the signer is asserting that the name belongs
with the key, and that's what the signature types 0x11-0x13 are for.

Trust signatures are used to enable what we call "meta introducers"
which are signers who are empowered to declare that other keys have
key-signing authority.  For example, in a corporate application the chief
security officer may be declared to be a meta-introducer by the employees,
and he can then delegate signing authority to departmental officers.

It's a somewhat complicated concept and not usually very useful outside
of relatively closed systems.

Hal

---

From: [email-masked]
Date: Wed, 8 May 2002 10:08:43 -0500

From: John Dlugosz

Thanks again, Hal, the light is beining to dawn.

I'm working on a closed system.  What you describe is pretty much what I'm
doing.

Basically, instead of just "this is Bob" chaining down the trust, with the
assumption that everyone in that chain of trust is within the organization,
I can verify that everything in the chain back to Trent has the trust
signature packet too, meaning that this link is not just some random
employee but someone empowered to say "this is Bob".  Is that right?

So, if I understand right, Trent will put the trust signature subpacket
onto his certification of his vice-trents.  There might be several layers
here, and finally the supervisors who have face-to-face contact with
someone can sign the UserID, but can't further delegate their signing
authority.  The "level" (depth) lets me do that, and the "amount" isn't
useful for my purpose.

--John