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From: Jon Callas <jon@callas.org>
In-Reply-To: <513899DF.60109@fifthhorseman.net>
Date: Thu, 7 Mar 2013 10:59:20 -0800
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To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
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Cc: IETF OpenPGP <openpgp@ietf.org>, Jon Callas <jon@callas.org>
Subject: Re: [openpgp] marking subkeys as constrained for specific use -- new
 key usage flags?
Precedence: list

On Mar 7, 2013, at 5:45 AM, Daniel Kahn Gillmor <dkg@fifthhorseman.net> =
wrote:

>=20
> If criticality is fraught with problems, doesn't that suggest =
extending
> the usage flags is a more responsible way to go?

No, because either you want *that* to be critical, too, which has the =
same criticality issue, or criticality is not important in which case =
the notation works too.

My comment was one about criticality in general. We have criticality =
because there were people in the late '90s who thought it was a good =
idea. It *is* a good idea, but it is such a subtle idea that it's =
Shannon information, kolmogorov complexity, etc. is more than one bit.

>=20
> or should i create a subkey with all usage flags set to 0, and then
> include a notation to indicate the use?  that way, the subkey wouldn't
> be used by any existing system except the ones willing to parse and
> interpret the notation, regardless of its criticality.

Well, if you did that, you wouldn't not be RFC 4880 compliant. There is =
a way to do this within the standard -- the notation.

The whole reason that we have notations is so that if you want to do =
something on your own, there's a supported way to do that. What's wrong =
with using the supported way, as opposed to violating the standard with =
hacks? (I'm not above violating standards with hacks, but I expect to =
have to answer that question, myself.)

If my cynical beliefs about criticality scared you away from doing the =
right thing, then I apologize. I never intended to do that. I was merely =
pointing out that if you put the critical flag on it, then it possibly =
would have unintended failure modes and meta-failures.

The correct thing to do is a notation. Put the critical flag on it. =
Please.

	Jon