Re: [openpgp] PKI (RFC 5480) mapping to ECC keys (RFC 6637)

Werner Koch <wk@gnupg.org> Sat, 20 July 2013 08:24 UTC

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From: Werner Koch <wk@gnupg.org>
To: Andrey Jivsov <openpgp@brainhub.org>
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Date: Sat, 20 Jul 2013 10:20:02 +0200
In-Reply-To: <51E9A029.6000303@brainhub.org> (Andrey Jivsov's message of "Fri, 19 Jul 2013 13:23:05 -0700")
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Subject: Re: [openpgp] PKI (RFC 5480) mapping to ECC keys (RFC 6637)
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On Fri, 19 Jul 2013 22:23, openpgp@brainhub.org said:

> The simplification is generic. Now that we would have 3 IDs for ECC,
> it is more efficient to check 18 <= x <= 20 then for 3 arbitrary

Compared to the cyrpto operations any efficieny here is a joke.

> Do we know of at least one case when 20 is used in deployed
> applications? This will be enough to require 22 for ECDSA+ECDH.

GnuPG supported this from 1998 to 1.3.5 (2004-02-26).  I have hundreds
of those signatures in my keyrings despite that there is no more support
in GnuPG.  Recycling this identifier would be a Bad Thing™.  Internal
PGP versions used a couple of the lower numbered IDs and they have not
been recycled, either.

> Let me answer why do I think that ECDSA+ECDH ID is a useful feature.

I agree that it is useful; I only remarked that the X.509 based
rationale is a bit weak.

> right now. Assuming that most OpenPGP keys are RSA keys, they use
> sign+encrypt ID 1 and then use the appropriate key usage flags.

Or 2 or 3.  They still pop once once in a while.

> The compact ECC point representation plus ECDSA+ECDH ID in a single
> document is one way to do this.

>From my understanding of the IETF procedures this will indeed be the
case.

> I was wondering, however, that given that ECDSA+ECDH ID is such an
> easy change that fits in a few sentences, it feels like an errata to
> the RFC 6637. All it needs to say is that "use ID 2x for ECDSA+ECDH"
> and then define that ID in another sentence.

Maybe, but recall rfc4880 states:

   initial values for this registry can be found in Section 9.  Adding a
   new public-key algorithm MUST be done through the IETF CONSENSUS
   method, as described in [RFC2434].

That is for an algorithm but not the id, though.  Please use whatever is
the easiest way for you.

I would appreciate if we could informally agree on an identifier right
now so that I can put it into the next GnuPG 1.4 release which is due in
a few days.  This would avoid a '?' as algorithm in a key listing.


Salam-Shalom,

   Werner


-- 
Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.