Re: [Cfrg] EC signature: next steps

Rene Struik <rstruik.ext@gmail.com> Fri, 04 September 2015 13:24 UTC

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To: Alexey Melnikov <alexey.melnikov@isode.com>, "cfrg@irtf.org" <cfrg@irtf.org>
References: <55DD906F.3050607@isode.com> <D2035132.531EE%kenny.paterson@rhul.ac.uk> <55DDA21D.9060302@isode.com> <55DF3E3C.7020206@isode.com> <55E42414.3020805@isode.com>
From: Rene Struik <rstruik.ext@gmail.com>
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Date: Fri, 4 Sep 2015 09:24:12 -0400
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Subject: Re: [Cfrg] EC signature: next steps
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Dear colleagues:

I think the signature scheme should facilitate the following:
a) signature generation.
Ideally, signing should be possible without requiring the signer to 
access its public key (obviously, it does require the private key). For 
Schnorr and ECDSA type schemes, one does not need to include the public 
key in the signing process, since security in the multi-user setting is 
roughly the same as in the single-user setting (see [1], [2]).
b) signature verification.
If the public key of the signer is not included with signing, it is also 
generally not required with verification (if the signature includes the 
ephemeral signing key), since then the public key of the signer can be 
reconstructed from the signature itself (with Schnorr signature (R,s) 
over message m, one has Q=(1/h)(R-sG), where h=H(R,m)). This may have 
advantages in settings with certificate chains and with single 
signatures (where one can reduce overhead to identify the public key of 
the signer).
c) reuse of same signing key with IUF/non-IUF schemes.
Ideally, one should be able to use the same signing key, no matter 
whether one uses the signature scheme in the so-called IUF setting or in 
the non-IUF setting. If I understand correctly, consensus is to only 
specify an IUF-scheme, but even then, the design should be so that it 
can support both flavors. This should *not* be left to applications to 
specify (and can also easily be done).
d) same signature scheme for Weierstrass curves, (twisted) Edwards 
curves, and Montgomery curves.
The signature scheme should work for all these three schemes and not 
just for (twisted) Edwards curves. Ideally, it should also work for Huff 
curves, Jacobian curves, etc., without requiring any changes outside the 
scalar multiplication routine.

Best regards, Rene

Ref:
[1] A. Menezes, N.P. Smart, "Security of Signature Schemes in A 
Multi-User Setting", CACR-Corr-2001-063.
[2] J. Malone Lee, S. Galbraith, N. P. Smart, "Public Key Signatures in 
the Multi-User Setting", Inform.Proc.Letters, 2002.




On 8/31/2015 5:53 AM, Alexey Melnikov wrote:
> Dear CFRG participants,
>
> Many thanks to Ilari for posting this updated summary of where things
> currently stand. Kenny and I would now like to run a short discussion
> focusing on this summary, with our intention being to flush out any last
> issues or additional points of comparison between the different schemes
> that everyone should be aware of.
>
> Once everyone has kicked the tires, so to speak, we plan to move to a
> poll to decide which scheme CFRG should focus on writing up and formally
> recommending. We, as chairs, are hoping these steps will get us to the
> finishing line.
>
> So:
>
> - are there important characteristics or points of comparison that
> Ilari's summary does not cover?
>
> - are there errors of fact or omission that need to be corrected?
>
> - anything else?
>
>
> We'll let this discussion run for exactly one week, but we might extend
> the time if the discussion is still going strong and new arguments or
> points of comparison are brought up. After that, if no major new
> information is brought up, we will start the Quaker poll for selecting a
> single CFRG-recommended signature scheme.
>
>
> Best Regards,
> Kenny and Alexey
>
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