Re: [Cfrg] Adoption of draft-agl-cfrgcurve-00 as a RG document

Dan Brown <dbrown@certicom.com> Tue, 06 January 2015 16:30 UTC

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From: Dan Brown <dbrown@certicom.com>
To: "'alexey.melnikov@isode.com'" <alexey.melnikov@isode.com>, "'cfrg@irtf.org'" <cfrg@irtf.org>
Thread-Topic: [Cfrg] Adoption of draft-agl-cfrgcurve-00 as a RG document
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Date: Tue, 6 Jan 2015 16:28:38 +0000
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Subject: Re: [Cfrg] Adoption of draft-agl-cfrgcurve-00 as a RG document
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> -----Original Message-----
> From: Cfrg [mailto:cfrg-bounces@irtf.org] On Behalf Of Alexey Melnikov
> 
> This message starts 2 weeks adoption call (ending on January 19th 2015)
on:
> 
> https://www.imperialviolet.org/cfrgcurve/cfrgcurve.xml
> 
> as the starting point for the CFRG document which describes an algorithm
for
> safe curve parameter generation for a particular security level and also
> recommends a specific curve (2^255-19) for the 128-bit security level.
> 
> Please reply to this message or directly to CFRG chairs, stating whether
you
> support (or not) adoption of this document. 

[DB] I would definitely support this if the CFRG is open to later (say,
perhaps after a six-month cooling-off period) discussion of some alternative
elliptic curves, such as, a similar set of curves with say random
j-invariant, and perhaps some other security characteristics.

I trust the other CFRG members to have verified that the current proposals
have made improvements over older curves on side channel resistance,
ease-of-implementation, and efficiency (which can also be useful for a
security by boosting the curve size).  So, I think any future curves should
maintain those characteristics: my condition above does not hinge on
revisiting those issues.

I agree that a rigidity-like property does indeed slightly reduce the
security risk compared to an inexplicably-chosen curve.  I'm for
risk-reduction. I think there is room to reduce the security risk further
(or at least in a different direction), compared to the rigid-type curves,
hence the condition on my support.  I am not too worried on the details of
how rigidity is achieved, since it is rather small thing compared to
resisting known attacks (e.g. side channels, error-prone complexity), and
compared to what I think are the more realistic risks, or at least possibly
better risk-reduction methods. So, if the current logjam in CFRG consensus
is only about which rigidity-like properties to prefer, with the effect that
the other more substantial security improvements are being delayed, then I
support the chairs pushing ahead.  That leaves a small risk between flavours
of rigidity, but I see that small risk as worth the other substantial
security gains, especially if we are open to revisiting risk-reduction in
the future.

Best regards,

Dan