Re: [Cfrg] [saag] Recommendations Regarding Deterministic Signatures

Benjamin Kaduk <kaduk@mit.edu> Thu, 28 November 2019 19:38 UTC

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Date: Thu, 28 Nov 2019 11:38:01 -0800
From: Benjamin Kaduk <kaduk@mit.edu>
To: John Mattsson <john.mattsson=40ericsson.com@dmarc.ietf.org>
Cc: "cfrg@irtf.org" <cfrg@irtf.org>, "saag@ietf.org" <saag@ietf.org>
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Subject: Re: [Cfrg] [saag] Recommendations Regarding Deterministic Signatures
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On Wed, Nov 27, 2019 at 11:13:55AM +0000, John Mattsson wrote:
> IRTF/IETF has the last years heavily promoted purely deterministic signatures:
> 
>   RFC 8152 (EdDSA):
>     "EdDSA signatures are deterministic."
> 
>   RFC 8152 and RFC8152bis (COSE): 
>     "Implementations SHOULD use a deterministic version of ECDSA"
> 
>     "Note: Use of a deterministic signature technique is a good idea
>      even when good random number generation exists."
> 
>   RFC 8446 (TLS 1.3)
>     "It is RECOMMENDED that implementations implement "deterministic ECDSA""
> 
> NIST has just released FIPS 186-5 (Draft) where they plan to include deterministic ECDSA but does not recommend it in general due to side-channel and fault injection attacks:

Can anyone comment on the relative weight that NIST gives to hardware vs.
software-only implementations?  My understanding is that these attacks can
be quite severe for hardware implementations.

> My current view is that best practice seems to be to use deterministic algorithms (deterministic ECDSA or EdDSA) with "additional randomness" / "noise" like in XEdDSA. This also mitigates attacks on theoretical use cases where deterministically signing the same message twice leaks information.
> 

This does seem like an attractive proposition on first inspection.

Thanks,

Ben