Re: [Cfrg] Recommending secp256k1 in FIPS 186-5

Neil Madden <neil.e.madden@gmail.com> Thu, 19 December 2019 19:10 UTC

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From: Neil Madden <neil.e.madden@gmail.com>
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Date: Thu, 19 Dec 2019 19:10:26 +0000
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To: Tony Arcieri <bascule@gmail.com>
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Subject: Re: [Cfrg] Recommending secp256k1 in FIPS 186-5
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>> On 19 Dec 2019, at 18:02, Tony Arcieri <bascule@gmail.com> wrote:
> 
>> On Thu, Dec 19, 2019 at 9:56 AM Neil Madden <neil.e.madden@gmail.com> wrote:
> 
>> But see https://datatracker.ietf.org/doc/draft-ietf-cose-webauthn-algorithms/ ...
> 
> 
> I can't say I think too highly of a draft dated November 1st, 2019 which is recommending only RSASSA PKCS#1v1.5 and ECDSA w\ secp256k1.
> 
> Especially in the case of the former this seems unwise given the lingering history of BB'06 (which continues to cause real-world breakages... there was a BlackHat talk about it this year)

Indeed. As I understand it that draft is registering algorithm identifiers already in use by WebAuthn/FIDO (TPM attestation I believe) and the RSA ones are all explicitly marked as non-recommended or immediately deprecated.

However, secp256k1 *is* currently marked as recommended in that draft. For signature use only; I managed to get explicitly wording added not recommending it for ECIES/“ECDH-ES” encryption, but I’m not aware of any specific weakness for ECDSA use so I didn’t argue against it for that. If there are concerns for signature use then it’d be good to raise them with the COSE WG now. 

(I had a brief look at that draft when it was brought to my attention as it also registers JOSE algorithms, which might impact my employer. I’ve not followed either that draft or the COSE WG very much since so I don’t know much about it beyond what is in the draft itself).

— Neil