Re: [Cfrg] I-D Action: draft-irtf-cfrg-argon2-10.txt

Stephen Farrell <stephen.farrell@cs.tcd.ie> Thu, 09 April 2020 11:22 UTC

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To: Milan Broz <gmazyland@gmail.com>, cfrg@ietf.org
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Thu, 9 Apr 2020 12:22:14 +0100
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Subject: Re: [Cfrg] I-D Action: draft-irtf-cfrg-argon2-10.txt
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Hiya,

On 09/04/2020 10:05, Milan Broz wrote:
> On 07/04/2020 01:41, Stephen Farrell wrote:
>>
>> Hiya,
>>
>> I did an IRSG review for -09. This addresses all the issues
>> that I found there, except one, and that being (I think)
>> the most important one;-)
>>
>> The issue: What is a "primary variant" and what is an
>> implementer supposed to do?
>>
>> The above is a quote from my review of -09. Apologies if I
>> missed some change in -10 that addresses this.
>>
>> Let me make a suggestion: state that argon2id is mandatory
>> to implement, and that the other variants are not.
> 
> Hi,
> 
> Argon2id is combination of Argon2i + Argon2d, so implementing
> all three variants should be quite easy (code must be there anyway,
> it is just about providing external interface to it).
> 
> I think all variants should be mandatory...  and as I understand
> the current RFC draft (3.1 section), it already says so:
> 
> o  Type y of Argon2: MUST be 0 for Argon2d, 1 for Argon2i, 2 for
>       Argon2id.
> 
> (We use Argon2 in cryptsetup/LUKS2 and Argon2i (not id) is
> currently the primary variant for the key derivation.
> For compatibility with existing devices we need support
> for all three variants. But obviously, this is just one use case,
> RFC is more generic.)

I'd also be fine with all being mandatory to implement
but would prefer just one. Even if there's not much cost,
in terms of code, there would be follow on cost in terms
of assigning code-points at higher layers, and in terms
of the arguments that will ensue about which code-point
to use/assign in various contexts. Providing more options
at this level is usually a bad plan that's unfortunately
attractive to many cryptographers;-)

But my main ask is just that it be clear what's expected
of an implementer, so we get better interop.

S.

> 
> Thanks,
> Milan
>