phc-discussions - Re: [PHC] Specification of a modular crypt format

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Message-ID: <CAGiyFdfeWg9E00syMJEPTKup5u0JiKHpbax1bhhejAOBO3L0eQ@mail.gmail.com>
Date: Thu, 08 Oct 2015 09:22:17 +0000
From: Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Specification of a modular crypt format

Do you think the specs/code at https://github.com/P-H-C/
1) cannot be finalized as they are and require major changes
2) could use some optimization but are acceptable as they are
3) are perfectly fine
?


On Thu, Oct 8, 2015 at 12:38 AM Solar Designer <solar@...nwall.com> wrote:

> On Sat, Sep 19, 2015 at 07:02:51PM +0200, Thomas Pornin wrote:
> > The code includes some generic Base64 encoder/decoder (about 150 lines),
> > then code specific to Argon2i (about 200 lines), and some test vectors.
> > The Base64 code is constant-time with regards to the data contents (no
> > data-dependent table lookups or branches); this is probably useless in
> > most situations, but easy enough to achieve.
>
> It is in fact (at least theoretically) desirable to have salt decoding
> cache-timing-safe when (or just in case) the hashing scheme itself is
> not cache-timing-safe or/and the hash comparison is not timing-safe.
>
> This also means that en/decoding the salt, instead of using it verbatim,
> results in extra risk.  Yet we seem to have chosen to do that to provide
> a more generic interface to the underlying hashing scheme.  (I did post
> this sort of rationale in here.  I should have mentioned the above
> drawback in that same message.)
>
> While we probably can implement things safely ourselves, third-party
> implementations are a (bigger) concern.
>
> Alexander
>

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