phc-discussions - Re: [PHC] Argon2 improvement thread

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Message-ID: <CA+hr98H1PMaAygo7jcQ67Vjnd6gDuBP7pY-HAYbyhr1coChbeg@mail.gmail.com>
Date: Thu, 13 Aug 2015 15:30:58 +0200
From: Krisztián Pintér <pinterkr@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] Argon2 improvement thread

i proposed earlier to leave any such maintenance task to an outer
layer. i'm not even sure it needs standardization at all, especially
not within the scope of PHC.

in particular:

1, i propose not doing allocation within the hash function at all.
memory should be void* parameter to a buffer to use. rationale: there
are different ways of allocating memory. on embedded systems, there
might be no heap at all, and there might be different kinds of memory
(internal, external, etc). only the caller knows how to allocate and
then properly clean a memory block.

2, i propose taking the password and the salt in a pre-padded, fixed
size block. rationale: it might be not straightforward how to copy the
password from a buffer in a manner that does not leak the password
length. if the password is hashed, hashing leaks length like nothing
else. padding is of utmost importance.

3, there is no need to implement a separate verify interface.
rationale: verification is supposed to be a timing-safe comparison,
and can be or already is provided by other libs.

4, if the algorithm provides server relief, the interface should
reflect to that, and have two parts, pass 1 and pass 2, which are
supposed to be chained together when server relief is not used.
rationale: usage modes belong to the outer layers, the core should be
as simple as possible (but not simpler). there is no need for a
function that combines the functionality of other two functions.

5, the result should be a binary of the designed length. no encoding
or parameter-prepending is necassary. rationale: it is the task of the
outer layers. it might be unnecessary to store the parameters at all,
as they might be fixed. an implementor might be short on storage, or
must put the hash in 16 bytes space for back-compat.

i personally don't care too much about any additional optional
interfaces, as long as the core, as explained here, is exposed.

On Thu, Aug 13, 2015 at 3:08 PM, Dmitry Khovratovich
<khovratovich@...il.com> wrote:
> I would rather enable scrubbing in the extended API to simplify the default
> one. The extended API can then have a boolean flag to clean all the inputs
> immediately after they are used.
>
> Maybe there are other opinions on that? So far only a few people
> participated the API discussion...