phc-discussions - Re: [PHC] POMELO fails the dieharder tests

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Date: Sat, 5 Apr 2014 11:40:41 -0400
From: Bill Cox <waywardgeek@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] POMELO fails the dieharder tests

On Sat, Apr 5, 2014 at 8:37 AM, Peter Maxwell <peter@...icient.co.uk> wrote:
> On 5 April 2014 07:15, Daniel Franke <dfoxfranke@...il.com> wrote:
>>
>> POMELO is one of a handful of PHC candidates which are not constructed
>> around any established cryptographic hash function or cipher. POMELO's
>> security claims include collision-resistance. Unfortunately, its output
>> fails the dieharder tests.
>>
>
> While I don't have the time myself to do it this weekend, it might be better
> actually looking at the PHS output and what's going on in the reference
> implementation because you'd expect at least a wee bit of non-zero results.
> What you've got looks like a bug somewhere.

Looking at the output is a fine idea.  However, I feel very strongly
that computational verification is important.  What Daniel is doing
needs to be done.

> Also, although it's probably not what's causing your results here, I'm
> fairly sure that the dieharder tests aren't great for short inputs.

He ran it in a mode where pomelo is called repeatedly, generating what
should look like an infinite source of random data.  He did it the
right way, and I see no bug in his code.

> If you want to demonstrate an algorithm isn't collision resistant, a sample
> collision usually persuades people, e.g. x = f(a_1) = f(a_2).  Or at least
> provide an argument of how much work would be required to generate a
> collision.

Another way is to have others verify the work.  I just wrote a
completely independent wrapper for pomelo, and verified Daniel's
result.  If anyone's interested, I can throw my git repo for all the
PHC entries up on github.

I'm trying to figure out what the problems are in PAMELO.  The first
one is simple.  There's a bug on line 47:

    // load salt into S
    for (i = 0; i < saltlen; i++)   ((unsigned char*)S)[i] =
((unsigned char*)salt)[i];

It should read:

    // load salt into S
    for (i = inlen; i < saltlen; i++)   ((unsigned char*)S)[i] =
((unsigned char*)salt)[i];

The salt is overwriting the password.  I fixed that in my version, but
the output is still massively non-random.  I printed the output for
several passwords in dieharder format, and found that output values
get repeated a ton.  There's at least one more bug in there.

Bill