phc-discussions - Re: Password hashing as a self-overwriting Turing machine

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Message-ID: <20150701175549.1c001a68@lambda>
Date: Wed, 1 Jul 2015 17:55:49 +0000
From: Brandon Enright <bmenrigh@...ndonenright.net>
To: Marsh Ray <maray@...rosoft.com>
Cc: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>,
 bmenrigh@...ndonenright.net
Subject: Re: Password hashing as a self-overwriting Turing machine

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On Wed, 1 Jul 2015 17:48:31 +0000
Marsh Ray <maray@...rosoft.com> wrote:

> Perhaps I misread, thinking of your description of a Turing machine
> which uses data-dependent addressing. If memory addresses are fixed
> in advance only by the salt, is it so easy to prove the resulting
> system is Turing complete?
> 
> 
> -           Marsh


I don't see the problem.  The if the salt is the seed to some
pseudo-random function then you can think of the salt as the program.
Under basic assumptions about the prf (random oracle) there exists some
stream of instructions that can do arbitrary computation.

Actually finding a salt that produces this "useful" stream of
instructions seems irrelevant.

Brandon

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