phc-discussions - Re: [PHC] What is "basic cryptography" ?

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Date: Tue, 14 Oct 2014 13:26:48 +0200
From: Krisztián Pintér <pinterkr@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] What is "basic cryptography" ?

On Tue, Oct 14, 2014 at 11:50 AM, Dmitry Khovratovich
<khovratovich@...il.com> wrote:
> Just do not store the
> inputs to the first call of the Mix operation  in memory and store only the outputs. This does not
> allow to recover the password from any portion of memory

it is unfeasible but theoretically possible. this is the same
conversation we had about side channel resistance. consider a cold
boot attack, or any other memory recovery attack *without* having the
password hash. if the RAM intensive intermediate data is blinded, it
helps the attacker in no way. if it is not blinded, now he has a
verification method. if the captured memory is from the later stages
of the algorithm, it will do exactly as much as having the hash. if
from some earlier stages, it helps that much more. if the password is
weak, or partially known, it is a break.

i'm not totally crazy, let me note. i understand that we have much
more important attack scenarios to deal with. but worth keeping in
mind that storing the password might present some more exposure to
side channels, but keeping megabytes of intermediate data around
presents a whole lot more increase in said exposure. for what it's
worth.