phc-discussions - Cryptographically strong salt is not overkill

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Message-ID: <54078A17.1030300@ciphershed.org>
Date: Wed, 03 Sep 2014 17:37:27 -0400
From: Bill Cox <waywardgeek@...hershed.org>
To: discussions@...sword-hashing.net
Subject: Cryptographically strong salt is not overkill

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I just started poking into the Makwa code.  I'm still not sure if I'm
qualified to review it, but I can always comment on code.  I saw the
following comment:

    /*
     * A cryptographically strong PRNG is kinda overkill for a salt,
     * but it does not hurt to use one.
     */

This is not true!

If any salt generator that produces data that is distinguishable from
random data makes it into CipherShed, I will be pretty pissed off.
Don't forget that some users have a valid need to store the salt in
plain-text without letting an attacker know that it is in fact not
just random data.

This is a critical feature for both stenography and plausible
deniability.  Detectable salt would destroy the hidden volume feature
CipheShed inherits from TrueCrypt.

That said, I haven't reviewed the CipherShed code yet like I'm
reviewing this code...

Bill
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