phc-discussions - hash encryption

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Message-ID: <20160323034125.GA2904@openwall.com>
Date: Wed, 23 Mar 2016 06:41:25 +0300
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: hash encryption

Hi,

I am planning to release yescrypt 1.0 later this year.  One planned
feature that stayed on my to-do list so far is builtin support for
(re-)encryption of hashes.

One way to do it would be to use a block cipher like AES.  However,
yescrypt does not normally use any block cipher, and bringing in an
extra crypto primitive just for this one feature is not great.

Another way would be to reuse the salt as IV when reusing an already
available hash function as a stream cipher.  However, this increases
reliance on salts being unique.

Yet another way would be to create a block cipher out of a hash, using
the Luby-Rackoff construction.  This is my current preference.

Attached is an implementation of a 256-bit block cipher based on
SHA-256 (which yescrypt has anyway).  I'd appreciate a review.

Thanks,

Alexander

View attachment "sim-encrypt.c" of type "text/x-c" (1515 bytes)