phc-discussions - Re: [PHC] hash encryption

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Date: Wed, 23 Mar 2016 20:02:31 +0300
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] hash encryption

Thank you all for the suggestions and criticism!

On Wed, Mar 23, 2016 at 02:47:13PM +0100, Dmitry Chestnykh wrote:
> You can use it in SIV-like deterministic encryption mode to avoid nonce collisions and add authentication:
> 
> iv = HMAC(Key, "yescrypt-encryption-IV" || passwordHash || salt)
> encryptedPasswordHash = iv || (PBKDF2(Key, iv) XOR passwordHash)
> 
> To decrypt, generate PBKDF2 stream using the prepended IV, then XOR it with encryptedPasswordHash, generate IV with result and compare it with the attached IV.

A major drawback is that this would require storage of the IVs along
with the hashes.  That's a significant increase in storage requirements.

> On 23 Mar 2016, at 10:47, Dmitry Khovratovich <khovratovich@...il.com> wrote:
> > Simplest scheme would be SHA-256 in the counter mode.
> > 
> > Just XOR SHA-256(Key||Nonce||0..0)||SHA-256(Key||Nonce||0..01) to the block[4], that's it.

This relies on having a nonce, which is something I am trying to avoid.

We do already have salts, which are preferably unique and could be
reused, but as I mentioned before I'd like not to increase reliance on
them being unique.

Alexander