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Message-ID: <20160324143456.GA10719@openwall.com> Date: Thu, 24 Mar 2016 17:34:56 +0300 From: Solar Designer <solar@...nwall.com> To: discussions@...sword-hashing.net Subject: Re: [PHC] hash encryption On Thu, Mar 24, 2016 at 03:29:34PM +0300, Solar Designer wrote: > I am considering hashing in round+keylen. No, this does not fully do the trick, and is unnecessarily complex to reason about. > Another detail is that 6 least significant bits of keylen don't really > need to be encoded, but this detail doesn't appear to be of any use, > unless we were to encode (round + (keylen >> 6)) and declare keylen's > needing more than 14 bits unsupported. This isn't exactly right. It would need to be "number of SHA-256 blocks" instead of just "keylen >> 6". This gets too complex. So not wanting to double the SHA-256 block count for keylen=32 and not wanting to introduce too much complexity (to code or/and reasoning), we seem to be limited to either relying on the trick I suggested earlier (hash in the round number last) or providing a mitigation only for keylen up to 2^24 (if we use aligned 32-bit words only) or up to 2^48 (if unaligned, fully using space up to the max of 55 bytes). Alexander
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