On Tue, Sep 18, 2012 at 08:51:06AM +0200, Simon Josefsson wrote: > We could start it as a parallel effort though. Would you like to help > work on this? I started a document here: > > https://www.gitorious.org/scrypt/scrypt/blobs/master/unix-scrypt.txt
FWIW, I am planning to do some research/testing/benchmarking of scrypt for this kind of uses very soon. Chances are that I'll want to make modifications to scrypt proper as a result - probably at least have an optional time-memory tradeoff defeater (a fourth parameter) as briefly discussed with Colin on the crypt-dev list. Naturally, I expect some healthy resistance to any proposed modifications to scrypt, now that it's been around for 3 years and is about to get standardized. Yet I think this is something to discuss and consider. There are also some difficulties with using scrypt as a crypt(3) password hash type. As discussed on crypt-dev, scrypt at <= 1 MB (yes, misuse of it) is not a good replacement for bcrypt, whereas scrypt at much larger memory settings (proper use) should better be used with concurrency limits (not currently found inside crypt(3) implementations, nor in many crypt(3)-using daemons). So the issue is a bit non-trivial. Speaking of the encoding syntax, I think the key=value,... style of syntax is probably a bad idea. It complicates parsing and brings up unnecessary questions such as whether a parser is supposed to handle keys in the one standard order only or in any order, etc. IIRC, the "rounds=..." thing first appeared in SunMD5, then was reused for SHA-crypt, and well, there were some parsing ambiguities with them. It might be better to just allocate a fixed number of base-64 characters at the start of the string (right after the $7$ or whatever hash type prefix) to correspond to the parameters. And if we need to add an extra parameter later, we just pick a new prefix (call it e.g. $7a$). I used a similar approach in phpass "portable hashes", where the character right after the $P$ prefix holds base-2 logarithm of the iteration count. This is trivial to parse and encode, and there's just one valid encoding. So I suggest that we try not to make things more flexible than we actually need them to be. Thanks, Alexander
