https://www.gitorious.org/scrypt/scrypt/blobs/master/unix-scrypt.txt
has vanished! (or I get a 404) On Tue, Sep 18, 2012 at 5:10 AM, Simon Josefsson <[email protected]> wrote: > Solar Designer <[email protected]> writes: > >> 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. > > Yes selecting parameters is difficult. I'm also concerned that too > small parameters end up being weaker than PBKDF2/bcrypt. Generally, I'm > not entirely sure how one would use scrypt for authentication services > -- probably the best is to reserve a chunk of memory and setup a scrypt > computation service. You would then have no issues up until some > pre-determined number of authentications/second, that you could > rate-limit per-user on. > >> 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. > > Excellent, this was the kind of feedback I was hoping for. I agree. If > you have a gitorious account and want to help with the document, I'll > add you. > > /Simon
