Nick Galbreath <[email protected]> writes: > Thanks Simon. > > And now that I can read it... ;-) > > * need more detail on salt and format and allowed characters. For > some reason the man page on crypt-256/512 is very specific on the > allowed salt alphabet, etc.
Sure. > * need reference to base64, most likely http://tools.ietf.org/html/rfc3548 > As I learned the hard way there several, and crypt-256/512 uses a > very custom one. RFC 4648 even. :-) > * looking at the name/value pairs, if a single variable, in one order, > case sensitive isn't so bad. However, I'll re-read Solr's other ideas Yeah, I think the N= etc stuff wasn't baked, so other ideas are probably better. > * "where N, r and p are unsigned decimal numbers" this probably needs > more details on allowable ranges and types, e.g. "positive integers" > Copying the spec isn't bad here, but I need to think how this can be > simplified. > > N CPU/Memory cost parameter, must be larger than 1, > > a power of 2 and less than 2^(128 * r / 8). > > r Block size parameter. > > p Parallelization parameter, a positive integer > > less than or equal to ((2^32-1) * hLen) / MFLen > > where hLen is 32 and MFlen is 128 * r. > > * needs something on happens on error if parameters are misformed or > incorrect or out of range. > > * I'd add a references section Yep. > Just made a gitorious account under 'ngalbreath' I'm happy to make > these changes. You have permissions, please go ahead! /Simon > thanks! > > nickg > > > On Tue, Sep 18, 2012 at 11:05 AM, Simon Josefsson <[email protected]> wrote: >> Sorry, the repository was renamed... see here instead: >> >> https://www.gitorious.org/scrypt/scrypt-unix-crypt/blobs/master/unix-scrypt.txt >> >> /Simon >> >> Nick Galbreath <[email protected]> writes: >> >>> 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
