Date: Thu, 26 Jul 2012 03:09:43 +0400 From: Alexander Cherepanov <cherepan@...me.ru> To: john-dev@...ts.openwall.com Subject: Re: mscash2 / hmac-md5 ambiguity On 2012-07-24 03:57, magnum wrote: > On 2012-07-23 23:19, Alexander Cherepanov wrote: >> On 2012-07-23 14:46, magnum wrote: >>> On 2012-07-23 11:47, Alexander Cherepanov wrote: >>>> mscash2 hashes in their canonical form are nevertheless accepted as >>>> hmac-md5: >>>> >>>> $ cat mscash2.john >>>> chatelain:$DCC2$10240#chatelain#e4e15fdfafc8e715da9edec3611bfbff >>>> $ john mscash2.john >>>> Warning: detected hash type "mscash2", but the string is also recognized >>>> as "hmac-md5" >>>> Use the "--format=hmac-md5" option to force loading these as that type >>>> instead >>>> Loaded 1 password hash (M$ Cache Hash 2 (DCC2) PBKDF2-HMAC-SHA-1 >>>> [128/128 SSE2 intrinsics 8x]) >>>> guesses: 0 time: 0:00:00:02 0.00% (2) c/s: 339 trying: 123456 - >>>> abc123 >>>> Session aborted >>>> $ john --format=hmac-md5 mscash2.john >>>> Loaded 1 password hash (HMAC MD5 [128/128 SSE2 intrinsics 12x]) >>>> guesses: 0 time: 0:00:00:02 0.00% (3) c/s: 1120K trying: 123man - >>>> 123mah >>>> Session aborted >>>> >>>> IMHO that's not very good. >>> >>> It was much worse until we forced hmac-md5 to lower precedence than >>> mscash. Now it is just cosmetic. That hash *is* a valid hmac-md5 hash, >>> with a salt of "$DCC2$10240#chatelain". >> >> Were these forms chosen for compatibility with other tools? I mean it's >> a pity to have a special, canonical form for a hash which clashes with >> other formats. > > It does not really clash, it just warns. It picks mscash2, emits the > notice and all is fine. Is it that bad? I loved when core got this feature. Problem is not in the warning itself. The warning is helpful. The problem is what it warns about. Suppose that Korelogic will include hmac-md5 in the upcoming contest. Then you cannot load these hashes without --format. Second problem: you cannot put both types of hashes in one file. Wouldn't it be better to have only one file with all hashes? I mean, to have one file instead of 20 is very convenient. Then you can select desirable part of it with --format. But this is impossible when there are collisions in canonical forms of given types of hashes. >>> We can stop this by >>> black-listing certain format salts. That's OK with me but in some way >>> it's a flawed path. >> >> Agreed. > > Just thinking out loud here: Let's say we could teach the hmac-MD5 > format that "it" should not emit that warning if the salt starts with > $DCC2$10240# - as opposed to always reject it in valid(). In the > (unlikely) case this was really a hmac salt, we could still use the hmac > format using --format. If we don't, it will pick mscash2 and not > complain. The only problem with this approach is it's not supported by > the current core and I'm not sure how we could implement that... or... > perhaps hmac-md5's valid() could take a peek at options.format (the > --format argument) and behave differently if unset... maybe this is > possible. I might try that some time. You mean to just silence the warning? I don't think it should be done without solving underlying problem. -- Alexander Cherepanov
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