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Date: Mon, 23 Jul 2012 12:59:12 +0200
From: magnum <>
Subject: Re: mscash2 / hmac-md5 ambiguity

On 2012-07-23 12:55, Frank Dittrich wrote:
> On 07/23/2012 12:46 PM, 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". We can stop this by
>> black-listing certain format salts. That's OK with me but in some way
>> it's a flawed path.
> hmac-md5 doesn't have the "split() method unifies case" flag set, but
> mscash2 has.
> could we change that in a way that one format uses uppercase, the other
> lowercase? Or would breaking backwards compatibility hurt too much?
> If hmac-md5 is less likely to be cracked with john, we could convert
> that one to upper case hex, and drop the flag from mscash2.

The hmac format should unify case too, it's a to-do (and a bug). IMHO
the only really good solution is to accept the harmless warning. We get
very similar warnings in many other situations.


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