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Date: Tue, 24 Jul 2012 01:19:37 +0400
From: Alexander Cherepanov <>
Subject: Re: mscash2 / hmac-md5 ambiguity

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.

On a more practical note, this means that you cannot build a robust 
system to run john for different kinds of hashes without --format. In a 
contest we get some hashes, determine their format and sort them into 
files named after formats. For me that's enough -- with it I can do 
things like that:

   for file in *.john; do
     format=`basename "$file" .john`
     john ... --format="$format" "$format.john"

But, as Frank pointed out, it's better if --format is not required -- 
less chances that a user will forget it. Probably we can ignore it until 
we actually meet hmac-md5.

> We can stop this by
> black-listing certain format salts. That's OK with me but in some way
> it's a flawed path.


Alexander Cherepanov

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