[dm-crypt] Recovering/Cracking passphrase

Roscoe eocsor at gmail.com
Thu Jul 1 15:02:04 CEST 2010


On Thu, Jul 1, 2010 at 10:34 PM,  <tesla1 at gmx.net> wrote:
>        I'm in a similar situation. Luckily, the Password is only 5 characters
>        long.
>
>        I try a different approach. I want to use John the ripper for cracking
>        the password.
>
>        Therefore I want to extract the sha1 key and salt from the luks Header.
>        I don't know if this is possible somehow. Next I want to create a file
>        from that data that is understood by JTR.
>
>        To test this approach I created sha1sums with sha1sum and libssl from a
>        3 letter word and put them in a password file. However I wasn't able to
>        crack that password, even with sha1 support compiled into JTR. I guess I
>        don't have the correct information in the password file and/or it is
>        wrong formatted.
>
>        Any help and suggestions on this approach is welcome!
>

The key is derived with PBKDF2, which is a bit more involved than a
simple salted SHA-1 password hash.

You could use JTR to generate your password list (-stdout), but would
need something else to do the PBKDF2 and checking (which is involved).
You could use cryptsetup for that, either with or without modification
depending on how slow you mind it being.

80^5 is still quite a few combinations to try, especially when you
have to do at least tens of thousands of iterations for each
combination.

Do you know much about your password? Is it all lower case? or only
alphanumeric?
Any information that cuts down your search space is valuable.

-- Roscoe


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