john-users - Cracking DES with Probable Plaintext attack?

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Message-ID: <197273.51344.qm@web113704.mail.gq1.yahoo.com>
Date: Sun, 28 Mar 2010 07:05:08 -0700 (PDT)
From: John Doe <johndoe5542@...oo.com>
To: john-users@...ts.openwall.com
Subject: Cracking DES with Probable Plaintext attack?

Hi,

i have a DES encrypted file and can assume that the plaintext contains ASCII letters with some spaces, .!?-chars and so on.
Is it possible to crack it with john?

I 've looked into the code, bit-slice DES, sboxes and so on --> is my assumption true that this works only for known-plaintext attacks? (I have the ciphertext and plaintext, and want the key? - btw - when is this attack useful? I usually don't have the plaintext, right?)

Last question: Is it possible to crack DES with no huge cost effort in reasonable time (2 weeks)? I 've calculated, and came to the result that the machine would have to brute-force 59571 million keys/s (my current threaded cracker checks 4 million keys/s on a Pentium Dual-Core 2,6Ghz/core). Looks like it won't be possible with high-CPU Amazon EC2 either.

Thanks,
John

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