[RC5] Another way to win DES-II (joke?)

Michael Tsao tsaobug at geocities.com
Fri Jul 31 20:05:20 EDT 1998


> ....  But I did read a method for cracking
> DES where
> you try every key with a given plaintext and then store the
> cyphertext.  Then to decrypt a message that has this known plaintext, you
> simply look up the key.

That's a good idea.  However, in practice, it's often foiled by applying any
standard form of data compression (WinZip would work fine) to the plaintext
before sending it through the encryption process.  Then (particularly with a
compression method like Huffman, whose coding keys depend on the overall
distribution of plaintext characters, but NOT with a dumber method like RLE)
the unknown portion of the plaintext affects the "appearance" of the
compressed known plaintext.  PGP uses this step as part of its encryption
process.  I don't know about DES, but one would think they'd do it, too.

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