On 8 Mar 2003, Kryptik Logik wrote: > 1. In DES algorithm, given an encrypted text and the corresponding plain > text for that is it possible to retrieve the key. Essentially, how secure > is DES to known-plain text attack. 1 plaintext + 1 matching ciphertext + 2^55 work -> key > I read some where that it is quite resistant requiring 2^55 plain texts > to get the key but why is this so? What particular feature of the > algorithm makes it this way? I think you're thinking of linear or differential cryptanalysis here. These are attacks which make use of a lot of data to analyze patterns in the text. They are not particularly practical, as 2^55 blocks = 256 petabytes. I think it's highly unlikely that you'll be encrypting that much data with DES anytime soon. In any case, I don't think secprog@ is the right place for questions like this. Try cryptographyat_private, the general sanity level is much higher there than in cypherpunks or sci.crypt. -Jack
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