It is important to keep this in mind as an exhaustive (brute force) attack on the DES standard would require 256 attempts (or 2^55 if we consider that there’s a 50% chance of finding the key halfway through computing the entire key length).ĭouble DES encrypts plaintext twice by two different keys of 56 bits in the following manner: P -> E(K1,P) -> X -> E(K2,X) = C OR Īrbitrary length plaintext data is divided into fixed length block of 64 bits ( P) and encrypted with key ( K1 – 56 bits in length) the resulting output (X) is encrypted with a different key ( K2 - 56 bits in length) which gives cipher text output (C – 56 bit output). However, effective key size is 56 bits because 8 bits out of the original 64 bits are used for parity checking. Why we don't use double DES? What is the 'meet in the middle' attack?ĭES (Data Encryption Standard) is a symmetric block cipher with key size of 64 bits.
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