Known Plaintext Attack

Related Concepts

Block Ciphers; MAC Algorithms; Stream Cipher; Symmetric Cryptosystem

Definition

Known plaintext attack is a scenario in which the attacker has access to pairs (P _i ,  C _i ), i = 1, …, N of known plaintexts and their corresponding ciphertexts. This attack is considered to be highly practical, especially if the amount of pairs N is not too large. This attack scenario is more practical than the chosen plaintext attack. Probable word method which is a popular technique for solving classical simple substitution or transposition ciphers is an example of a known-plaintext attack. Another example is the cryptanalysis of the German Enigma cipher (crypto machines or [1]) using the so-called bombs. It relied heavily on properly guessed opening words of the cryptograms (which were at the time called cribs). One of the most popular cribs was “Nothing to report.” In modern cryptography, linear cryptanalysis is a typical example of a known plaintext attack.