Linear cryptanalysis is a method used to analyze and break symmetric key ciphers. It relies on finding linear approximations between the plaintext, ciphertext, and key bits. By exploiting these relationships, attackers can gain information about the secret key used in the encryption process. This technique was first introduced by Mitsuru Matsui in the 1990s and has since been applied to various encryption algorithms. The effectiveness of linear cryptanalysis depends on the structure of the cipher and the amount of known plaintext-ciphertext pairs available to the attacker.