Cryptanalysis of GSM Ciphers


The stream cipher Algorithm A5 used to encrypt GSM telephone communication. The Algorithm A5 consists of three versions (A5/1, A5/2and A5/3). In the current standard protocol the three algorithms share the same secret key. Thus in this paper we select the weakest algorithm A5/2,attack the algorithm and extract the secret key in a cipher text-only attack,using the weaknesses of the cipher and majority functions. Then using the secret key to decrypt the communication even encrypted under the algorithms A5/1 and A5/3.