Distinguishing attack on common scrambling algorithm

Common Scrambling Algorithm (CSA) has been used to encrypt european cable digital television signals since 1994. Although, the key size of CSA is small, up to now, there haven’t any effective crypto results which can break the algorithm totally. Based on the idea of slide resynchronization attack, a distinguishing attack which can distinguish the keystream of the Stream Cipher (SC) from a purely random sequence with computational complexity of O(2 15 ) is proposed. According to the distinguishing attack, the 64 bit initial key can be recovered with computational complexity of O(2 55 ).