A Linear Distinguishing Attack on Scream

A linear distinguishing attack on the stream cipher Scream is proposed. When the keystream is of length 2⁹⁸ words, the distinguisher has a detectable advantage. When the keystream length is around 2¹²⁰ the advantage is very close to 1. This shows certain weaknesses of Scream. In the process, the paper introduces new general ideas on how to improve the performance of linear distinguishing attacks on stream ciphers.