Cryptanalysis Of The Stream Cipher SOSEMANUK

SOSEMANUK as a software-oriented stream cipher was designed by C.Berbain and O.Billet, which is one of the final winner algorithms of the European stream project eSTREAM. In order to achieve a high degree of security and efficient requirements, the algorithm mainly combines the design advantages of stream ciphers SNOW2.0 and block cipher SERPENT.The paper introduces the implement of SOSEMANUK and analyzes the design rationality, then compares the performance of hardware implementation and software implementation with others winner algorithms in the project eSTREAM. Finally, security analyses of SOSEMANUK are proposed, which mainly focus on the guess and determine attack.Compared with the existent guess and determine attack, the following results are achieved:By analyzing the weakness in the design of the stream cipher SOSEMANUK, presenting guess and determine attack on it, and then guess 7-words internal state, each word contains 32 bits. From the above-mentioned two aspects, all the internal state can be achieved. By checking the keystream, the algorithm can determine the only internal state. The attack requires only 6 keystream words, leading to a complexity of O (2¹⁹⁴). The results show that the algorithm which has been analyzed exists security vulnerabilities, moreover the computational complexity of attacks is far lower than the designers claimed O (2²⁵⁶).