Research On A Word Based Stream Cipher Dragon

An important study area in modern cryptography is stream cipher. Nowadays, secure military and diplomacy communications in most countries are using stream cipher, for its ideal mathematical analysis tools and other advantages. All these make stream cipher a hot study field. In order to find a good stream cipher algorithm as world standard for data encryption, Europe has launched ECRYPT project which is a four years information security project with wider scope after NESSIE, and the ECRYPT Stream Cipher Project has collected many good stream cipher algorithms. At present, the research and analysis of the candidate algorithms to ECRYPT is a hot spot of stream cipher. Dragon is one of the candidates to the ECRYPT.Dragon is a new algorithm based on the word based stream cipher which uses non-linear feedback shift registers and S boxes. It operates on key sizes of 128 and 256 bits. The main work is following. We study its mechanism, performance and design principles and discuss the security against the well-known cryptanalysis. It is pointed out that Dragon is secure against the brute and TMD attack. There are four steps calculating the bias of Dragon by using linear cryptanalysis principle. Then linear approximation can be constructed and finally establish the expression for the bias. By analyzing the expression for the bias by matlab we find that: when the hamming weight of linear combination m=7, the bias achieves its maximum value 2 ^ (-75.808035).