Security Analysis Of The Balanced Shrinking Generators

Shannon showed in his fundamental paper in 1949 that this encryption system isunconditionally secure when the length of key equal to the length of the message. This propertymeans that no matter how big or fast a computer the attacker has, she can never find out whichplaintext was sent, for example as Vernam cipher in F₂, the ciphertext is computed by theexclusive or (xor) of the message bits with the key bits, i.e. let the message bits be denotedm=m₁m₂...m_l and the key bits as K=k₁k 2... k_l,Therefore, research on the security of key generator that generate a long period keystreamfrom a short key or initial state has became the main problem in Symmetric-key primitives. Sothe design and analysis of key generator became the key problem in the research of streamcipher.Clock-controlled sequence generator is a class of keystream generator in stream cipher, suchas the famous stop/go generator, the Gunther alternative step generator, the shrinking generatorand the self-shrinking generator. The main design ideals of clock-controlled generator ischanging the position of the output unit of linear feedback shift register, to make the outputsequence generated by the generator have good properties in cryptology or undistinctive with thetrue random sequence by known methods. These generator have arosed many concerns aroundthe world more than 20 years and many results have been presented by many famouscryptographist.In this paper, we concentrate on the properoties and security of the balanced shrinkinggenerator, especially the sucurity analysis of it. At first, the results of cryptanalysis ofclock-controlled generator developed during the past 20 years are described briefly and clearly.And then based on understanding techinique and algorithm, we dig more on its propertie,improving the lower bounder of linear complexity, propose a new quantitative index ratio ofequivalent keys, and then present the attack to the balanced shrinking generator using fastcorrelation attack and distinguish attack techinique and algorithm. At last, we have a simple talkabout these classic methods about implement and optimization.