On The Design And Security Analysis Of Block Ciphers

ABSTRACTThis thesis is devoted to the design and security analysis of block cipher systems. Main contributions of the workare as follow:(I)We design a non-standard calculating device: non-homogeneous-cany-module-addition-group. Its properties and calculating amount is discussed and an application to MA structure of the block cipher IDEA is given to overcome the potential weakness nontrivial transparency of the MA structure?(2)We present a strengthening method to the block cipher named random group. We point its advantage in pseudorandomness and ability against differential ctyptanalysis. The application of the random group to IDEA is valuable by our analysis to calculating amount and security.(3)We present an attack method to block ciphers: a new class of higher order differential cryptanalysis. We analyze single round SAFER by this method.(4)We carefully address ourselves to design and drawbacks of the block cipher SAFER and present two modification algorithms. On the basis of simplicity and transparency of SAFER, we get E/D similarity and more secunty.(5)We give a modification algorithm SAGER+M of the strengthening version SAFER+ of SAFER We get El!) similarity and the same security.(6)We give some modification algorithms of CAST, a candidate of AES. The modified algorithms are more compact with better covering features, better diffusion features and ED similarity.(7)We change the non-linear key device of RC6. a candidate of AES. This change obviously decreases the calculating amount and converts single-direction-diffusion to double-direction -diffusion. On this basis we present several modification algorithms to get ER) similarity.(8)We discuss the basic theory of block cipher general key schedule, that is. generation of pseudo sequence. We present the self-rotation-shrinking-series. We discuss its algebraic structure, minimum period, linear complexity and the multipleness of the generation.(9)We define the Logarithmic Sequence. We discuss its linear complexity, the stability of the linear complexity, pseudorandomness. As an example. we discuss generalized Legendre sequence and generalized Jacobi sequence. Conclusion: Logarithmic sequence seems a good pseudo sequence.(10)We present a keyed-authentication-code scheme by block cipher and discuss its security.(11)We give some registrations about block cipher's design, security, and an application to iterated Hash function.