Security Test On Cryptographic Algorithms And Design Of Key Cryptographic Components

Cryptographic algorithms have played fundamental roles in information security. Standardization of cryptographic algorithms has been carried out in many countries, which has resulted in a new high tide of cryptographic algorithm design. In the process of collecting algorithms, a very key proplem is how to evaluate an algorithm correctly. Security is the most important evaluation factor which contains the stability of mathematical basis, resistence against attacks, randomness and so on.Under this background, this dissertation will focus on the randomness tests on cryptographic algorithms. Besides, security tests on key cryptographic components and how to construct secure and effective cryptographic components are investigated in this dissertation. Several principal achievements have been obtained as follows:1) Security tests on all kinds of cryptographic algorithms are summarized, and on the basis of randomness tests on block ciphers, stream ciphers and pseudorandom number generators, the randomness tests on hash functions are newly added including digest randomness test, message diffusibility test and key diffusibility test.2) A kind of randomness test on key schedule algorithm of block ciphers is designed. Now the randomness tests on block cihers are limited to encryption algorithms. However, key schedule algorithm is also an important part of a block cipher, bad key schedule algorithm can easily cause some attacks on the whole algorithm. An ideal key schedule algorithm should ensure the statistical independence among the round keys. A new test algorithm is designed in this dissertation which can compute the independence degree of all round keys.3) A kind of bias test on S-boxes is proposed. It depends on such a basic truth: in the space constructed by all Boolean functions, if a Boolean function is randomly chosen, the XOR sum of all output vectors should equal any possible value with thesame probability. The basic truth can be extended to S-boxes. For a S-box with good randomness, some input bits and output bits are fixed. When the values of input bits are changed, several independent sub-Boolean functions can be obtained and the XOR sum of their output vectors should be equally possible. Here, the probability bias of output XOR will be computed with all sub-Boolean functions considered. This bias test reflects the randomness degree of S-boxes.4) A set of S-boxes with good cryptographic properties have been designed. First how to improve the cryptographic properties of S-boxes by changing the local outputs of S-boxes with some rules is investigated. And how to evolutionally design bijective S-boxes is also studied in this dissertation. Under the given evolutionary strategy, a large number of bijective S-boxes with high nonlinearity and low differential uniform can be obtained. Besides, a RC5-based method to construct S-boxes is also proposed. This method fully makes use of the secure and simple characteristics of the well known RC5 algorithm by abstracting the structure of RC5 to construct popular 8×8 S-boxes.