Analysis of Some Security Criteria for S - boxes in Blowfish Algorithm

S-box is keystone of modern symmetric such as block and stream ciphers. It is essential component in the layout of any block system. The properties of S-boxes in Blowfish algorithm (BA) namely; Avalanche Criterion (AVAL), Strict Avalanche Criterion (SAC) and Bit Independence Criterion (BIC) are used to measure the security of the S-boxes in BA. This paper attempts to analyze these properties (AVAL, SAC and BIC) in blowfish algorithm, after which the results are compared with S-boxes in Rijndael and Safer K-64. Twelve experiments have been conducted on the S-boxes in BA using three different types of encryption keys (Eks) with the purpose to examine the effect of entropy of the Eks on the security of the S-boxes in BA. The first ten experiments are conducted with ten different random Eks; the remaining two experiments are carried out with non-random Ek, one experiment with high entropy Ek and the last experiment with low entropy Ek. The analysis of this study proved that the S-boxes in BA satisfied the above properties with maximum error values of 0.0518, 0.3594 and 0.4725 for AVAL, SAC and BIC respectively. The security of Sboxes was not affected by the entropy of Eks in BA. C++ is used in the implementation of the BA while MATALAB programming (Mathworks R2012a) is used in the implementation of the properties (AVAL, SAC and BIC).