摘要：Many classical cryptosystems are developed based on simple substitution. Hybrid cryptosystem using byte substitution and variable length sub key groups is a simple nonlinear algorithm but the cryptanalyst can find the length of each sub key group because the byte substitution is static and if the modulo prime number is small then byte substitution is limited to first few rows of S-box. In this paper an attempt is made to introduce the nonlinearity to the linear transformation based cryptosystem using dynamic byte substitution over GF (28). The secret value is added to the index value to shift the substitution to a new secret location dynamically. This adds extra security in addition to non-linearity, confusion and diffusion. The performance evaluation of the method is also studied and presented.
关键词：Dynamic Byte Substitution; Hill Cipher; Pseudo-random Numbers; Sub Key Groups.
