Composite Transposition Substitution Chaining Based Cipher Technique

摘要

In this paper, variable block length based character / bit level transformation has been proposed for encryption, where a block of 16 characters/128bits has been taken into account. The block is passed through a substitution operation followed by various transpositions using multi dimensional array. The block is operated with its one-time sub key which produces intermediate output of the same length. Consecutive 8 characters/64 bits are taken from the stream of plain text with the previous text block which produces a block containing stream of 192 bits. This is used as current text block in order to produce a new text block containing 24 characters using same techniques. Another 8 characters are taken with previous block and the same operations are performed to produce a block of 256 bits. If the plain text contains greater than 32 characters i.e. 256 bits, then every 256 bit block is XORed with the previous 256 bit block except the first block. Finally bits are selected randomly from MSB position and the selected bits are processed through a special substitution technique to generate the final encrypted block.