Spurious Key Approach on Indic Scripts for Strength Estimation of a Cryptosystem

Abstract

Identifying the strength and weakness are two major aspects in cryptology for providing a match between a  cipher and specific application. Several attempts are reported in literature which witness the ways of exploiting the weakness of cipher and break it. This process expanded simultaneously in two directions. One dimension is to identify the various weaknesses of key and the other is to identify the pitfalls of algorithm. Both directions are found to be successful in breaking the ciphers to the extent of few rounds. Success rate of cryptanalysts forced  cryptographers further development of ciphers with increase in  complexity of algorithm as well as length of key. Availability of high computational powers is at a race while handling increased complexity of any cipher. A cryptosystem is composed algorithm, key and message text for its functionality. Significance of message is undermined in the existing methods of cryptanalysis by considering it as a mere bit stream. More and more methods are developed to guess those bits (either key bits or message bits). It is important to note that several cryptanalysts suggested that handling the randomness of message text could be the key factor for higher success rate of cryptanalysis. A model called spurious key analysis is presented in this paper using English, Devanagari and Telugu message texts. Four block ciphers ARC2, Blowfish, CAST and DES, which  are chosen for evaluation spurious key approach. The observations about improved spurious nature with non-English plaintexts are experimentally tested and results are discussed in order to provide more amount of confusion to cryptanalyst.