Mekala Rama Rao¹, L Pratap Reddy¹, BHVS Narayana Murthy² and Maruti Sairam Annaluru², ¹Jawaharlal Nehru Technological University, India and ²Research Centre Imarat, India

Among the available private key cryptosystems, namely stream ciphers and block ciphers, the advantage of block ciphers is that they can be synchronized i.e. losing one ciphertext can not affect the correctness of the decryption of the following blocks. The encrypter used in block ciphers is a memoryless device. Block ciphers can be easily standardized due to the fact that they transmit information in blocks. But the disadvantage is that identical plaintexts result in identical ciphertexts. These data patterns are not hidden by the algorithm, resulting in higher influence of cryptanalysis process. Strength of block ciphers is exposed mainly into the exploration of weakness of cryptosystem. Barring this approach, strength estimation based on spurious key analysis is proposed in this paper. Till recent period, strength of a Cryptosystem is identified with the increasing key length. However, as per Shannon's proposal, strength of a Cryptosystem is dependent on Message also. Depending on the length of the message and the message space, we can estimate the actual strength of a Cryptosystem. As part of Shannon’s model, spurious keys is the concept adopted for identifying the strength of the Cryptosystem. Standard block ciphers; ARC2, Blowfish, CAST, DES; are evaluated to understand Shannon's principle of Information Theoretic approach using Spurious keys. Spurious key generation algorithm is designed, developed for evaluating the strength of Cryptosystem. Spurious key logic and Key scheduling logic are the two main blocks of the proposed approach. Behavior of Spurious keys is evaluated on message text of two languages, through selection of ten different sub key spaces. Each sub key space is independent of other and is constructed with 108 keys from the total key space of 264. It is observed that the number of spurious keys identified in each sub key space is almost close to similar value of the respective language. Comparison is made through this evaluation to explore algorithmic strength with that of computational burden of the algorithm, which will help selection of algorithm based on the critical requirements of the field. The very purpose is to examine the possibilities of considering spurious key analysis as one of the strongest methods to estimate the strength of a Cryptosystem. Spurious key analysis is performed on two sets of plaintexts containing two different scripts namely English and Devanagari.

Cryptography, Spurious Keys, Complexity, Strength of Algorithms, cryptanalysis, Language Based Security