出版社：Academy & Industry Research Collaboration Center (AIRCC)
摘要：Among the available private key cryptosystems, namely stream ciphers and block ciphers, theadvantage of block ciphers is that they can be synchronized i.e. losing one ciphertext can notaffect the correctness of the decryption of the following blocks. The encrypter used in blockciphers is a memoryless device. Block ciphers can be easily standardized due to the fact thatthey transmit information in blocks. But the disadvantage is that identical plaintexts result inidentical ciphertexts. These data patterns are not hidden by the algorithm, resulting in higherinfluence of cryptanalysis process. Strength of block ciphers is exposed mainly into theexploration of weakness of cryptosystem. Barring this approach, strength estimation based onspurious 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 actualstrength of a Cryptosystem. As part of Shannon’s model, spurious keys is the concept adoptedfor identifying the strength of the Cryptosystem. Standard block ciphers; ARC2, Blowfish,CAST, DES; are evaluated to understand Shannon's principle of Information Theoreticapproach using Spurious keys. Spurious key generation algorithm is designed, developed forevaluating the strength of Cryptosystem. Spurious key logic and Key scheduling logic are thetwo main blocks of the proposed approach. Behavior of Spurious keys is evaluated on messagetext of two languages, through selection of ten different sub key spaces. Each sub key space isindependent of other and is constructed with 108 keys from the total key space of 264. It isobserved that the number of spurious keys identified in each sub key space is almost close tosimilar value of the respective language. Comparison is made through this evaluation to explorealgorithmic strength with that of computational burden of the algorithm, which will helpselection of algorithm based on the critical requirements of the field. The very purpose is toexamine the possibilities of considering spurious key analysis as one of the strongest methods toestimate the strength of a Cryptosystem. Spurious key analysis is performed on two sets ofplaintexts containing two different scripts namely English and Devanagari.
