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An Algorithm is considered computationally secureif it can not be broken with standard resources, either currentor future. In this paper we have introduced a new block cipheralgorithm named X-MODDES. It is unique independentapproach which uses several computational steps along withstring of operators and randomized delimiter selections byusing some suitable mathematical logic. X-MODDES isspecially designed to produce different cipher texts by applyingsame key on same plain text. Thus a new protocol has beendesigned to encrypt a given text, which allows a higher levelsecurity as compare to MODDES. The Algorithm issuccessfully implemented on text file, corresponding digitalimage file and audio file. Here we have also tried to highlightthe performance of some well known data algorithms like DES,Triple-DES, AES (Rijndael), MODDES, and compare themwith the X-MODDES. Finally it has been proved that XMODDESis one of the best performing partial symmetric keyalgorithm among the above mention algorithms particularlyfor the text message with limited size.
Keywords - MODDES, Cryptanalysis, Modified Secure CodeSequence, Transposition, Substitution
Different algorithms offer different degrees of security; itdepends on how hard they are to break. If the cost required tobreak an algorithm is greater than the value of the encrypteddata then we probably consider safe. Here, we have used theword “probably” because there is always a chance of newbreakthroughs in cryptanalysis. In this paper we haveproposed several modifications of MODDES  which isa partial symmetric key algorithm, and introduced a newmodified algorithm namely X-MODDES. Here we are using32-bit key along with some specific changes on MODDES.These modifications on MODDES include addition ofseveral secure computational steps like transposition,substitution and binary operations etc. In transposition, weexchange the position of text which is shown in fig 1. Thereafter, the substitution methodology has been introducedalong with binary logic and some particular changes ofMODDES algorithm. X-MODDES algorithm also protectsthe cipher text from the attacks like Brute-force attackbecause X-MODDESS is not fully dependent on the key andcode can not be deciphered by applying all possiblecombinations of keys.Figure 1. Transposition Process
II. ENCRYPTION PROCEDURE OF X-MODDES
In this algorithm, we have taken two predefined stacksalong with a logic based lookup table concept. The first stackconsists of different combinations of strings of operators andanother stack consists of combinations of several delimiters,which are chosen randomly on the basis of a predefinedmethod which makes the code sequence more secure. Thesteps of the algorithm are given below.