Abstrato

MODIFIED MULTI WAY FEEDBACK ENCRYPTION STANDARD VER-2(MWFES-2)

Saptarshi Chatterjee, Debdeep Basu , Ankita Bose, Surajit Bhowmik and Asoke Nath

Nath et al developed a method Multi Way Feedback Encryption Standard Version-I [18] recently, where the authors used both forward and backward feedback from left to right and from right to left on the plain text along with the key. In MWFES-I, the ASCII value of plain text is added with key and forward feedback (FF) and backward feedback (BF) to obtain intermediate cipher text. The initial FF and BF are taken to be 0. The intermediate cipher text is taken modulo operation with 256 to get cipher text. This cipher text is taken as feedback for the next column. In the second round we calculate the cipher text from the RHS. In the MWFES-II, the authors have used a much more general approach. The FF and BF have been applied using skip by n-columns; where „n‟ can be 0 to any number less than the length of the plain text. In the present method (Modified Multiway Feedback Encryption Standard, Version -2), the authors have introduced two different skips „n1‟ and „n2‟. We perform „n1‟ skips for forward feedback (that is, from the left), and „n2‟ skip for backward feedback (that is, from the right). „n1‟ and „n2‟ may or may not be equal and is taken as a function of the generated keypad. The authors applied the present method on some standard plain texts such as 1024 ASCII „0‟, 1024 ASCII „1‟, 1024 ASCII „2‟ and 1024 ASCII „3‟ and the frequency analysis shows the encrypted texts are totally random. Initially, the user has to enter a secret key (seed). The key-expansion algorithm generates an enlarged keypad of the size of the plain-text from the seed. This keypad is used for further encryption and decryption. The present method is very effective as the encrypted text changes drastically on varying the skip „n1‟ and „n2‟. Modified MWFES-2 can be applied to encrypt any short message, password, confidential message or any other important document. The results show that the present method is free from standard attacks such as differential attack, known plain text attack etc.