Enhanced Caeser Cipher to Exclude Repetition and Withstand Frequency Cryptanalysis

Abstract

Cryptography is the art of encoding messages into an unreadable form from a sender and re-transforming back to its readable form at the receiver end. This is an enhanced Caesar cipher against frequency analysis using bidirectional shift. This algorithm encrypts message bit by bit or character by character (stream cipher) and uses one key ideology (symmetric key cipher), the sender encrypts the message before transmitting and the receiver decrypts upon receiving using the same key as the one used for the encryption. It shifts the plain text characters to different direction which eliminates repetition of characters in the cipher text. Previous versions of Caesar cipher had only 26 English alphabets to be encrypted, which the attacker knew that there were only 26 choices to choose from, to determine the plain text. And when the alphabet of the same type are encrypted, they will have the same symbol representing each, which gives hint to attacker on how to break it by using frequency cryptanalysis. The enhanced method (Enhanced Caesar cipher) has 95 characters as digital messages as against 26 alphabets. Based on this method, the sender will transposition the bits in the message according to their sequence arrangement (odd and even position) to shift the characters in the odd position to the left and characters in the even position to the right side, based on the key given by the user, as the key to both shifts. Shifting the plain text to different directions mitigates the problem of repetition which the previous version suffers from. To make decryption more difficult, each character will switch position with the next to randomize their arrangement. The cipher was successfully developed and working accurately. It was developed on java platform using java eclipse IDE and NETBEANS IDE 7. 1. 2. It has successfully passed all the tests and proven its accuracy obtaining the result of 100% repetition free. Thus, the proposed method is highly resistant to frequency analysis. This provides more security than the earlier versions and it serves as an option to be integrated with other algorithms to strengthen the security.

Keywords: Caesar Cipher, Cryptography, Repetition Exclusion, Encryption, Decryption, Shift, Switch, Symmetric-Key Cipher, Key Generation

View PDF