ABSTRACT

The art of keeping messages secret is cryptography, while cryptanalysis is the study attempted to defeat cryptographic techniques. Cryptography is used to protect information from illegal access. It largely encompasses the art of building schemes (ciphers) which allow secret data exchange over insecure channels [351]. The need of secured information exchange is as old as civilization itself. It is believed that the oldest use of cryptography was found in non-standard hieroglyphics carved into monuments from Egypt’s Old Kingdom. In 5 B.C. the Spartans developed a cryptographic device, called scytale to send and receive secret messages. The code was the basis of transposition ciphers, in which the letters remained the same but the order is changed. This is still the basis for many modern day ciphers. The other major ingredient of many modern-day ciphers is substitution ciphers, which was used by Julius Caesar and is popularly known as Caesar’s shift cipher. In this cipher, each plaintext character was replaced by the character 3 places to the right in the alphabet set modulo 26. However, in the last three decades cryptography has grown beyond designing ciphers to encompass also other activities like design of signature schemes for signing digital contracts. Also the design of cryptographic protocols for securely proving one’s identity has been an important aspect of cryptography of the modern age. Yet the construction of encryption schemes remains, and is likely to remain, a central enterprise of cryptography [134]. The primitive operation of cryptography is hence encryption. The inverse operation of obtaining the original message from the encrypted data is known as decryption. Encryption transforms messages into representation that is meaningless for all parties other than the intended receiver. Almost all cryptosystems rely upon the difficulty of reversing the encryption transformation in order to provide security to communication [353]. Cryptanalysis is the art and science of breaking the encrypted message. The branch of science encompassing both cryptography and cryptanalysis is cryptology and its practitioners are cryptologists. One of the greatest triumph of cryptanalysis over cryptography was the breaking of a ciphering machine named Enigma and used during Worldwar II. In short cryptology evolves from the long-lasting tussle between the cryptographer and cryptanalyst.