Accepted: 19/Jul/2018, Published: 31/Jul/2018 Abstract—Cryptography is presently used for defensive purposes. Ciphers are used against passive attackers. Public key algorithms are used against an active attacker in man-in-the-middle attack. Digital signature is used for defending against a forger. E-cash systems are used against a counterfeiter and a double-spender. Pseudorandom bit generators are used against a next-bit predictor. Crypto virology is used for locating failures of protocols and vulnerabilities in design. For defending purpose Forward engineering is used.