The security of an online system is the foremost necessity nowadays. With huge growth of the IT power and with the invention of new technologies, the number of threats a user faces is growing exponentially. Cryptography is a combination of security engineering and mathematics. It is the best technology for securing distributed systems. Cryptography consists in processing plain information by applying a cipher and producing encoded output, unknown to a third-party who does has no idea about the key. In cryptography both encryption and decryption phase are processed by one or more keys. Encryption is extremely important for a safe and secure environment for the computers and the Internet.