Issues and Operation Modes for Block Ciphers and Femtocells

Cryptography is the process of writing using various methods ("ciphers") to keep messages secret. In modern times cryptography is considered to be a branch of both mathematical and computer science. At one time the subject was mainly a linguistic one, the key concern being the ability to recognize words and make words unrecognizable with a simpler cipher. Public key cryptography is a modern technique. Encryption key is called the public key. Decryption key is called the private key. To attack a cipher is to attempt unauthorized reading of plaintext, or to attempt unauthorized transmission of cipher text. The Data Encryption Standard (DES) defines an indexed set of permutations acting on the message space. It is widely used in Banking. There are basically two ways to make a stronger cipher: the stream cipher and a block cipher. A stream ciphers are commonly used nowadays in hardware applications. One of the best known early block ciphers is the Play fair system.