02Oct Cryptography

Cryptography is a tool that can be used for sending information in such a way that the system through which it passes, do not know anything. It is used to keep information confidential and to ensure its integrity and authenticity. All modern cryptographic system is based on Kerckhoff’s principle of having a publicly known algorithm and a secret key. Many cryptographic algorithms use complex transformation involving substitutions and permutations to transform plain text into the cipher text. However, if quantum cryptography can be made practical, the use of one time pads may provide truly unbreakable cryptosystems.

Cryptographic algorithms can be divided into symmetric-key algorithms and public-key algorithms. Symmetric-key algorithms manage the bits in a series of rounds parameterized by the key to turn plain text into cipher text. Triple DES and Rijndael (AES) are the most popular symmetric key algorithms at present. These algorithm can be made use in electronic code book mode, cipher block chaining mode, stream cipher mode, counter mode and others.

Public-key algorithms have the property that different keys are used for encryption and decryption and that the decryption key cannot be derived from encryption key. These properties make it possible to publish a public key. The main public key algorithm is RSA, which derives its strength from the fact that it is very difficult to factor large numbers.