Cryptography

Contents

Evolution of cryptography

Theory

Encryption and decryption

Data Encryption Standard

Public key cryptography

Symmetric key Cryptography

ENCRYPTION & DECRYPTION

cryptography referred almost exclusively to encryption, the process of converting ordinary information (plaintext) into unintelligible gibberish (ie, ciphertext). Decryption is the reverse, moving from unintelligible ciphertext to plaintext. A cipher (or cypher) is a pair of algorithms which perform this encryption and the reversing decryption.

The detailed operation of a cipher is controlled both by the algorithm and, in each instance, by a key known only to the communicants,occurred as follows:

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