Symmetric Key Cryptography: Cryptographic Techniques

This is the fifth in a series about cryptography; an extremely important aspect of computer science and cyber security. It reviews how the XOR logical operation can be used to encrypt at the bit level in symmetric key cryptography, then shows how this can be combined with permutation steps to create an even stronger cipher. It mentions a number of principles used in modern day block ciphers such as DES and AES, including the Feistel cipher, block ciphers, block chaining, the use of multiple sub keys and multiple encryption rounds.