[SEC] Cryptography II
Cryptography II Content Symmetric Encryption Block Ciphers SP-Networks The advanced Encryption Standard Modes of Operation Hash Functions The Birthday Paradox Message Authentication Codes Symmetric Ciphers Symmetric ciphers are divided into two categories: Stream cipher: each plaintext corresponds to one ciphertext Block cipher Block Ciphers Block ciphers use a key to encrypt a fixed-size block of plaintext into a fixed-size block of ciphertext If you’re careful, you can convert between block and stream ciphers using modes of operation SP-Networks Claude Shannon suggested that all that was required for a strong cipher was repeated substitution and permutation SP-Networks combine a substitution process with a permutation into a single round Rounds are then repeated enough times to ensure the algorithm is secure What does it mean by “permutation”? It means that the ciphertext can be translated back to plaintext Substitution Boxes - Add confusion by re