Introduction to Symmetric Block Cipher Jing Deng Based on Prof. Rick Han’s Lecture Slides Dr. Andreas Steffen’s Security Tutorial Cryptography plaintext Encryption ciphertext Decryption plaintext • Encryption algorithm also called a cipher • Cryptography has evolved so that modern encryption and decryption use secret keys • Cryptographic algorithms can be openly published • Only have to protect the keys plaintext Encryption Key KA ciphertext Decryption