Private Key Systems

• Examples: DES, AES, IDEA, RC5, RC6, Blowfish, Twofish
• Same key is used for both encryption and decryption. The key must be kept secret from outsiders.
• Work only with fixed-sized chunks of data (generally 64-256 bits) - message must be broken up into chunks and then encrypted. Output size is generally same as input size.
• Use combinations of algebraic (add, multiply, etc) and bitwise (xor, rotate, etc) operations and table lookups (sboxes) to "mix" key and data.
• Changing a single bit of data or key will change approximately 50% of output bits.