Cryptography to the Rescue!

Symmetric-key Cryptography for Data Privacy and Integrity

• Data encrypted and decrypted with same key

• Classical examples: Caesar cypher, one-time pad, Enigma Machine

• Fast, tested (secure?) algorithms available: DES, RC4, IDEA....

• Strength of scheme largely depends on size of key

Great, but how do the two parties get the shared, secret key?