Realization of Perfect Secrecy: The One-time Pad (1917)
P = C = K = n bit strings
EK(p) = bitwise xor of K and p = c.
DK(c) = bitwise xor of K and c = p
Problems:
- amount of key that must be communicated securely equals amount of plaintext
- severe key management problems since can use each key for only one encryption
(vulnerable to known plaintext attack)