Cryptosystem

A cryptosystem consists of sets , , and functions:

Such that for all and Breaking Cryptosystems Key Equivocation Message Equivocation Perfect Secrecy Unicity Distance

Lemma

Message EquivocationKey Equivocation

Proof

Since , we know Now calculate:

Exmples

Substitution cipher Vigenere Cipher Stream Cipher One Time Pad Rabin Cryptosystem RSA Cryptosystem Diffie Hellman Key Exchange