Modern cryptography has virtually no provably secure constructions. Starting from the first Diffie–Hellman key agreement protocol (Diffie & Hellman, 1976) and the first public key cryptosystemRSA (Rivest et al., 1978), not a single public key cryptographic protocol has been proven secure. Note, however, that there exist secure secret key protocols, e.g., the one-time pad scheme (Shannon, 1949; Vernam, 1926); they can even achieve information–theoretic security, but only if the secret key carries at least as much information as the message.