A NON-DETERMINISTIC PUBLIC KEY ENCRYPTON SYSTEM

A non-deterministic public key encryption system whereby a public key is generated from a private key using mathematical operations equivalent to exponentiation in finite fields. Thus an attacker is required to compute logarithms over finite fields. Encryption involves generating a random initialization key (R) which is used to (1) exponentiate the message receiver's public key (E) to produce initial values (K) for a pseudorandom binary mixture generator, and to (2) compute an open key (Q) by exponentiating an initial known generator state (a.sub.0). A ciphertext (C) is produced from plaintext (P) by clocking the mixture generator from the initial value (K) and combining the output keystream with the plaintext (P). The open key (Q) is attached to the ciphertext prior to transmission. Decryption involves extracting the open key (Q) and exponentiating this by the message receiver's private key (D) to compute (K) which is then used to set the initial value of a mixture generator. The mixture generator is clocked and its output keystream combined with the ciphertext (C) to produce plaintext (P). The invention may be implemented in special purpose hardware or in software for a general purpose processor.