A cryptographic protocol for secure communications

A cryptographic communication system. The system, which employs a novel combination of public and private key cryptography, allows two parties, who share only a relatively insecure password, to bootstrap a computationally secure cryptographic system over an insecure network. The system is secure against active and passive attacks, and has the property that the password is protected against off-line "dictionary" attacks. If Alice and Bob are two parties who share the password P one embodiment of the system involves the following steps: (1) Alice generates a random public key E, encrypts it with P and sends P(E) to Bob ; (2) Bob decrypts to get E, encrypts a random secret key R with E and sends E(R) to Alice; (3) Alice decrypts to get R, generates a random challenge CA and sends R(CA) to Bob ; (4) Bob decrypts to get CA, generates a random challenge CB and sends R(CA, CB) to Alice; (5) Alice decrypts to get (CA,CB), compares the first against the challenge and sends R(CB) to Bob if they are equal ; (6) Bob decrypts and compares with the earlier challenge ; and (7) Alice and Bob can use R as a shared secret key to protect the session.