Abstract: A cryptographic communication system is disclosed which permits computer users to authenticate themselves to a computer system without requiring that the computer system keep confidential the password files used to authenticate the respective user's identities. The invention is useful in that it prevents a compromised password file from being leveraged by crafty hackers to penetrate the computer system.

Abstract: 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 offline "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 C.sub.A and sends R(C.sub.A) to Bob; (4) Bob decrypts to get C.sub.A, generates a random challenge C.sub.B and sends R(C.sub.A, C.sub.B) to Alice; (5) Alice decrypts to get (C.sub.A, C.sub.B), compares the first against the challenge and sends R(C.