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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.sub.B) 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.

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First Claim