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We present some practical security protocols that use private-key encryption in the public-key style. Our system combines a new notion of private-key certificates, a simple key-translation protocol, and key-distribution. These certificates can be administered and used much as public-key certificates are, so that users can communicate securely while sharing neither an encryption key nor a network connection. Suppose as usual that Alice and Bob want to communicate securely. Conventional private-key authentication requires that they share a secret key, but if instead each shares a key with a translator Tom, Alice and Bob can avoid sharing directly by using Tom as an intermediary [9, 11, 5, 2]. Bob writes a message for Alice, but encrypts it for Tom's eyes only; when Alice wants to read this message, she asks Tom to translate its encryption into her key. Tom is trusted not only to keep the message secret, but also to sign the message as Bob's proxy: 1. B 0! A : fA, msggK b;t 2. A 0! T : ...

Abstract not found

Dispute of transactions is a common problem that could jeopardise business. Hence non-repudiation services are essential in business transactions which provide evidence to enable dispute resolution. To be eligible as non-repudiation evidence, the digital signature on an electronic document should remain valid until its expiry date which is specified by some non-repudiation policy. The conventional approaches are either inefficient or insecure to achieve non-repudiation in electronic commerce. This article presents a practical scheme