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Abstract. First, we introduce the notion of divertibility as a protocol property as opposed to the existing notion as a language property (see Okamoto, Ohta [0090]). We give a definition of protocol divertibility that applies to arbitrary 2-party protocols and is compatible with Okamoto and Ohta's definition in the case of interactive zero-knowledge proofs. Other important examples falling under the new definition are blind signature protocols. We propose a sufficiency criterion for divertibility that is satisfied by many existing protocols and which, surprisingly, generalizes to cover several protocols not normally associated with divertibility (e.g., Diffie-Hellman key exchange). Next, we introduce atomic proxy cryptography, in which an atomic proxy ]unction, in conjunction with a public proxy key, converts ciphertexts (messages or signatures) for one key into ciphertexts for another. Proxy keys, once generated, may be made public and proxy functions applied in untrusted environments. We present atomic proxy functions for discrete-log-based encryption, identification, and signature schemes. It is not clear whether atomic proxy functions exist in general for all public-key cryptosystems. Finally, we discuss the relationship between divertibility and proxy cryptography.

This memo describes version 2 of the KeyNote trust-management system. It specifies the syntax and semantics of KeyNote 'assertions', describes 'action attribute' processing, and outlines the application architecture into which a KeyNote implementation can be fit. The KeyNote architecture and language are useful as building blocks for the trust management aspects of a variety of Internet protocols and services.

Abstract. Existing authorization mechanisms fail to provide powerful and robust tools for handling security at the scale necessary for today's Internet. These mechanisms are coming under increasing strain from the development and deployment of systems that increase the programmability of the Internet. Moreover, this "increased flexibility through programmability" trend seems to be accelerating with the advent of proposals such as Active Networking and Mobile Agents. The trust-management approach to distributed-system security was developed as an answer to the inadequacy of traditional authorization mechanisms. Trust-management engines avoid the need to resolve "identities" in an authorization decision. Instead, they express privileges and restrictions in a programming language. This allows for increased flexibility and expressibility, as well as standardization of modern, scalable security mechanisms. Further advantages of the trust-management approach include proofs that requested transactions comply with local policies and system architectures that encourage developers and administrators to consider an application's security policy carefully and specify it explicitly. In this paper, we examine existing authorization mechanisms and their inadequacies. We introduce the concept of trust management, explain its basic principles, and describe some existing trust-management engines, including PoHcyMaker and KeyNote. We also report on our experience using trust-management engines in several distributed-system applications.

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