On the value of threshold signatures

Threshold signature schemes are examples of threshold cryptosystems, as introduced by Desmedt, [4]. The purpose of this paper is to present a rather simple alternative to threshold signatures which raises questions about the value of such schemes, at least when applied to the mobile agent scenario

Multi-agent system security for mobile communication

This thesis investigates security in multi-agent systems for mobile communication. Mobile as well as non-mobile agent technology is addressed. A general security analysis based on properties of agents and multi-agent systems is presented along with an overview of security measures applicable to multi-agent systems, and in particular to mobile agent systems. A security architecture, designed for deployment of agent technology in a mobile communication environment, is presented. The security architecture allows modelling of interactions at all levels within a mobile communication system. This architecture is used as the basis for describing security services and mechanisms for a multi-agent system. It is shown how security mechanisms can be used in an agent system, with emphasis on secure agent communication. Mobile agents are vulnerable to attacks from the hosts on which they are executing. Two methods for dealing with threats posed by malicious hosts to a trading agent are presented. The rst approach uses a threshold scheme and multiple mobile agents to minimise the eect of malicious hosts. The second introduces trusted nodes into the infrastructure. Undetachable signatures have been proposed as a way to limit the damage a malicious host can do by misusing a signature key carried by a mobile agent. This thesis proposes an alternative scheme based on conventional signatures and public key certicates. Threshold signatures can be used in a mobile agent scenario to spread the risk between several agents and thereby overcome the threats posed by individual malicious hosts. An alternative to threshold signatures, based on conventional signatures, achieving comparable security guarantees with potential practical advantages compared to a threshold scheme is proposed in this thesis. Undetachable signatures and threshold signatures are both concepts applicable to mobile agents. This thesis proposes a technique combining the two schemes to achieve undetachable threshold signatures. This thesis denes the concept of certicate translation, which allows an agent to have one certicate translated into another format if so required, and thereby save storage space as well as being able to cope with a certicate format not foreseen at the time the agent was created