Regine Endsuleit

Attacking a polynomial-based cryptosystem: Polly Cracker

Abstract.We describe several attacks on Polly Cracker, a public key cryptosystem proposed by Fellows and Koblitz. The first kind of attack shows that variations in the CPU time needed for evaluating polynomials can leak significant information about the secret key. This kind of attack might also be of interest when dealing with other cryptosystems using polynomial evaluations, like Patarin’s hidden fields equations.Next, we exhibit some “structural” weaknesses in Polly Cracker’s encryption procedure. In particular, we demonstrate that with the parameters considered in a book by Koblitz it is often possible to reveal the private key easily.

A Liberal Approach to Openness in Societies of Agents.

We outline a model for a society of agents based upon one of the classical theories of sociology: The Webers model. We first investigate its links to agent technology through its relationship with the modeling of micro economy and the concept of expected utility. Then, some of the features of an agent society are enhanced by imposing security and validation requirements. We show that a societal concept from Sociology can be implemented through methods of Computer Science and thus is made feasible.

Censorship-resistant and anonymous P2P filesharing

We present a P2P filesharing system that allows redundant storage of shared files in a way that no participating server ever stores data that could compromise its operator. Instead, only fragments that do not contain any information about the original file in the information theoretic sense are uploaded. Reconstruction of a file requires all fragments it has been decomposed into. By this, in conjunction with other cryptographic methods, we yield significant legal advantages for server operators, as well as censorship-resistance, anonymity, secure routing, authenticated file update and integrity checks.

Agent Alliances: A Means for Practical Threshold Signature

Endsuleit and Mie (2003) have proposed a model for the robust and private evaluation of a function within a group of cooperating mobile agents, called an agent alliance. The model has been given abstractly and is based on a cryptographic protocol for secure multi-party computation. This paper aims on the investigation of the complexity of a threshold signature performed within the alliance model. The goal is to achieve a practical security model in which agents can be allowed to act fully autonomously in their users name without relying on a trusted authority

Introducing robust and private computation into grid technology

We propose to adapt the recently published model for secure multiagent computation (R. Endsuleit et al., 2003) to grid technology. Since the model is based on a protocol for secure multiparty computation we achieve computations that are robust against a (user-defined) maximum number of wrong or missing inputs. Furthermore, all computations and data stay private until they are returned to their originator. Being able to use mobile agents in a per se nontrusted environment like a grid opens up a variety of possibilities for sensitive applications.