Modern encryption is based on unproven assumptions concerning the intractability of certain computational tasks. We present a novel encryption method and prove its security against an adversary with unlimited computing power. The encryption remains secure even if the adversary mounts an adaptive attack and later on obtains the secret decryption key. Hence the property of ever lasting secrecy. We shall also discuss general cryptographic issues. The presentation is self contained.

Deduction modulo is a way to express a theory using computation rules instead of axioms. We present in this paper an extension of deduction modulo, called Polarized deduction modulo, where some rules can only be used at positive occurrences, while others can only be used at negative ones. We show that all theories in propositional calculus can be expressed in this framework and that cuts can always be eliminated with such theories.

In this paper we will present various models and techniques for communication in dynamic networks. Dynamic networks are networks of dynamically changing bandwidth or topology. Situations in which dynamic networks occur are, for example: faulty networks (links go up and down), the Internet (the bandwidth of connections may vary), and wireless networks (mobile units move around). We investigate the problem of how to ensure connectivity, how to route, and how to perform admission control in these networks. Some of these problems have already been partly solved, but many problems are still wide open. The aim of this paper is to give an overview of recent results in this area, to identify some the most interesting open problems and to suggest models and techniques that allow to study them.