Project-team COSMIQ

Quantum computers are expected to significantly disrupt modern cryptography. We investigate the consequences of quantum computing in several ways. First, we devise quantum attacks on both symmetric and asymmetric cryptographic primitives that are based on adapting well known techniques to the new quantum setting. Second, we create entirely new dedicated quantum algorithms and attacks. Our overall goal is to come up with an extensive quantum cryptanalysis toolbox that would allow a precise evaluation of the security of a cryptographic primitive against quantum computers.

We work on stream ciphers, block ciphers and hash functions. Our investigations consider all aspects of the field, from practical (new attacks, concrete specifications of new systems) to more theoretical ones (study of the algebraic structure of underlying mathematical objects, definition of optimal objects).

Cryptographic primitives which exploit some problems coming from coding theory provide a good alternative to the commonly used systems based on number theory like RSA. They are usually named post-quantum cryptosystems since they would not become obsolete with the coming up of the quantum computer. We investigate the security of these systems, their practical implementation and the design of fast cryptographic primitives based on codes.

The main obstacle towards the development of quantum computing is decoherence, a consequence of the interaction of the computer with a noisy environment. We investigate approaches to quantum error-correction as a way to fight against this effect, and we study more particularly some families of quantum error-correcting codes which generalise the best classical codes available today. Our research also covers quantum cryptography where we study the security of efficient protocols for key distribution, in collaboration with experimental groups. More generally, we investigate how quantum theory severely constraints the action of honest and malicious parties in cryptographic scenarios.