Discrete Optimisation and Fast Correlation Attacks

Modifications to fast correlation attacks on stream ciphers are investigated. Improvements are achieved with both deterministic and random choices for updates of the corresponding posterior probabilities and with fast and partial resetting methods. The use of simulated annealing and appropriate optimisation heuristics is also proposed and successful experimental results are obtained. It is shown that a search for error-free information sets is a necessary technique to be applied after the iterative error-correction algorithms to deal with high noise probabilities.