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Design of secure stream ciphers

Final Activity Report Summary - DSSC (Design of secure stream ciphers)

The areas of information security and cryptography are two of the most active and important research areas worldwide. This project focused on cryptography, and especially on a category of cryptographic algorithms, the stream ciphers. The last two years, stream ciphers have attracted the interest of the research community, in part due to the eStream contest organised by the European Network of Excellence ECRYPT. The project, following the initial proposal, had three main goals. The analysis of the characteristics that a stream cipher must possess, the evaluation of existing attacks against stream ciphers and the proposal of new ones, and finally the impression of the fellow's experience and expertise in a new design proposal.

Concerning the first characteristics, the notion of maximum nonlinearity has been study. It consists of an important criterion for measuring the unpredictability and randomness of the stream ciphers output. Both unpredictability and randomness are necessary for the security of a cryptographic algorithm.

In terms of the second objective, the algebraic attacks have been mainly studied. A recently proposed algebraic attack has been evaluated. The evaluation revealed inaccuracies. A new attack was proposed that correct mistakes and works in any all cases.

Finally, a new stream cipher has been proposed. The new design can be applied in the physical layer, encrypting information that is transmitted through optical fibres, and it bases its security on the laws of physics.