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FRINATEK-Fri prosj.st. mat.,naturv.,tek

Cryptographic Boolean Functions for Threshold Implementations

Alternative title: Kryptografiske boolske funksjoner for terskelimplementasjoner

Awarded: NOK 10.5 mill.

Cryptographic ciphers serve the very important function of securing our every day communication and data against unauthorised access. They are in use everywhere: web-browsers, mobile phones, payment cards, tv-decoders, smart cards, etc. The fact that more and more of them are now run in embedded devices makes the rather recent side channel attacks (SCA) a huge threat: unwanted information leakage during the execution of the algorithms can potentially compromise their security. Cryptosystems for which the best known classical attacks would need millennia to extract the private key have their implementation broken in a few seconds by SCA if they do not include countermeasures. The design of such countermeasures which would not extend too much the silicon area is therefore a prominent task nowadays. This is a challenge since they need to be safe to use not only today, but also in the coming years. The aim of this project is to find new criteria for cryptographic functions that will provide resistance simultaneously against mathematical cryptanalysis and SCA. For the latter case the focus will be on threshold implementations that have recently been proposed as a countermeasure against SCA.

Cryptographic ciphers serve the very important function of securing our every day communication and data against unauthorised access. They are in use everywhere: web-browsers, mobile phones, payment cards, tv-decoders, smart cards, etc. The fact that more and more of them are now run in embedded devices makes the rather recent side channel attacks (SCA) a huge threat: unwanted information leakage during the execution of the algorithms can potentially compromise their security. Cryptosystems for which the best known classical attacks would need millennia to extract the private key have their implementation broken in a few seconds by SCA if they do not include countermeasures. The design of such countermeasures which would not extend too much the silicon area is therefore a prominent task nowadays. This is a challenge since they need to be safe to use not only today, but also in the coming years. The present project deals with those Boolean functions that are used as S-boxes in block ciphers, within the context of Threshold Implementations (TI). The principle of TI is to design S-boxes in such a way as to allow "natural" resistance against SCA without the need to include too much randomness into the implementation of a cryptosystem. Then these implementations consolidate the resilience of cryptographic primitives against cryptanalytic attacks on their hardware implementations, while ensuring the minimization of the silicon area. The idea is appealing but much remains to be done in this matter, both to transform the S-boxes used in existing cryptosystems and to design others from scratch. Our plan is to study Boolean functions and address these problems with the ultimate aim of being able to provide constructions offering assured future-proof security that are also efficient in hardware. This needs competences in both Boolean functions and SCA, and we think such hard-to-find skills come together in this project team.

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FRINATEK-Fri prosj.st. mat.,naturv.,tek