In cryptography, decorrelation theory is a system developed by Serge Vaudenay in 1998 for designing block ciphers to be provably secure against differential cryptanalysis, linear cryptanalysis, and even undiscovered cryptanalytic attacks meeting certain broad criteria. Ciphers designed using these principles include COCONUT98 and the AES candidate DFC, both of which have been shown to be vulnerable to some forms of cryptanalysis not covered by the theory.