A method and a cryptographic device for encrypting/decrypting an input message by using an algorithm having as entries, said input message, a cryptographic key, and a complementary unique value used as parameter of the algorithm. The output data is formed by the input message decrypted/encrypted by the algorithm using the cryptographic key and the complementary value. The latter is determined on the basis of a unique value physically bound to an electronic device by using a physically unclonable function (PUF) which is inherent to this device and which is used to generate this unique value from a plurality of physical measurements carried out on components integrated in said device.