The method involves calculating a current signature (SIGN') of primary values stored in non-volatile memories (14, 15). The current signature is combined with a reference signature (SIGN) previously stored in the nonvolatile memory. The combination result is taken into account in a stage of encryption or decryption algorithm using the primary values, where the primary values are calculated from the secondary values at random quantity. An independent claim is also included for an electronic processing circuit for protection of execution of an encryption or decryption algorithm against introduction of disturbance in an implementing step used for implementing primary values obtained from secondary values stored in a non-volatile memory.