Method and device for enhancing manipulation-proof of critical data

A method for increasing the tamper resistance of critical register data comprises the steps:Loading a codeword, a pointer or MAC associated with a codeword in a first nonvolatile memory (20 or 25) protected against removal and manipulation,Loading a codeword or a MAC formed by means of the codeword into second non-volatile memories (NVM 5a, 5b) to be protected containing the postal register data, the codeword being associated with the last operating status of the franking machine,Checking the validity of the codeword or of the MAC formed by means of the codeword at least at the time of switching on the franking machine and subsequently at least on the basis of a pseudorandom sequence at intervals,Replacing the old codeword with a predetermined new codeword when the processor, after validity checking, acknowledges the validity of the old codeword or the validity of the codeword formed by the codeword orBlocking of the franking machine after the time of turning on the franking machine, if the processor after validation but the validity of the old codeword or the validity of the means of the codeword formed MACs know.