1. A method of protecting an integrity of a data processing system, the method comprising: determining a data string to be protected, an integrity of the data string being an indication of the integrity of the data processing system, the data processing system processing data according to a cryptographic algorithm; computing a network of look-up tables for implementing the cryptographic algorithm including a cryptographic key using a redundancy in the look-up tables so that the data string is incorporated into two or more of the look-up tables; and enabling the system to process the data using the network of look-up tables, wherein a change of the data string in the network of look-up tables causes the system to lose its capability to process the data according to the data processing function.