Patent ID: 7526648

Claim:
A symmetric cryptographic method of protecting a hardwired chip against fraud in transactions between an application and the hardwired chip, the method comprising: calculating a certificate (S) from input parameters (E m ) in the hardwired chip, wherein one of the input parameters (E m ) is a secret key K stored in a protected memory area of the hardwired chip and another of the input parameters (E m ) is a die (R) external to the hardwired chip, the die being generated and supplied to the hardwired chip by the application before executing the method; mixing some or all of the input parameters (E m ) by means of a mixing function and supplying a mixing function output data item E′=(e′ 1 , e′ 2 , . . . , e′ n , . . . , e′ N ); changing the state of a finite state automaton from an old state to a new state in accordance with a function dependent on at least the old state and a value from the series of bits (e′ 1 , e′ 2 , . . . , e′ n , . . . , e′ N ); and calculating the certificate (S) by means of an output function having at least one state of the automaton as an input argument.