Patent attributes
A method in which a test function is called in a system's internal authentication IC multiple times with a known incorrect value such that, if the internal IC is invalid, an expected invalid response is not generated and, otherwise, the internal IC generates a secret random number and its signature and encrypts these using a first secret key, an external authentication IC connected to the system calls a read function which decrypts the encrypted random number and signature using the first key, calculates the decrypted random number's signature, compares the signatures and upon a match encrypts the decrypted random number and a message of the external IC using a second secret key, the internal IC calls the test function which encrypts the random number and message using the second key, compares the encrypted random numbers and messages, validates the external IC if they match and invalidates the external IC otherwise.
