Patent ID: 8195955

Claim:
A method for cryptographic authentication in an access security system, the method comprising: incrementing consecutive counts in segments of an Electrically Erasable Programmable Read-Only Memory (EEPROM) by; retrieving an invalid count in one of three EEPROM segments; detecting a maximum valid count from two remaining valid counts if an invalid count exists; overwriting the invalid count with the maximum valid count; when no invalid count exists, detecting a smallest valid count from three valid counts, wherein detecting the smallest valid count follows the retrieving step; detecting a largest valid count from the three valid counts; and overwriting the smallest valid count with the largest valid count, wherein the cryptographic authentication occurs after each successful execution of the incrementing step; and after each incrementation, updating a current count in not more than one EEPROM segment to produce an updated counter value; and using each updated counter value as a changing initialization value in subsequent cryptographic authentications.