Patent ID: 7685424

Claim:
A validation method for determining authenticity of a printer consumable, said validation method including the steps of: providing a printer containing a first authentication chip and a printer consumable containing a second authentication chip; generating a secret random number and calculating a signature for the secret random number using a signature function, in the first chip; encrypting the secret random number and the signature by a symmetric encryption function using a first key, in the first chip; passing the encrypted secret random number and signature from the first chip to the second chip; decrypting, in the second chip, the encrypted secret random number and signature with a symmetric decryption function using the first key; calculating a second signature for the decrypted secret random number using the signature function, in the second chip; comparing, in the second chip, the second signature with the signature decrypted, and in the event that the two signatures match, encrypting, in the second chip, the decrypted secret random number and a memory vector of the second chip by the symmetric encryption function using a second key to produce a first number, the memory vector being comprised of variables holding updatable consumable state data of the printer consumable, the manner of updating the updatable consumable state data being protected by requiring clearing of the memory vector when access to change the updating manner is attempted; calling a test function in the first chip, the test function being called by the first chip receiving the memory vector and the first number from the second chip, the test function including: in the first chip, encrypting the secret random number and the received memory vector by the symmetric encryption function using the second key to produce a second number; in the first chip, comparing the second number with the first number; in the event that the comparison returns a match, considering the second chip to be valid and authorizing use of the printer consumable; and in the event that the comparison returns a mismatch, considering the second chip is invalid and denying use of the printer consumable.