Patent ID: 7346586

Claim:
A validation protocol for a printer consumable comprising the steps of: providing a printer containing a trusted authentication chip and a printer consumable containing an untrusted authentication chip; generating an original random number; applying, in the trusted authentication chip, an asymmetric encryption function to the random number using a first key from the trusted authentication chip to produce an encrypted random number; passing the encrypted random number to the untrusted authentication chip; decrypting, in he untrusted authentication chip, the encrypted random number with an asymmetric decryption function using a second secret key from the untrusted authentication chip to produce a decrypted random number; comparing the decrypted random number with the original random number, without knowledge of the second secret key, and in the event of a match considering the printer consumable to be valid and allowing the consumption of the consumable by the printer; and, otherwise considering the printer consumable to be invalid and thereby restricting the consumption of the printer consumable by the printer.