Patent ID: 7246098

Claim:
A consumable authentication protocol for a printer consumable, the protocol 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 in the trusted authentication chip; applying, in the trusted authentication chip, an asymmetric encrypt function to the original random number using a first key from the trusted authentication chip to produce a first encrypted outcome; passing the first encrypted outcome to the untrusted authentication chip; decrypting, in the untrusted authentication chip, the first encrypted outcome with an asymmetric decrypt function using a second secret key from the untrusted authentication chip to produce a first decrypted outcome; applying, in the untrusted authentication chip, an asymmetric encrypt function to the first decrypted outcome together with an original data message read from the untrusted authentication chip using the second secret key to produce a second encrypted outcome; passing the second encrypted outcome together with the original data message to the trusted authentication chip; decrypting, in the trusted authentication chip, the second encrypted outcome with an asymmetric decrypt function using the first key to produce a decrypted random number and a decrypted data message; comparing the decrypted random number and the decrypted data message with the original random number and the received original data message, 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.