Method of authenticating printer consumable

Abstract

A method for authenticating a printer consumable in which an encrypted random number and its first signature are passed from a printer authentication chip to a consumable authentication chip, in the consumable chip: the encrypted random number and first signature are decrypted; a second signature of the random number is calculated and compared with the first signature to produce a match at which a first number produced by encrypting the random number and a memory vector is passed to the printer chip, and in the printer chip, a second number is produced by encrypting the random number and memory vector and compared with the first number to produce a match and valid consumable chip, or a mismatch and invalid consumable chip. The memory vector comprises updatable consumable state data whose manner of updating is protected by requiring clearing of the memory vector when change of the updating manner is attempted.

1 . A method for authenticating a printer consumable comprising the steps of:
 passing, from an authentication chip of the printer to an authentication chip of the consumable, an encrypted random number and first signature of the random number;   decrypting, in the consumable chip, the encrypted random number and first signature;   calculating, in the consumable chip, a second signature of the decrypted random number;   comparing, in the consumable chip, the first and second signatures and if the compared signatures match, passing, from the consumable chip to the printer chip, a first number produced by encrypting the random number and a memory vector of the consumable chip, the memory vector being comprised of variables holding updatable consumable state data of the 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;   encrypting, in the printer chip, the random number and memory vector to produce a second number;   comparing, in the printer chip, the first and second numbers and if the comparison returns a match, considering the consumable chip valid, and if the comparison returns a mismatch, considering the consumable chip invalid.   
   
   
       2 . A method according to  claim 1 , where the first and second signatures are digital signatures of 160 bits. 
   
   
       3 . A method according to  claim 1 , where the time taken to return an indication the consumable chip is invalid is the same for all bad inputs, and the time taken to return an indication the consumable chip is valid is the same for all good inputs.