Patent ID: 7454617

Claim:
An apparatus for validating the presence of an authorized consumable unit of a printing device, the consumable unit having a first authentication integrated circuit that is configured to store a secret key K A and data on a printing consumable of the consumable unit, the apparatus comprising: a second integrated circuit which stores a public key K T and is configured to hold a random number function which returns random number R, the second integrated circuit being configured to apply a function F[R] to return F KT [R], based on the public key K T , and the first integrated circuit being configured to apply a function D[F KT [R]] to return D KA [F KT [R]], based on the secret key K A ; and a control system which is configured to request F KT [R] from the second integrated circuit, to request D KA [F KT [R]] from the first integrated circuit to obtain R A , and to compare R return by the second integrated circuit with R A returned by the first integrated circuit.