Method of setting up electrical communications between an imaging device and a supply item

A method of setting up electrical communications between an imaging device and a supply item configured for installation in the imaging device using an inter-integrated circuit communications bus, the imaging device having a controller and a first chip in communication with each other and the supply item having a second chip configured to electrically communicate therewith, comprising:

• providing the second chip of the supply item with a memory storing therein a device certificate identifying the second chip;
• configuring the second chip of the supply item to receive one or more requests for the device certificate from the imaging device;
• configuring the second chip of the supply item to provide to the imaging device both an unencrypted and encrypted instance of the device certificate;
• configuring the second chip of the supply item to receive a device certificate of the first chip of the imaging device;
• and
• exchanging encryption keys between the first and second chips,
• wherein the device certificate of the second chip of the supply item includes a device unique public key signed by a global key along with serial or part numbers of the chip and unique signatures.