A method of authenticating a consumable or detachable element of a continuous inkjet printer comprising: the controller of the printer generating a 1st item of random information that is dispatched to an authentication circuit of the element; encrypting the 1st item of information by the authentication circuit using a 1st encryption algorithm and a 1st secret key to form a 1st item of encrypted random information; dispatching the 1st item of information to the controller; encrypting the 1st item of information by the controller using a 2nd encryption algorithm and a 2nd secret key to form a 2nd item of encrypted random information; comparing the 1st item of encrypted random information with the 2nd encrypted item of random information to authenticate the consumable element; and if the consumable element is authenticated, dispatching at least one part of a 3rd key, termed the shared key, by the element to the printer.