Method for authenticating a 1 st consumable or detachable element (20, 300, 300') of a continuous inkjet printer,, comprising: a) - generation, by the controller of the printer, of a 1 st item of random information and the dispatch thereof to an authentication circuit (212, 215) of the 1 st consumable element; b) - encryption of the 1 st item of random information by the authentication circuit of the 1 st consumable element, a 1 st encryption algorithm and a 1 st secret key, thereby forming a 1 st item of encrypted random information, and the dispatch of said item of information to the controller of the printer; c) - encryption of the 1 st item of random information by the controller of the printer and by a 2 nd encryption algorithm, and a 2 nd secret key, thereby forming a 2 nd item of encrypted random information; d) - comparison of, at least the 1 st item of encrypted random information with the 2 nd encrypted item of random information, in order to authenticate the 1 st consumable element, if the 1 st item of encrypted random information and the 2 nd encrypted item of random information are identical, the 1 st encryption algorithm and the 2 nd encryption algorithm being identical, as well as the 1 st secret key and the 2 nd secret key, or to not authenticate the 1 st consumable element, if the 1 st item of encrypted random information and the 2 nd encrypted item of random information are not identical; and after authentication of the 1 st consumable element by the controller: e) - at least one part of a 3 rd key, termed the shared key, is, upon request from the controller, dispatched by the 1 st consumable or detachable element to the continuous inkjet printer, or made available by the 1 st consumable element for being read by the controller of the printer, the last one containing a deciphering algorithm to decipher data with help of the shared key. a) - generation, by the controller of the printer, of a 1 st item of random information and the dispatch thereof to an authentication circuit (212, 215) of the 1 st consumable element; b) - encryption of the 1 st item of random information by the authentication circuit of the 1 st consumable element, a 1 st encryption algorithm and a 1 st secret key, thereby forming a 1 st item of encrypted random information, and the dispatch of said item of information to the controller of the printer; c) - encryption of the 1 st item of random information by the controller of the printer and by a 2 nd encryption algorithm, and a 2 nd secret key, thereby forming a 2 nd item of encrypted random information; d) - comparison of, at least the 1 st item of encrypted random information with the 2 nd encrypted item of random information, in order to authenticate the 1 st consumable element, if the 1 st item of encrypted random information and the 2 nd encrypted item of random information are identical, the 1 st encryption algorithm and the 2 nd encryption algorithm being identical, as well as the 1 st secret key and the 2 nd secret key, or to not authenticate the 1 st consumable element, if the 1 st item of encrypted random information and the 2 nd encrypted item of random information are not identical; and after authentication of the 1 st consumable element by the controller: e) - at least one part of a 3 rd key, termed the shared key, is, upon request from the controller, dispatched by the 1 st consumable or detachable element to the continuous inkjet printer, or made available by the 1 st consumable element for being read by the controller of the printer, the last one containing a deciphering algorithm to decipher data with help of the shared key.