A non-transitory computer-readable data storage medium storing computer-executable code executable by a replaceable item for printing devices to perform a method comprising: in response to receiving a request for an identity of the replaceable item from a host device to which the replaceable item has been connected, selecting the identity from a plurality of replaceable item identities stored within the replaceable item, the replaceable item storing a plurality of authentication values for each replaceable item identity; sending the selected identity to the host device; after sending the selected identity, and in response to receiving a request for an authentication value from the host device, determining whether the replaceable item stores the requested authentication value for the selected identity; and in response to determining that the replaceable item stores the requested authentication value for the selected identity, sending the requested authentication value for the selected identity to the host device; characterised in that: selecting the identity from the replaceable item identities stored within the replaceable item comprises: determining whether the replaceable item was previously unsuccessfully authenticated with the host device; and in response to determining that the replaceable item was previously unsuccessfully authenticated with the host device, randomly selecting one of the replaceable item identities that the replaceable item did not send when the replaceable item was previously unsuccessfully authenticated. in response to receiving a request for an identity of the replaceable item from a host device to which the replaceable item has been connected, selecting the identity from a plurality of replaceable item identities stored within the replaceable item, the replaceable item storing a plurality of authentication values for each replaceable item identity; sending the selected identity to the host device; after sending the selected identity, and in response to receiving a request for an authentication value from the host device, determining whether the replaceable item stores the requested authentication value for the selected identity; and in response to determining that the replaceable item stores the requested authentication value for the selected identity, sending the requested authentication value for the selected identity to the host device; characterised in that: selecting the identity from the replaceable item identities stored within the replaceable item comprises: determining whether the replaceable item was previously unsuccessfully authenticated with the host device; and in response to determining that the replaceable item was previously unsuccessfully authenticated with the host device, randomly selecting one of the replaceable item identities that the replaceable item did not send when the replaceable item was previously unsuccessfully authenticated. determining whether the replaceable item was previously unsuccessfully authenticated with the host device; and in response to determining that the replaceable item was previously unsuccessfully authenticated with the host device, randomly selecting one of the replaceable item identities that the replaceable item did not send when the replaceable item was previously unsuccessfully authenticated.