1. A communications device for communicating within a communications network, comprising: an initialisation-vector generator that generates, for each of a plurality of outgoing messages, a respective initialisation vector based at least in part on a respective random component, a transmitter address of the communications device, a packet number, and a block number, wherein the packet number is distinct from the block number; and an encryption device that encrypts each of the plurality of outgoing messages based at least in part on a code and the respective initialisation vector.