Abstract: A method (600) for operating a constrained device is disclosed, the constrained device being operable to communicate with an entity over a network. The method, performed by the constrained device, comprises generating a message for transmission to the entity (602), encrypting the generated message by applying a Pseudo Random Binary Sequence (PRBS) to the generated message (604), and transmitting the encrypted message to the entity (606). Also disclosed is a method (700) for operating an entity comprising receiving an encrypted message from a constrained device (702) and decrypting the encrypted message by applying a PRBS to the encrypted message. In some examples of the present disclosure, a constrained device and entity may dynamically renew the PRBS used for encryption and decryption of exchanged messages.