A method for securely encoding and transmitting a message by an originating device to one of a plurality of recipient devices, said message being associated with a particular one of a plurality of application running on the originating device. Transmission is generated by using a device identifier, an application identifier and an application value, of a message value; combining the message value with one or more first secret values, said secret values being known substantially only to the originating device and one or more intended recipient device of the message, to establish a secret message value; applying the secret message value and the message to an encoding process to form a secure message block, and combining an address with a device identifier, the application identifier, the application value and the secure message block, to form a secure message for transmission which is decodable by the one or more of said intended recipient devices which thereby recover the message, the address, the device identifier, the application identifier and the application value.