This document establishes a method of encrypting certain elements of the ALERT-C coded data carried in the RDS-TMC type 8A data group, such that without application by a terminal or receiver of an appropriate key, the information conveyed is virtually worthless.
Before a terminal is able to decrypt the data, the terminal requires two "keys". The first is given in confidence by the service provider to terminal manufacturers with whom they have a commercial relationship; the second is broadcast in the "Encryption Administration Group," which is also a type 8A group. This International Standard explains the purpose of the two keys and how often and when the transmitted key may be changed.
Before an individual terminal may present decrypted messages to the end-user, it must have been activated to do so. Activation requires that a PIN code be entered. The PIN code controls access rights to each service and subscription period, allowing both lifetime and term business models to co-exist.
The International Standard also describes the considerations for service providers wishing to introduce an encrypted RDS-TMC service, migrating from either a "free-to-air" service based on public "Location Tables" or a commercial service based on a proprietary Location Table.
Finally, "hooks" have been left in the bit allocation of the type 8A group to allow extension of encryption to other RDS-TMC services.