These slides discusses the checks to be built in to ensure that covert channels and Trojan code do not exist in the software.
A covert channel can expose information by some indirect and obscure means. It may be activated by changing a parameter by both secure and insecure elements of a computing system, or by embedding information into a data stream. Trojan code is designed to affect a system in a way that is not authorised and not readily noticed and not required by the recipient or user of the program. Covert channels and Trojan code rarely occur by accident. The following controls may take care of the concerns of covert channels and Trojan horse: