Secure time communication system

Methods and apparatus for a Secure Time Communication System (10) are disclosed. One embodiment of the invention provides secure and non-interactive communication of clock information over an unsecured communications channel. This communication provides perfect forward secrecy, while detecting and blocking message spoofing, message replay, denial of service and cryptographic performance attacks. This mechanism also bounds the effect of message delay manipulation. The mechanism consists of two components, a filtered time encryptor (16) and a filtered time decryptor (28). The filtered time encryptor (16) produces a message in two parts; a time token followed by an encrypted message body. The time token is used as a filter to detect most attacks and to determine the message key.