Transmission format for protecting privacy of satellite telecontrol - uses information in preamble to access satellite memory for decoding and authenticating message

摘要

The identifying preamble to a transmitted word contains a secret key number which permits selection in the satellite memory of the secret key to be used for the decoding process. The preamble also contains the message number which changes for each message and also the length of the message. The authentification sequence is calculated from the secret key and message number and will change for each message. The octets containing a command such as for steering or switching equipment are accompanied by a cryptogram containing the same command configured with an algorithm dependent on the secret key, message number and the order of the command. On reception this data determines the decoding algorithm and after decoding, the cryptogram phrase is compared with the control phrase. If there is any difference the message is rejected.