An extra field, the authentication tail, is added to the end of each telecommand data block. The authentication tail contains a counter and a "signature" to guarantee that the command is genuine. The signature is a complex function of a secret key, the counter and the telecommand data.
The telecommand data itself is not encrypted.
Our product range includes support for Telecommand Authentication, based on the ESA Telecommand Authentication Unit (AU), which is an ESA extension to the standard CCSDS Packet Telecommand Architecture. The Authentication Unit Shell package is a software component which implements all the features of the ground and space ends of the AU. The Telecommand Encoder Shell and Telecommand Decoder Shell packages provide optional support for the AU.
AU Features
AU Shell
TC Encoder Shell
TC Decoder Shell