both the end device and the set top box that will help it authenticate its time and position stb denotes the initial receiver ed denotes the end device in denotes the intermediary network ls denotes the location server closest to ed ca denotes a trusted certification authority cert x is a public key certificate for entity x k x y denotes a secret key possessed only by x and y id x denotes the unique id of entity x r x is a random number issued by entity x t i is a time stamp issued at time i dt i j is the time interval between t i and t j dt max is an upper limit on a time interval used to determine how close geographically one device is to another time is the time and date data provided by ls loc is the location data provided by ls e k z is the result of the encipherment of data z with a symmetric algorithm using the key k mac k z is the message authentication code generated by hashing data z with the key k s x z is entity x 39 s private signature transformation operating on data z v x s x z is entity x 39 s public verification transformation operating on x 39 s signature s x z and data z x y is the result of the concatenation of data items.