1. A computer system comprising computer readable media for establishing and utilizing a secure communication channel between repositories for conducting a usage transaction of a digital work, said computer readable media having encoded thereon: an identification certificate of a repository certified by a master repository; an external interface of said repository programmed to establish the secure communication channel using a session initiation transaction protocol, the session initiation transaction protocol including: receiving, at another repository, a registration message, the registration message including the identification certificate of said repository and a registration identifier, validating, at the another repository, the authenticity of said repository by verifying the identification certificate, generating a message to test the authenticity of said repository, sending the generated message to said repository, and verifying if said repository correctly processed the generated message, and exchanging messages including at least one session key between said repository and the another repository, wherein the session key is to be used in communications during a session between said repository and the another repository, said external interface also being programmed to conduct a secure transaction with the another repository, including receiving the digital work; and a processor programmed to conduct the usage transaction, wherein the usage transaction comprises controlling use of the digital work in accordance with usage rights associated with the digital work.