Secure messaging systems

Abstract

A secure communication system wherein encrypted messages are passed between selected pairs of user terminals in a secure messaging system. A link is first established between the two terminals of the pair, one terminal sending a request to a key distribution center (KDC), which then provides encrypting keys to both terminals so they can communicate with each other. (Messages involving the KDC are themselves protected by encryption). The keys sent out by the KDC are key transporting keys, which are used by the terminals solely to transport data transporting keys between each other. The data transporting keys are used to transport (encrypt) the actual messages, and for security are changed after a usage count is reached; a fresh data transporting key is then generated and transferred under the key transporting key. This minimizes the load on the KDC. A hierarchy or key transporting keys can be used. The KDC (but not the user terminals) maintains a log to enable recover after a system failure. A journey key can be generated to allow a user temporary access to a link from a third terminal.

Dependencies are inferred from the claim text.