What is the Universal Services Protocol?
PGP Universal Server 3.0 includes the Universal Services Protocol (USP) which is a new feature for communication between PGP Desktop, PGP Universal Satellite, and keyservers.
The Universal Services Protocol (USP) provides communication between external services and the PGP Key Management Service (KMS). USP enables key management and policy services to clients and other external services.
USP is initially configured with a single interface, on port 443 using SSL, for communication with PGP clients. You can add additional interfaces to allow communication over other ports or via HTTP rather than HTTPS (SSL).
Click here for an article on how to add an interface for USP.