US Patent 7788493 Authenticating users

A method of authenticating a user seeking access to a service from a service provider in a communication network, the method comprising: allocating to a user a plurality of service-specific identities for accessing respective services; issuing a request from the user, the request identifying the service to be accessed and including a public key of the user; at a certification authority, authenticating the request and issuing a public key certificate for binding the service-specific identity with the public key in the request, and returning the public key certificate to the user.