the calculation of encryption keys is a processor intensive undertaking that is not suited for “ thin client ” terminal devices typically used for session applications in an internet protocol network . the present invention provides an encryption scheme for use with such terminal devices for the secure transmission of session data that minimizes session set - up delays associated with the exchange of encryption keys . first , keys are negotiated between network elements using prior art techniques . then , security is maintained by refreshing symmetric keys after each session under cover of an existing key . perfect forward security can be provided by “ breaking the chain ” through periodic key refreshes during system idle times .