Public cryptographic control unit and system therefor

A universally available, public cryptographic control unit (crypto unit) is used in a cryptographic system shared by multiple independent users. The crypto unit, which is installed as a peripheral device to a general-purpose computer, loads and unloads encrypted security applets into an onboard RAM memory of the crypto unit, where each security applet is run. The crypto unit and the system of which it is a part, provides a secure internal environment in which only pre-approved security applets are granted permission to load and run. The computing environment within the crypto unit is secured by a cryptographic operation center (OPC) which communicates with each crypto unit. The software developer submits a proposed security applet to the OPC prior to distributing a given security applet in order to obtain the necessary permission for the given security applet. Only if all necessary permissions are obtained from the OPC will a given security applet be allowed to load and run in the crypto unit. When a first security applet is finished running, the crypto unit unloads (swaps out) the presently loaded first security applet in encrypted form to the PC hard drive, and loads (swaps in) the next security applet. The cryptographic context of each security applet is preserved in the file stored on the PC hard drive. In such manner, a single crypto unit is shared among a plurality of independent users.