The coprocessor 15 has some features in common with the Support Hardware of our referenced U.S. Pat. No. 4,644,493. More particularly, the coprocessor provides each software vendor with an instance of a higher privilege level than the user but at the same time does not give any software vendor access to other vendors' privileged information. All application software decrypted and run on the coprocessor is at the lower of the two privilege levels; the higher privilege level, implemented in the ROM resident firmware, controls access to the non-volatile RAM 153, loading, decrypting and running operations. This structure in the coprocessor prevents a software vendor from writing a monitor which would run on the coprocessor to access the firmware and non-volatile memory (including the decryption keys) and make that information available to the host 10. Accordingly, the coprocessor 15 has a first or lower privilege level which has access to the RAM 151; as already described, the RAM 151 is secured from the user and/or the host 10. The first privilege level includes first level operating instructions for executing protected software. The coprocessor 15, however, also has defined a second privilege level including a second level secure memory and second level operating instructions. The second level secure memory is represented by the non-volatile RAM 153 and the second level operating instructions are defined in the ROM 152. The second privilege level is secured both against the user and any software author. It is the second privilege level of the coprocessor 15 which is involved in acquisition of rights to execute and therefore controls the procedures antecedent thereto. The same second privilege level also responds to user requests for execution of protected software, provides for the loading and decryption of protected software and initiating the first privilege level into operation for execution of the protected software, but only in the event that the second privilege level determines that such execution is authorized.