Because microcomputers’ usefulness depends on the programs written for them and programmers’ motivation depends on protection of their proprietary interests, software protection is very important. Legal protection such as copyright may suffice for some media, but sad experience has shown that it may afford inadequate protection for microcomputer software.
Many physical schemes for protecting such software have been devised but, as the authors make clear, none of them is secure in the presence of normally available means for reproducing the contents of media on which programs are distributed. The authors’ solution involves a second processor. In A Basic Yorktown Security System (ABYSS), a microcomputer contains a protected processor in which critical segments of each protected program run in a way that cannot be observed from outside. There is much more to the architecture, involving cryptographic protocols that permit backup, relocation, and restrictions on the use of software, but the protected processor is the heart of the scheme.
The paper is well written and covers all technical aspects of the subject thoroughly, aptly, and understandably. Whether the authors’ invention is worth implementing depends on the circumstances. The decision is not a simple matter of pricing a processor, but also involves details of the processor such as what its architecture should be and how it should be attached and packaged; the programming needed for supervisory functions; and the cost of designing and developing protected segments of programs.