GB2173327A

GB2173327A - Copy protecting computer programs

Info

Publication number: GB2173327A
Application number: GB8605985A
Authority: GB
Inventors: David Allan Phillips
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-03-15
Filing date: 1986-03-11
Publication date: 1986-10-08
Also published as: GB8605985D0

Abstract

A computer program recorded on e.g. a magnetic recording medium (disc or cassette tape) is associated with a test program. The record member has a discontinuity, e.g. a patch free of magnetic material. The test program includes instructions to record back on to a section of the record member including the discontinuity, data already loaded onto the computer from the record member. The so recorded data is then replayed and compared with the original data to detect the effect of the discontinuity. If the expected effect is not detected, the computer is disabled from running the program, as by its memory being cleared by the test program. A PROM-and-RAM cartridge may be used instead of a magnetic recording medium. <IMAGE>

Description

SPECIFICATION Copy protecting computer programs This invention relates to protecting computer programmes recorded on a recording medium such as a magnetic tape or disc against unauthorised copying.

Such programmes can be copied by loading them into a computer and saving them on to a fresh tape or disc. Programs can be protected against copying in this way by including within the program instructions disabling the list and save functions of the computer.

Hackers, however, do not find it difficult to bypass such measures. In any event, a cassette tape can be recorded from one cassette recorder on to a fresh tape on another such recorder.

The present invention provides a method for copy protecting computer programs which cannot be circumvented by the above described methods.

The invention comprises a method for copy protecting a computer program recorded on a recording medium comprising recording the program to be protected together with a test program on to a record member which has a discontinuity in the recording medium, the test program including instructions to record back, on to a section of the record member including the said discontinuity, data already read into the computer from the record member, then, when said data has been recorded, to replay that recorded data, said test program then comparing the replayed data with the original data to detect the effect of said discontinuity and, if the expected effect is not detected, to disable the computer from running the protected program.

The program may disable the computer by clearing its memory.

The test program may count data blocks sent for recording and data blocks played back and disables the computer from running the protected program if the two counts are equal.

Where the record member is a tape cassette, the program to be protected and the test program may be recorded on to one track of the tape, and the 'record back' instruction may be preceded by an instruction to turn the cassette to the other track, which includes the discontinuity in the length on which the test recording is to be made. If an attempt is made to copy the tape on to a fresh tape, by whatever method, whether it be by saving from a loaded program or by tapeto-tape copying, the fresh tape will not have the discontinuity, or, if it has a discontinuity deliberately effected in an attempt to overcome the copy protection, it will not generally be in the right place or of the correct length.

Additional complication can be had by providing multiple discontinuities.

The discontinuities can be provided on specially manufactured tapes or can be applied to regular tapes by dissolving away the magnetic medium or by splicing.

When the record member comprises a disc, the recording back and replaying steps may be effected automatically under the control of the test program.

Embodiments of methods for copy protecting computer programs and of record members for carrying such copy protected programs according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a flow chart, Figure 2 is an illustration of a section of magnetic tape showing the position of data blocks in relation to a discontinuity, Figure 3 is an illustration of another section of magnetic tape showing a different configuration of discontinuity, and Figure 4 is an illustration of a disc showing a discontinuity.

The drawings illustrate a method for copy protecting a computer program recorded on a recording medium-magnetic material on tape 21, Figure 2, or tape 31, Figure 3, or disc 41, Figure 4~comprising recording the program to be protected together with a test programme on to a record member-the tape or disc - which has a discontinuity-gaps 22, 32 in tapes 21, 31 and gap 42 in disc 41~the test program (recorded with the protected program on to sections 23, 33 of tapes 21, 31 and section 43 of disc 41) including instructions to record back, on to the record member (21, 31, 41) data already read into the computer from the record member. This data may comprise sections of the computer program being protected and/or of the test program itself.The instructions are to record the data back on to a section of the record member which includes the discontinuity 22, 32, 41. The instructions are then to replay that recorded data. The test program compares the replayed data with the original data to detect the effect of the discontinuity.

If the expected effect is not detected, the test program disables the computer from running the protected program.

A typical flow chart for the control program is shown in Figure 1, which is intended for a tape recorded program. After the protected program and the test program have been loaded, the test program displays a user instruction to run the tape to the end, then turn it over to record on the other track. The recorder must be switched to PLAY AND RE CORD and the computer now starts SAVEing data blocks already loaded from the protected program and/or the test program over a section of tape that includes the discontinuity.

(Either the test program or the protected program may be recorded first on the tape-it matters not which). Either the whole of one or both programs may be re-recorded on the discontinuity-containing section or only so much of either or both as is necessary to encompass the discontinuity, SAVEing being discontinued by an END OF FILE marker at some point in one or other program.

At this point, the test program displays an instruction to rewind the tape and play back the rewound tape. The test program now verifies each data block and counts the number properly recorded. This number will be less than the number of blocks for which SAVEing was attempted by a number N which depends on the length of the discontinuity.

The test program contains instructions to run the program if the number N is the number expected from the known length of the discontinuity, but to clear the memory of the computer otherwise.

The member N will be the wrong number, of course, if the programme is recorded on to a regular tape without a discontinuity or with a discontinuity which does not correspond precisely to the discontinuity on the original tape.

The arrangements will be similar in the case of a disc except that the disc will not be turned over and the recording and reading operations can be carried out completely automatically under the control of the test program via the disc operating system.

Other possible arrangements will be apparent to the expert, which might involve recording media other than magnetic. For example, a program stored in a PROM cartridge may be protected by incorporating in the cartridge a RAM section which has a discontinuity, the test program writing blocks of data to the RAM section and reading them back to compare them with the blocks already loaded.

Claims

1. A method for copy protecting a computer program recorded on a recording medium comprising recording the program to be protected together with a test program on to a record member which has a discontinuity in the recording medium, the test program including instructions to record back, on to a section of the record member including the said discontinuity, data already read into the computer from the record member, then, when said data has been recorded, to replay that recorded data, said test program then comparing the replayed data with the original data to detect the effect of said discontinuity and, if the expected effect is not detected, to disable the computer from running the protected program.

2. A method according to claim 1, in which the test program disables the computer by clearing its memory.

3. A method according to claim 1 or claim 2, in which the test program counts data blocks sent for recording and data blocks played back and disables the computer from running the protected program if the two counts are equal.

4. A method according to any one of claims 1 to 3, in which the recording medium is magnetic.

5. A method according to claim 4, in which the record member is a tape.

6. A method according to claim 5, in which the program to be protected and the test program are recorded on one track of a cassette tape, the 'record back' instruction being preceded by an instruction to turn the cassette to the other track, said other track including said discontinuity in the length on which the test recording is to be made.

7. A method according to claim 4, in which the record member is a disc.

8. A method according to claim 7, in which the recording back and replaying steps are effected automatically under the control of the test program.

9. A method according to any one of claims 4 to 8, in which the discontinuity comprises an absence of magnetic medium.

10. A method for copy protecting a computer program substantially as hereinbefore described with reference to the accompanying drawings.

11. A record member for recording a computer program copy protected according to any one of claims 1 to 10, comprising a discontinuity in the recording medium.

12. A record member according to claim 11, being a cassette tape.

13. A record member according to claim 11, being a magnetic disc.

14. A record member according to any one of claims 11 to 13, having a copy protected computer program and a test program recorded thereon.

15. A record member substantially as hereinbefore described with reference to the accompanying drawings.