Software protection methods and apparatus

• US 4,525,599 A
• Filed: 05/21/1982
• Issued: 06/25/1985
• Est. Priority Date: 05/21/1982
• Status: Expired due to Term

• Current Assignee: General Computer Corp. (GenCC Holding Corp)
• Original Assignee: General Computer Corp. (GenCC Holding Corp)
• Inventors: Curran, Kevin G., Rode, Christian S., Golson, Steven E.
• Primary Examiner(s): Cangialosi, Sal
• Application Number:
  US06/380,771
• Time in Patent Office: 1,131 Days
• Field of Search: 178/22.05, 178/22.08, 178/22.09, 364/200, 364/900, 340/825.34
• US Class Current: 713/190
• CPC Class Codes: G06F 12/1408 by using cryptography for digital transmission H04L9/00
• CPC Class Codes: G06F 21/10 Protecting distributed programs or content, e.g. vending or licensing of copyrighted material protection in video systems or pay television H04N7/16 ; Digital rights management [DRM]
• CPC Class Codes: G06F 21/80 in storage media based on magnetic or optical technology, e.g. disks with sectors preventing unauthorised reproduction or copying of disc-type recordable media G11B20/00
• CPC Class Codes: G06F 21/85 interconnection devices, e.g. bus-connected or in-line devices
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload

Abstract

Methods and apparatus are disclosed for inhibiting the unauthorized copying of ROM-resident computer software or the like, for example, the audio-visual display of an electronic video game. A protection circuit including encryption/decryption means is coupled between the microprocessor and the ROM-memory and is operable in a first mode to properly encrypt/decrypt the program information according to a first algorithm and in a second mode to prevent proper encryption/decryption. The address-data buses are monitored by the protection circuit to detect an invalid program event, such as may occur when a microprocessor emulator is used to attempt an unauthorized copying or "dumping" of the program information. Upon detection of the invalid program event or "trap condition", the protection circuit switches to its second operating mode thereby to prevent copying of the decrypted program information.

Claims

1. The method of inhibiting the unauthorized copying of computer software comprising the steps of:

(a) storing digital program information in preselected address locations of a memory means in an encrypted form according to a first predetermined algorithm;

(b) providing a computer processor for performing preselected functions only in response to the decrypted program information stored in said memory means;

(c) coupling the address and data buses of said computer processor to said memory means through an encryption/decryption means selectively operable in a first mode to encrypt/decrypt said program information according to said first predetermined algorithm and in a second mode to prevent the encryption/decryption of said program information according to said first predetermined algorithm;

(d) monitoring at least one of the address and data buses to detect trap address information, said trap address information being signified by an attempted accessing of the memory means by an operation not occurring during normal execution of the computer program; and

(e) switching said encryption/decryption means from said first operating mode to said second operating mode if a trap address is detected by said monitoring means.

2. The method according to claim 1 in which said second operating mode comprises a second predetermined algorithm.

3. The method of claim 1 including the step of designating as trap address information the attempted accessing of certain address locations in said memory means which are not asserted during normal operation of the computer system.

4. The method of claim 1 including the step of designating as trap address information the assertion of a sequence of program address locations that are not asserted in said sequence during normal program operation.

5. The method of claim 1 in which said coupling step includes coupling said computer processor to said memory means through at least two parallel encoding/decoding circuits, only one of which circuits is operable at a time and only one of which circuits is operable according to said first predetermined algorithm.

6. The method of claim 1 including the further step of selectively resetting said encryption/decryption means to said first operating mode in response to a predetermined reset signal.

7. The method of claim 1 in which said switching step includes latching said encryption/decryption means in said second operating mode in response to momentary detection of said trap address.

8. In a computer system including a central processor for performing preselected functions in response to digital program information stored in encrypted form in a memory means, and communicated between said central processor and said memory means on address and data buses, the improvement comprising:

(a) encryption/decryption means, coupled between said central processor and said memory means, selectively operable in a first mode for encrypting/decrypting said program information according to a first predetermined algorithm and in a second mode according to a second predetermined algorithm for preventing the encryption/decrypting of said program information according to said first predetermined algorithm;

(b) detection means for monitoring at least one of said address and data buses to detect the attempted accessing of the memory means by an operation not occurring during normal execution of the computer program; and

(c) switching means for shifting said encryption/decryption means from said first operating mode to said second operating mode in response to detection of said invalid program event.

9. The improvement of claim 8 in which said encryption/decryption means includes parallel encoding/decoding circuits for, respectively, encrypting/decrypting said program information in response to said first and second predetermined algorithms.

10. The improvement of claim 9 in which said detection means includes circuit means for developing an output signal in response to an invalid program event.

11. In the computer system of claim 8, wherein the detection means for monitoring at least one of said address and data buses includes means for detecting the attempted accessing of certain address locations in said memory means which are not asserted during normal operation of the computer program.

12. The computer system of claim 8, wherein the detection means for monitoring at least one of said address and data buses includes means for detecting the assertion of a sequence of program address locations that are not asserted in said sequence during normal program operation.

13. The improvement of claim 10 in which said switching means includes a state circuit means for maintaining said encryption/decryption means in said second operating mode in response to momentary detection of said invalid program event.

14. The improvement of claim 13 and further including reset means for resetting said encryption/decryption means to said first operating mode.

15. The improvement of claim 8 in which said encryption/decryption means comprises a logic array.

16. The method of inhibiting the unauthorized copying of ROM-resident data constituting the audio-visual display information for an electronic video game comprising the steps of:

(a) storing the audio-visual display information of said electronic video game in encrypted, digital format in a ROM-memory;

(b) providing a microprocessor, display monitor and sound system for generating the audio-visual display of said game in response to the decrypted program information stored in said memory means;

(c) coupling said microprocessor to said ROM-memory through an encryption/decryption means selectively operable in a first mode to encrypt/decrypt said audio-visual display information according to a first predetermined algorithm for presenting said game in decrypted audio-visual format and in a second mode to prevent the encryption/decryption of said display information according to said first predetermined algorithm;

(d) monitoring the digital program information as communicated between said microprocessor and said ROM-memory for identifying an invalid program event, said invalid program event being characterized by the attempted accessing of the memory means by an operation not occurring during normal execution of the computer program; and

(e) switching said encryption/decryption means from said first operating mode to said second operating mode in an invalid program event is detected thereby to prevent copying of the encrypted audio-visual information stored in said ROM-memory.

17. A method for inhibiting the use of a microprocessor emulator to read digital program data stored in memory means in a computer system, comprising the steps of:

(a) storing encrypted digital program data into preselected address locations of memory means;

(b) coupling address and data buses of the microprocessor to the memory means through protection circuit means for encrypting, decrypting and monitoring the addressing of the program data stored in the memory means;

(c) monitoring at least one of the address and data buses to detect an attempted invalid accessing of the memory means, the invalid accessing operation being characterized by an operation not occurring during normal execution of the program; and

(d) returning falsely decrypted program data through the protection circuit means to the microprocessor emulator in response to the detection of the invalid accessing operation.

18. The method of claim 17 wherein the invalid accessing operation comprises the attempted accessing by the microprocessor emulator of address locations in the memory means not preselected for storing the digital program data.

19. The method of claim 17 wherein the invalid accessing operation comprises the assertion of a sequence of program address locations that are not asserted in the same sequence during normal program execution.

20. The method of claim 17 further including the step of operating the protection circuit means in a first mode to provide true decrypted program data from the memory means to a microprocessor in the absence of the detection of an invalid accessing operation.

21. The method of claim 20 wherein the step of returning falsely decrypted program data to the microprocessor emulator includes operating the protection circuit means in a second mode which prevents true decryption of the program data stored in the memory means.

22. The method of claim 21 wherein the step of monitoring at least one of the address and data buses includes generating a switching signal in response to the detection of the invalid accessing operation by the microprocessor emulator to switch the protection circuit means from the first operating mode to the second operating mode.

23. A method for inhibiting the use of a microprocessor emulator to read digital program data stored in memory means in a computer system employing a microprocessor, comprising the step of:

(a) preselecting less than all available address locations in the memory means for storing program data;

(b) storing encrypted microprocessor program data into the preselected address locations of the memory means;

(c) reserving the unselected address locations in the memory means for use in the detection of sequential accessing of the memory means by the microprocessor emulator;

(d) coupling address and data buses of the microprocessor to the memory means through circuit protection means for monitoring the addressing of address locations in the memory means;

(e) monitoring at least one of the address/data buses to detect the accessing by the microprocessor emulator of at least one of the reserved address locations; and

(f) returning false data through the circuit protection means to the microprocessor emulator in response to the detected addressing of any of the reserved address locations in the memory means.

24. The method of claim 23 wherein the step of returning false data to the microprocessor emulator comprises selecting the circuit protection means to invalidity decrypt the encrypted program data before returning the data to the microprocessor emulator.

25. A method for inhibiting the pirating of widely distributed computer software for unauthorized execution on a computer system employing a stock microprocessor, comprising the steps of:

(a) preselecting less than all available address locations in memory means for storing digital program data;

(b) storing digital program data into the preselected address locations in the memory means;

(c) coupling address and data buses of the microprocessor to the memory means through protection circuit means for selectively invalidating the program data;

(d) monitoring the addressing through the protection circuit means of the program data stored in the memory means;

(e) detecting the accessing of other than the preselected address locations in the memory means, thereby indicating an unauthorized attempt to copy the stored program data; and

(f) selecting the protection circuit means to return from the memory means invalid program data in response to the detected unauthorized attempt to copy the stored program.

26. The method of claim 25 further comprising the step of encrypting the digital program data before storing the data to the memory means.

27. The method of claim 26 wherein the step of returning invalid program data through the protection circuit means comprises the step of improperly decrypting the encrypted program stored in the memory means.