COMPUTER OBJECT CODE OBFUSCATION USING BOOT INSTALLATION

• US 20090235089A1
• Filed: 03/12/2008
• Published: 09/17/2009
• Est. Priority Date: 03/12/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Farrugia, Augustin J., Lerouge, Julien, CIET, Mathieu
• Granted Patent: US 8,176,337 B2
• Time in Patent Office: Days
• US Class Current: 713/190
• CPC Class Codes: G06F 21/14 against software analysis or reverse engineering, e.g. by obfuscation
• CPC Class Codes: G06F 21/577 Assessing vulnerabilities and evaluating computer system security

Abstract

In the field of computer software, obfuscation techniques for enhancing software security are applied to compiled (object) software code. The obfuscation results here in different versions (instances) of the obfuscated code being provided to different installations (recipient computing devices). The complementary code execution uses a boot loader or boot installer-type program at each installation which contains the requisite logic. Typically, the obfuscation results in a different instance of the obfuscated code for each intended installation (recipient) but each instance being semantically equivalent to the others. This is accomplished in one version by generating a random value or other parameter during the obfuscation process, and using the value to select a particular version of the obfuscating process, and then communicating the value along with boot loader or installer program software. This boot loader then selects which particular process to use for the code execution at the time of installation in accordance with the value. This results in different versions of the obfuscated code being provided to each recipient installation, which further enhances security of the code against reverse engineering by hackers.

Claims

1. A method of protecting computer program code, comprising the acts of:

providing a file of computer program source code;

compiling the file of source code into compiled code; and

obfuscating the compiled code, wherein the obfuscated code is adapted to be executed by a boot installer program upon installation of the code.

2. The method of claim 1, further comprising the act of masking the obfuscated code.

3. The method of claim 1, wherein the obfuscated code when executed is equivalent but not identical to the compiled code.

4. The method of claim 1, further comprising the acts of:

generating a random number;

providing a plurality of obfuscation processes;

selecting one of the processes for the act of obfuscating based on the random number; and

associating the random number with the obfuscated code.

5. The method of claim 1, further comprising the acts of:

providing a plurality of obfuscation processes; and

selecting one of the processes based on a characteristic of a target device.

6. The method of claim 1, wherein the act of obfuscating includes:

providing a plurality of obfuscation processes; and

selecting one of the processes for the act of obfuscating.

7. The method of claim 4, wherein the processes are each a different order for performing a plurality of functions in the compiled code, and wherein the random number determines the particular order.

8. The method of claim 4, where in the obfuscation processes are each equivalent to one another;

and

further comprising selecting a particular one of the obfuscation processes for each instance of the obfuscated code using the value of the random number, wherein each such instance uses a different one of the processes.

9. The method of claim 8, wherein the processes are each one of a Montgomery multiplication, a Quisquater multiplication, and a Barrett multiplication.

10. The method of claim 9, wherein a plurality of Montgomery multiplication processes are provided, using coarsely integrated operand scanning and one using finely integrated operand scanning.

11. The method of claim 10, wherein a plurality of coarsely integrated operand scanning processes are provided, each having a base value of a different length.

12. A method of using protected computer code, comprising the acts of:

providing a file of protected computer compiled code;

providing a boot installer program;

installing the file on a computer memory using the boot installer program, wherein the boot installer program allows execution of the protected file upon installation so it can be executed.

13. The method of claim 12, further comprising the act of unmasking the protected code.

14. The method of claim 12, wherein the protected code when deobfuscated is equivalent but not identical to the protected code before it was obfuscated compiled.

15. The method of claim 12, further comprising the acts of:

providing a random number with the protected code;

providing a plurality of execution processes; and

selecting one of the processes for executing the protected code based on the random number.

16. The method of claim 12, further comprising the acts of:

providing a plurality of execution processes; and

selecting one of the processes based on a characteristic of a target device.

17. The method of claim 12, wherein the act of executing includes:

providing a plurality of processes; and

selecting one of the processes for the execution.

18. The method of claim 16, wherein the processes are each a different order for performing a plurality of functions in the compiled code, and wherein the random number determines the particular order.

19. The method of claim 16, where in the processes are each equivalent to one another;

and

further comprising selecting a particular one of the processes for each instance of the protected code using the value of the random number, wherein each such instance uses a different one of the processes.

20. The method of claim 19, wherein the processes are each one of a Montgomery multiplication, a Quisquater multiplication, and a Barrett multiplication.

21. The method of claim 20, wherein a plurality of Montgomery multiplication processes are provided, one using coarsely integrated operand scanning and one finely integrated operand scanning.

22. The method of claim 21, wherein a plurality of coarsely integrated operand scanning processes are provided, each having a base value of a different length.

23. Apparatus for protecting computer code, comprising:

a memory for storing a file of computer program source code;

a compiler coupled to the memory for compiling the source code into compiled code;

an obfuscator coupled to the compiler to output obfuscated code, wherein the obfuscated code is adapted to be executed by a boot installer program upon installation of the code.

24. Apparatus for installing protected computer code in a computer system, comprising:

a first memory for storing a file of protected computer compiled code;

a second memory for storing a boot installer program;

an element coupled to the memories and which executes the boot installer program and thereby allows execution of the stored file upon installation of the file in the computer system, so the file can be executed.