Class coalescence for obfuscation of object-oriented software

• US 7,150,003 B2
• Filed: 11/25/2002
• Issued: 12/12/2006
• Est. Priority Date: 11/25/2002
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Naumovich, Gleb, Yalcin, Ezgi, Sosonkin, Mikhail, Memon, Nasir D., Yu, Hong Heather
• Primary Examiner(s): INGBERG, TODD D
• Application Number:
  US10/305,200
• Publication Number:
  US 20040103404A1
• Time in Patent Office: 1,478 Days
• Field of Search: 717/108, 717/132, 717/126, 713/176, 713/190, 713/194
• US Class Current: 717/108
• CPC Class Codes: G06F 21/14 against software analysis or reverse engineering, e.g. by obfuscation
• CPC Class Codes: G06F 9/4492 Inheritance

Abstract

A method of obfuscating an object-oriented program is provided. A program is provided that is defined in terms of a plurality of classes. Each of the classes has at least one of a field and a method. At least two of the plurality of classes are combined into a combined class. When the at least two classes are combined, at least one field from at least one of the two classes is included in the combined class, and/or at least one method from at least one of the two classes is included in the combined class. After the at least two classes are combined, the program is transmitted.

Claims

1. A method of obfuscating an object-oriented program comprising the steps of:

providing a program defined in terms of a plurality of classes, each of the classes having at least one of a field or a method;

combining at least two of the plurality of classes into a combined class, said step of combining comprising at least one of

(a) including at least one field from at least one of the two classes in the combined class, or

(b) including at least one method from at least one of the two classes in the combined class;

removing the at least two of the plurality of classes from the program; and

storing the program that includes the combined class.

2. The method of claim 1 wherein said step of combining comprises:

including at least one field from each of the at least two classes in the combined class.

3. The method of claim 1 wherein said step of combining comprises:

including at least one method from each of the at least two classes in the combined class.

4. The method of claim 1 wherein said step of combining comprises:

including at least one field from each of the at least two classes in the combined class, and

including at least one method from each of the at least two classes in the combined class.

5. The method of claim 1 additionally comprising the step of:

renaming at least one of a plurality of variables in the combined class in order to further obfuscate the program.

6. The method of claim 1 wherein the program includes an interface implemented by at least one of the at least two classes, the method additionally comprising the step of:

deleting the interface.

7. The method of claim 1 further comprising the step of:

including a watermark in the program.

8. The method of claim 1 wherein at least one of the at least two classes combined is an inner class, and the step of combining includes the step of converting the inner class into a non-inner class.

9. The method of claim 1 wherein at least one of the at least two classes to be combined is an abstract class, and the step of combining includes converting the abstract class into a concrete class.

10. The method of claim 1 additionally comprising the step of:

transmitting the program after said step of combining.

11. A method of obfuscating an object-oriented program comprising the steps of:

copying a first program to provide a second program;

combining a first class and a second class included in the first program to produce a combined class in the second program;

replacing all uses of the first class and the second class in the second program with respective uses of the combined class in the second program;

removing the at least two of the plurality of classes from the program; and

storing the second program that includes the combined class.

12. The method of claim 11 additionally comprising the step of:

renaming references to the first class and the second class with references to the combined class in the second program.

13. The method of claim 11 additionally comprising the step of:

removing the first class and the second class from the second program.

14. The method of claim 11 additionally comprising the step of:

mapping each of a plurality of types included in the first program with a respective type in the second program.

15. The method of claim 11 additionally comprising the step of:

setting a visibility of the combined class in the second program based on the visibility of the first class and the second class in the first program.

16. The method of claim 11 wherein said step of replacing includes:

converting each of a plurality of constructors included in the first class and the second class into a respective constructor in the combined class;

converting each of a plurality of methods included in the first class and the second class into a respective method in the combined class; and

converting each of a plurality of fields included in the first class and the second class into a respective field in the combined class.

17. A method of obfuscating an object-oriented program comprising the steps of:

copying a first program to provide a second program;

combining a first class and a second class included in the first program to produce a combined class in the second program;

mapping each of a plurality of types included in the first program with a respective type in the second program;

replacing all uses of the first class and the second class in the second program with respective uses of the combined class in the second program;

removing the first class and the second class from the second program; and

storing the second program that includes the combined class.

18. A computer readable medium including computer program instructions which cause a computer to implement a method for obfuscating an object-oriented program comprising the steps of:

providing a program defined in terms of a plurality of classes, each of the classes having at least one of a field and a method;

combining at least two of the plurality of classes into a combined class, said step of combining comprising at least one of

(a) including at least one field from at least one of the two classes in the combined class, or

(b) including at least one method from at least one of the two classes in the combined class;

removing the at least two of the plurality of classes from the program; and

storing the program that includes the combined class.

19. A computer readable medium including computer program instructions which cause a computer to implement a method for obfuscating an object-oriented program comprising the steps of:

copying a first program to provide a second program;

combining a first class and a second class included in the first program to produce a combined class in the second program;

placing all uses of the first class and the second class in the second program with respective uses of the combined class in the second program;

removing at least the first and second classes from the program; and

storing the second program that includes the combined class.

20. A computer readable medium including computer program instructions which cause a computer to implement a method for obfuscating an object-oriented program comprising the steps of:

copying a first program to provide a second program;

combining a first class and a second class included in the first program to produce a combined class in the second program;

mapping each of a plurality of types included in the first program with a respective type in the second program;

replacing all uses of the first class and the second class in the second program with respective uses of the combined class in the second program;

removing the first class and the second class from the second program; and

storing the second program that includes the combined class.