Re: A scheme of software protection

From: Matt Mahoney (matmahoney_at_yahoo.com)
Date: 07/11/05 

Date: 11 Jul 2005 11:20:39 -0700

JiXian Yang wrote:
> Jan Panteltje wrote:
> > Do I understand you build a virtual (soft) CPU with a differrent
> > instruction set?
> > That thing can be disassembled, and and then a debugger and disassembler
> > written for it.
>
> Thank you very much for your reply.
>
> Some contents should be added to the paper when I found some reference
> citations.
> Suppose that there exist the debugger and disassembler and the
> instruction set is not differrent, the effect might be:
>
> ...
> Instruction_n;
> Call Calculate_Offset_and_Jump;
> Instruction_n+1;
> Call Calculate_Offset_and_Jump;
> Instruction_n+2;
> Call Calculate_Offset_and_Jump;
> ...
>
> Thanks again for you time.
>
> Sincerely,
>
> JiXian Yang

What is to stop an adversary from writing a virtual CPU with a
debugger, finding the critical jump instruction, then modifying the
virtual CPU to jump the other way at this point?

Do you have an implementation for us to try to break?

-- Matt Mahoney

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