Re: [Qemu-devel] QEMU as a "virtual smart card"?

[Paul Brook <paul@codesourcery.com>]

> Assume that I wanted to protect a secret algorithm in some C program.

You're never going to be able to do this. At best you're going to add a few 
levels of obfuscation. At worst you're going to give yourself a false sense of 
security, while actually making it easier to defeat.

The reason the Windows DRM stuff works is because it's protected by the lowest 
level of the OS/hardware, and that protection extends up the whole software 
stack. As soon as you loose this link (e.g. by running inside a virtual 
machine, or as a userspace application without host kernel magic) then you're 
vulnerable to anyone with a copy of gdb.

The whole point of a smartcard is that it's a black box where you can't 
observe its operation at all, only its output.

> Normally this is compiled into the machine code of a certain processor
> and there are standard tools (disassembler, debugger) that can be used
> to figure out what the secret algorithm does.

> A virtual machine has a virtual processor.  Assume now that I was to
> shuffle around machine instructions both in the processor of the
> virtual machine and in the back-end of my c-compiler.  I imagine that
> it would be possible to automate this process (some refactoring tool?)
> and to do some random shuffling.

This is no different from a simple bytecoded execution engine, and fairly 
straightforward to reverse-engineer. An experienced hacker will have no 
problem writing their own reverse engineering tools to strip away your 
obfuscation. Remember that your "encryption" is still native host code, with 
any keys plainly visible.

Paul