我一直在思考如何保护我的C/ c++代码不被反汇编和逆向工程破坏。通常情况下,在我的代码中,我绝不会宽恕这种行为;然而,为了各种人的安全,我目前正在研究的协议决不能被检查或理解。
现在这对我来说是一个新的主题,互联网并没有真正的资源来防止逆向工程,而是描述了大量关于如何逆向工程的信息
到目前为止我想到的一些事情是:
Code injection (calling dummy functions before and after actual function calls)
Code obfustication (mangles the disassembly of the binary)
Write my own startup routines (harder for debuggers to bind to)
void startup();
int _start()
{
startup( );
exit (0)
}
void startup()
{
/* code here */
}
Runtime check for debuggers (and force exit if detected)
Function trampolines
void trampoline(void (*fnptr)(), bool ping = false)
{
if(ping)
fnptr();
else
trampoline(fnptr, true);
}
Pointless allocations and deallocations (stack changes a lot)
Pointless dummy calls and trampolines (tons of jumping in disassembly output)
Tons of casting (for obfuscated disassembly)
我的意思是,这些是我想过的一些事情,但它们都可以在适当的时间框架内由代码分析师解决。我还有别的选择吗?
与大多数人所说的相反,基于他们的直觉和个人经验,我不认为密码安全的程序混淆通常被证明是不可能的。
这是一个完美混淆的程序语句的例子,以证明我的观点:
printf("1677741794\n");
人们永远猜不到它真正的作用是什么
printf("%d\n", 0xBAADF00D ^ 0xDEADBEEF);
关于这个问题有一篇有趣的论文,它证明了一些不可能的结果。它叫做“关于混淆程序的(Im)可能性”。
尽管这篇论文确实证明了使程序与它实现的函数不可区分的混淆是不可能的,但以某种较弱的方式定义的混淆仍然是可能的!
可能最好的选择仍然是使用虚拟化,这引入了另一层需要绕过的间接/混淆,但正如SSpoke在他的回答中所说,这种技术也不是100%安全的。
关键是你不会得到终极保护,因为根本就没有这种东西,即使有,也不会持续太久,这意味着它一开始就不是终极保护。
凡是人组装起来的东西,都可以拆卸。
通常情况下,(正确的)拆卸通常是(一点或更多)更困难的任务,所以你的对手必须更熟练,但你可以假设总有这样的人,这是一个安全的赌注。
如果您希望保护某些内容不受REs的影响,那么您必须至少了解REs使用的常见技术。
这样的话
互联网并不是真正的资源预防逆向工程,而是描述了大量关于如何逆向工程的信息
表现出你的坏态度。我并不是说要使用或嵌入保护,你必须知道如何打破它,但要明智地使用它,你应该知道它的弱点和陷阱。你应该明白这一点。
(有一些软件以错误的方式使用保护,使得这种保护实际上不存在。为了避免含糊,我给你举一个在网上简单描述的例子:牛津英语词典第二版CD-ROM - v4。您可以在以下页面了解SecuROM使用失败的原因:16、32或64位Windows环境下CD-ROM上的牛津英语词典(OED):硬盘安装、错误、字处理宏、网络、字体等)
每件事都需要时间。
如果你是这门学科的新手,没有几个月甚至几年的时间来学习正则表达式,那么就使用其他人提供的可用解决方案。这里的问题很明显,它们已经在那里了,所以你已经知道它们不是100%安全的,但制作自己的新保护只会给你一种被保护的错误感觉,除非你非常了解逆向工程和保护的艺术状态(但你不知道,至少目前不知道)。
软件保护的目的是吓唬新手,拖延常见的正则,并让经验丰富的正则在她/他(希望很有趣)到达应用程序中心后面带微笑。
在商业谈话中,你可能会说这都是为了尽可能地推迟竞争。
(看看Philippe Biondi和Fabrice Desclaux在Black Hat 2006上展示的Skype中的银针)。
你知道有很多关于RE的东西,所以开始阅读吧。:)
我说过虚拟化,所以我将给你一个链接到EXETOOLS论坛的一个示例线程:最佳软件保护:Themida还是Enigma protector ?这可能会对你进一步的搜索有所帮助。
最好的反反汇编技巧,特别是在可变字长指令集上,是在汇编程序/机器代码中,而不是在c中
CLC
BCC over
.byte 0x09
over:
The disassembler has to resolve the problem that a branch destination is the second byte in a multi byte instruction. An instruction set simulator will have no problem though. Branching to computed addresses, which you can cause from C, also make the disassembly difficult to impossible. Instruction set simulator will have no problem with it. Using a simulator to sort out branch destinations for you can aid the disassembly process. Compiled code is relatively clean and easy for a disassembler. So I think some assembly is required.
I think it was near the beginning of Michael Abrash's Zen of Assembly Language where he showed a simple anti disassembler and anti-debugger trick. The 8088/6 had a prefetch queue what you did was have an instruction that modified the next instruction or a couple ahead. If single stepping then you executed the modified instruction, if your instruction set simulator did not simulate the hardware completely, you executed the modified instruction. On real hardware running normally the real instruction would already be in the queue and the modified memory location wouldnt cause any damage so long as you didnt execute that string of instructions again. You could probably still use a trick like this today as pipelined processors fetch the next instruction. Or if you know that the hardware has a separate instruction and data cache you can modify a number of bytes ahead if you align this code in the cache line properly, the modified byte will not be written through the instruction cache but the data cache, and an instruction set simulator that did not have proper cache simulators would fail to execute properly. I think software only solutions are not going to get you very far.
上面这些都是老的和众所周知的,我对当前的工具了解不够,不知道它们是否已经围绕这些事情工作了。自修改代码可能/将使调试器出错,但是人类可以/将缩小问题范围,然后看到自修改代码并解决它。
It used to be that the hackers would take about 18 months to work something out, dvds for example. Now they are averaging around 2 days to 2 weeks (if motivated) (blue ray, iphones, etc). That means to me if I spend more than a few days on security, I am likely wasting my time. The only real security you will get is through hardware (for example your instructions are encrypted and only the processor core well inside the chip decrypts just before execution, in a way that it cannot expose the decrypted instructions). That might buy you months instead of days.
另外,读读凯文·米特尼克的《欺骗的艺术》。这样的人可以拿起电话,让你或同事把秘密交给系统,以为那是公司其他部门的经理、其他同事或硬件工程师。你的安全系统也被破坏了。安全不仅仅是管理技术,还要管理人。
安布尔说的完全正确。你可以让逆向工程变得更难,但你永远无法阻止它。永远不要相信依赖于防止逆向工程的“安全性”。
That said, the best anti-reverse-engineering techniques that I've seen focused not on obfuscating the code, but instead on breaking the tools that people usually use to understand how code works. Finding creative ways to break disassemblers, debuggers, etc is both likely to be more effective and also more intellectually satisfying than just generating reams of horrible spaghetti code. This does nothing to block a determined attacker, but it does increase the likelihood that J Random Cracker will wander off and work on something easier instead.