How do I protect Python code? [closed]

Answer 1

Do not rely on obfuscation. As You have correctly concluded, it offers very limited protection. UPDATE: Here is a link to paper which reverse engineered obfuscated python code in Dropbox. The approach - opcode remapping is a good barrier, but clearly it can be defeated.

Instead, as many posters have mentioned make it:

• Not worth reverse engineering time (Your software is so good, it makes sense to pay)
• Make them sign a contract and do a license audit if feasible.

Alternatively, as the kick-ass Python IDE WingIDE does: Give away the code. That's right, give the code away and have people come back for upgrades and support.

Answer 2

I have looked at software protection in general for my own projects and the general philosophy is that complete protection is impossible. The only thing that you can hope to achieve is to add protection to a level that would cost your customer more to bypass than it would to purchase another license.

With that said I was just checking google for python obsfucation and not turning up a lot of anything. In a .Net solution, obsfucation would be a first approach to your problem on a windows platform, but I am not sure if anyone has solutions on Linux that work with Mono.

The next thing would be to write your code in a compiled language, or if you really want to go all the way, then in assembler. A stripped out executable would be a lot harder to decompile than an interpreted language.

It all comes down to tradeoffs. On one end you have ease of software development in python, in which it is also very hard to hide secrets. On the other end you have software written in assembler which is much harder to write, but is much easier to hide secrets.

Your boss has to choose a point somewhere along that continuum that supports his requirements. And then he has to give you the tools and time so you can build what he wants. However my bet is that he will object to real development costs versus potential monetary losses.

Answer 3

Use the same way to protect binary file of c/c++, that is, obfuscate each function body in executable or library binary file, insert an instruction "jump" at the begin of each function entry, jump to special function to restore obfuscated code. Byte-code is binary code of Python script, so

• First compile python script to code object
• Then iterate each code object, obfuscate co_code of each code object as the following

    0   JUMP_ABSOLUTE            n = 3 + len(bytecode)

    3
    ...
    ... Here it's obfuscated bytecode
    ...

    n   LOAD_GLOBAL              ? (__pyarmor__)
    n+3 CALL_FUNCTION            0
    n+6 POP_TOP
    n+7 JUMP_ABSOLUTE            0

• Save obfuscated code object as .pyc or .pyo file

Those obfuscated file (.pyc or .pyo) can be used by normal python interpreter, when those code object is called first time

• First op is JUMP_ABSOLUTE, it will jump to offset n

• At offset n, the instruction is to call a PyCFunction. This function will restore those obfuscated bytecode between offset 3 and n, and put the original byte-code at offset 0. The obfuscated code can be got by the following code

      char *obfucated_bytecode;
      Py_ssize_t len;
      PyFrameObject* frame = PyEval_GetFrame();
      PyCodeObject *f_code = frame->f_code;
      PyObject *co_code = f_code->co_code;      
      PyBytes_AsStringAndSize(co_code, &obfucated_bytecode, &len)
  

• After this function returns, the last instruction is to jump to offset 0. The really byte-code now is executed.

There is a tool Pyarmor to obfuscate python scripts by this way.

Answer 4

"Is there a good way to handle this problem?" No. Nothing can be protected against reverse engineering. Even the firmware on DVD machines has been reverse engineered and the AACS Encryption key exposed. And that's in spite of the DMCA making that a criminal offense.

Since no technical method can stop your customers from reading your code, you have to apply ordinary commercial methods.

1. Licenses. Contracts. Terms and Conditions. This still works even when people can read the code. Note that some of your Python-based components may require that you pay fees before you sell software using those components. Also, some open-source licenses prohibit you from concealing the source or origins of that component.

2. Offer significant value. If your stuff is so good -- at a price that is hard to refuse -- there's no incentive to waste time and money reverse engineering anything. Reverse engineering is expensive. Make your product slightly less expensive.

3. Offer upgrades and enhancements that make any reverse engineering a bad idea. When the next release breaks their reverse engineering, there's no point. This can be carried to absurd extremes, but you should offer new features that make the next release more valuable than reverse engineering.

4. Offer customization at rates so attractive that they'd rather pay you to build and support the enhancements.

5. Use a license key which expires. This is cruel, and will give you a bad reputation, but it certainly makes your software stop working.

6. Offer it as a web service. SaaS involves no downloads to customers.

Answer 5

I think there is one more method to protect your Python code; part of the Obfuscation method. I believe there was a game like Mount and Blade or something that changed and recompiled their own python interpreter (the original interpreter which i believe is open source) and just changed the OP codes in the OP code table to be different then the standard python OP codes.

So the python source is unmodified but the file extensions of the *.pyc files are different and the op codes don't match to the public python.exe interpreter. If you checked the games data files all the data was in Python source format.

All sorts of nasty tricks can be done to mess with immature hackers this way. Stopping a bunch of inexperienced hackers is easy. It's the professional hackers that you will not likely beat. But most companies don't keep pro hackers on staff long I imagine (likely because things get hacked). But immature hackers are all over the place (read as curious IT staff).

You could for example, in a modified interpreter, allow it to check for certain comments or doc strings in your source. You could have special OP codes for such lines of code. For example:

OP 234 is for source line "# Copyright I wrote this" or compile that line into op codes that are equivalent to "if False:" if "# Copyright" is missing. Basically disabling a whole block of code for what appears to be some obscure reason.

One use case where recompiling a modified interpreter may be feasible is where you didn't write the app, the app is big, but you are paid to protect it, such as when you're a dedicated server admin for a financial app.

I find it a little contradictory to leave the source or opcodes open for eyeballs, but use SSL for network traffic. SSL is not 100% safe either. But it's used to stop MOST eyes from reading it. A wee bit precaution is sensible.

Also, if enough people deem that Python source and opcodes are too visible, it's likely someone will eventually develop at least a simple protection tool for it. So the more people asking "how to protect Python app" only promotes that development.

Answer 6

Though there's no perfect solution, the following can be done:

1. Move some critical piece of startup code into a native library.
2. Enforce the license check in the native library.

If the call to the native code were to be removed, the program wouldn't start anyway. If it's not removed then the license will be enforced.

Though this is not a cross-platform or a pure-Python solution, it will work.