protect-python-scripts-by-pyarmor.md

Protect Python Scripts By PyArmor

PyArmor is a command line tool used to obfuscate python scripts, bind obfuscated scripts to fixed machine or expire obfuscated scripts. It protects Python scripts by the following ways:

• Obfuscate code object to protect constants and literal strings.
• Obfuscate co_code of each function (code object) in runtime.
• Clear f_locals of frame as soon as code object completed execution.
• Verify the license file of obfuscated scripts while running it.

Look at what happened after foo.py is obfuscated by PyArmor. Here are the files list in the output path dist

    foo.py

    pytransform.py
    _pytransform.so, or _pytransform.dll in Windows, _pytransform.dylib in MacOS
    pytransform.key
    license.lic

dist/foo.py is obfuscated script, the content is

    from pytransform import pyarmor_runtime
    pyarmor_runtime()

    __pyarmor__(__name__, __file__, b'\x06\x0f...')

All the other extra files called Runtime Files, which are required to run or import obfuscated scripts. So long as runtime files are in any Python path, obfuscated script dist/foo.py can be used as normal Python script. That is to say:

The original python scripts can be replaced with obfuscated scripts seamlessly.

Obfuscated Python Scripts

How to obfuscate python scripts by PyArmor?

First compile Python script to code object

    char *filename = "foo.py";
    char *source = read_file( filename );
    PyCodeObject *co = Py_CompileString( source, "<frozen foo>", Py_file_input );

Next change this code object as the following ways

• Wrap byte code co_code within a try...finally block

    wrap header:

            LOAD_GLOBALS    N (__armor_enter__)     N = length of co_consts
            CALL_FUNCTION   0
            POP_TOP
            SETUP_FINALLY   X (jump to wrap footer) X = size of original byte code

    changed original byte code:

            Increase oparg of each absolute jump instruction by the size of wrap header

            Obfuscate original byte code

            ...

    wrap footer:

            LOAD_GLOBALS    N + 1 (__armor_exit__)
            CALL_FUNCTION   0
            POP_TOP
            END_FINALLY

• Append function names __armor_enter, __armor_exit__ to co_consts

• Increase co_stacksize by 2

• Set CO_OBFUSCAED (0x80000000) flag in co_flags

• Change all code objects in the co_consts recursively

Then serialize this reformed code object, obfuscate it to protect constants and literal strings

    char *string_code = marshal.dumps( co );
    char *obfuscated_code = obfuscate_algorithm( string_code  );

Finally generate obfuscated script

    sprintf( buf, "__pyarmor__(__name__, __file__, b'%s')", obfuscated_code );
    save_file( "dist/foo.py", buf );

The obfuscated script is a normal Python script, it looks like this

    __pyarmor__(__name__, __file__, b'\x01\x0a...')

Run Obfuscated Script

How to run obfuscated script dist/foo.py by Python Interpreter?

The first 2 lines, which called Bootstrap Code

    from pytransform import pyarmor_runtime
    pyarmor_runtime()

It will fulfil the following tasks

• Load dynamic library _pytransform by ctypes
• Check dist/license.lic is valid or not
• Add 3 cfunctions to module builtins
  • __pyarmor__
  • __armor_enter__
  • __armor_exit__

The next code line in dist/foo.py is

    __pyarmor__(__name__, __file__, b'\x01\x0a...')

__pyarmor__ is called, it will import original module from obfuscated code

    static PyObject *
    __pyarmor__(char *name, char *pathname, unsigned char *obfuscated_code)
    {
        char *string_code = restore_obfuscated_code( obfuscated_code );
        PyCodeObject *co = marshal.loads( string_code );
        return PyImport_ExecCodeModuleEx( name, co, pathname );
    }

After that, in the runtime of this python interpreter

• __armor_enter__ is called as soon as code object is executed, it will restore byte-code of this code object

    static PyObject *
    __armor_enter__(PyObject *self, PyObject *args)
    {
        // Got code object
        PyFrameObject *frame = PyEval_GetFrame();
        PyCodeObject *f_code = frame->f_code;

        // Increase refcalls of this code object
        // Borrow co_names->ob_refcnt as call counter
        // Generally it will not increased  by Python Interpreter
        PyObject *refcalls = f_code->co_names;
        refcalls->ob_refcnt ++;

        // Restore byte code if it's obfuscated
        if (IS_OBFUSCATED(f_code->co_flags)) {
            restore_byte_code(f_code->co_code);
            clear_obfuscated_flag(f_code);
        }

        Py_RETURN_NONE;
    }

• __armor_exit__ is called so long as code object completed execution, it will obfuscate byte-code again

    static PyObject *
    __armor_exit__(PyObject *self, PyObject *args)
    {
        // Got code object
        PyFrameObject *frame = PyEval_GetFrame();
        PyCodeObject *f_code = frame->f_code;

        // Decrease refcalls of this code object
        PyObject *refcalls = f_code->co_names;
        refcalls->ob_refcnt --;

        // Obfuscate byte code only if this code object isn't used by any function
        // In multi-threads or recursive call, one code object may be referenced
        // by many functions at the same time
        if (refcalls->ob_refcnt == 1) {
            obfuscate_byte_code(f_code->co_code);
            set_obfuscated_flag(f_code);
        }

        // Clear f_locals in this frame
        clear_frame_locals(frame);

        Py_RETURN_NONE;
    }

License of Obfuscated Scripts

When call pyarmor_runtime() in dist/foo.py, it will check the file dist/license.lic. If it's invalid, the python interpreter reports error and quits. The default license is generated while obfuscating Python scripts. It allows to run obfuscated scripts in any machine and never expired.

If we generate a new license which includes an expired date, or some hardware infromation, for examples, serial number of harddisk, mac address of network address etc. The obfuscated scripts will be aborted, if any of these conditions isn't satisfied in the target machine.

PyArmor has command hdinfo to print hardware information in target machine

    pyarmor hdinfo

PyArmor has command licenses used to generate new liceses

    pyarmor licenses
            --expired 2018-12-31
            --bind-disk "100304PBN2081SF3NJ5T"
            --bind-mac "70:f1:a1:23:f0:94"
            --bind-ipv4 "202.10.2.52"
            Customer-Jondy

More information visit PyArmor Homepage