Protect Python Scripts By Pyarmor

Pyarmor is a command line tool used to import or run obfuscated Python scripts. It protects Python scripts by the following ways:

• Obfuscate source file to protect constants and literal strings.
• Obfuscate byte code of each code object.
• Clear f_locals of frame as soon as code object completed execution.
• Expired obfuscated scripts, or bind to fixed machine.

Look at what happened after foo.py is obfuscated by Pyarmor. Here it's file list in the output path dist

    foo.py

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

    pyshield.key
    pyshield.lic
    product.key
    license.lic

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

    from pytransfrom 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 foo.py can be used as normal Python script.

There are 2 phases for Pyarmor to protect Python scrpts:

• Build obfuscated script
• Run or import obfuscated script

Build Obfuscated Script

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 the code object as the following way:

• Wrap byte code co_code, insert a try...finally block

    wrap header:

            LOAD_GLOBALS    N (__armor_enter__)
            CALL_FUNCTION   0
            POP_TOP
            SETUP_FINALLY   F (jump to wrap footer, the code of finally block)

    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 flag in co_flags

• Change all code object 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

In order to run the obfuscated script, there are 3 functions need to be added to builtins module:

• __pyarmor__
• __armor_enter__
• __armor_exit__

It can be done by the following lines, which called Bootstrap Code

    from pytransfrom import pyarmor_runtime
    pyarmor_runtime()

When obufscated module is imported by Python interpreter:

• __pyarmor__ is called at first, it will import obufscated module

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

• __armor_enter__ is called as soon as code object is executed

    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
        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

    static PyObject *
    exit_armor(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
        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;
    }

Expired Obfuscated Script

By default the obfuscated scripts can run in any machine and never expired. This behaviour can be changed by replacing runtime file dist/license.lic

First generate an expired license:

    python pyarmor.py licenses --expired 2018-12-31 Customer-Jondy

It will make a new license.lic, replace dist/license.lic with this one. The obfuscated script will not work after 2018.

Now generate a license bind to fixed machine:

    python pyarmor.py licenses --bind-hard "100304PBN2081SF3NJ5T"
                               --bind-mac "70:f1:a1:23:f0:94"
                               --bind-ipv4 "202.10.2.52"
                               Customer-Jondy

Interesting? More information visit https://github.com/dashingsoft/pyarmor