How do I protect Python code?

How do I protect Python code?

I am developing a piece of software in Python that will be distributed to my employer's customers. My employer wants to limit the usage of the software with a time restricted license file.

If we distribute the .py files or even .pyc files it will be easy to (decompile and) remove the code that checks the license file.

Another aspect is that my employer does not want the code to be read by our customers, fearing that the code may be stolen or at least the "novel ideas".

Is there a good way to handle this problem? Preferably with an off-the-shelf solution.

The software will run on Linux systems (so I don't think py2exe will do the trick).

Answer by Ned Batchelder for How do I protect Python code?

Python, being a byte-code-compiled interpreted language, is very difficult to lock down. Even if you use a exe-packager like py2exe, the layout of the executable is well-known, and the Python byte-codes are well understood.

Usually in cases like this, you have to make a tradeoff. How important is it really to protect the code? Are there real secrets in there (such as a key for symmetric encryption of bank transfers), or are you just being paranoid? Choose the language that lets you develop the best product quickest, and be realistic about how valuable your novel ideas are.

If you decide you really need to enforce the license check securely, write it as a small C extension so that the license check code can be extra-hard (but not impossible!) to reverse engineer, and leave the bulk of your code in Python.

Answer by fwzgekg for How do I protect Python code?

You should take a look at how the guys at getdropbox.com do it for their client software, including Linux. It's quite tricky to crack and requires some quite creative disassembly to get past the protection mechanisms.

Answer by Aaron Digulla for How do I protect Python code?

Is your employer aware that he can "steal" back any ideas that other people get from your code? I mean, if they can read your work, so can you theirs. Maybe looking at how you can benefit from the situation would yield a better return of your investment than fearing how much you could lose.

[EDIT] Answer to Nick's comment:

Nothing gained and nothing lost. The customer has what he wants (and paid for it since he did the change himself). Since he doesn't release the change, it's as if it didn't happen for everyone else.

Now if the customer sells the software, they have to change the copyright notice (which is illegal, so you can sue and will win -> simple case).

If they don't change the copyright notice, the 2nd level customers will notice that the software comes from you original and wonder what is going on. Chances are that they will contact you and so you will learn about the reselling of your work.

Again we have two cases: The original customer sold only a few copies. That means they didn't make much money anyway, so why bother. Or they sold in volume. That means better chances for you to learn about what they do and do something about it.

But in the end, most companies try to comply to the law (once their reputation is ruined, it's much harder to do business). So they will not steal your work but work with you to improve it. So if you include the source (with a license that protects you from simple reselling), chances are that they will simply push back changes they made since that will make sure the change is in the next version and they don't have to maintain it. That's win-win: You get changes and they can make the change themselves if they really, desperately need it even if you're unwilling to include it in the official release.

Answer by Peter M for How do I protect Python code?

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 by S.Lott for How do I protect Python code?

"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 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 do 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 by Oddthinking for How do I protect Python code?

In some circumstances, it may be possible to move (all, or at least a key part) of the software into a web service that your organization hosts.

That way, the license checks can be performed in the safety of your own server room.

Answer by dbr for How do I protect Python code?

Depending in who the client is, a simple protection mechanism, combined with a sensible license agreement will be far more effective than any complex licensing/encryption/obfuscation system.

The best solution would be selling the code as a service, say by hosting the service, or offering support - although that isn't always practical.

Shipping the code as .pyc files will prevent your protection being foiled by a few #s, but it's hardly effective anti-piracy protection (as if there is such a technology), and at the end of the day, it shouldn't achieve anything that a decent license agreement with the company will.

Concentrate on making your code as nice to use as possible - having happy customers will make your company far more money than preventing some theoretical piracy..

Answer by Peter Parker for How do I protect Python code?

What about signing your code with standard encryption schemes by hashing and signing important files and checking it with public key methods?

In this way you can issue license file with a public key for each customer.

Additional you can use an python obfuscator like this one (just googled it).

Answer by e-satis for How do I protect Python code?

Python is not the tool you need

You must use the right tool to do the right thing, and Python was not designed to be obfuscated. It's the contrary; everything is open or easy to reveal or modify in Python because that's the language's philosophy.

If you want something you can't see through, look for another tool. This is not a bad thing, it is important that several different tools exist for different usages.

Obfuscation is really hard

Even compiled programs can be reverse-engineered so don't think that you can fully protect any code. You can analyze obfuscated PHP, break the flash encryption key, etc. Newer versions of Windows are cracked every time.

Having a legal requirement is a good way to go

You cannot prevent somebody from misusing your code, but you can easily discover if someone does. Therefore, it's just a casual legal issue.

Code protection is overrated

Nowadays, business models tend to go for selling services instead of products. You cannot copy a service, pirate nor steal it. Maybe it's time to consider to go with the flow...

Answer by Brian C. Lane for How do I protect Python code?

The best you can do with Python is to obscure things.

• Strip out all docstrings
• Distribute only the .pyc compiled files.
• freeze it
• Obscure your constants inside a class/module so that help(config) doesn't show everything

You may be able to add some additional obscurity by encrypting part of it and decrypting it on the fly and passing it to eval(). But no matter what you do someone can break it.

None of this will stop a determined attacker from disassembling the bytecode or digging through your api with help, dir, etc.

Answer by Konrads for How do I protect Python code?

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 by Alex Coventry for How do I protect Python code?

The reliable only way to protect code is to run it on a server you control and provide your clients with a client which interfaces with that server.

Answer by I K for How do I protect Python code?

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.

Answer by bhadra for How do I protect Python code?

I understand that you want your customers to use the power of python but do not want expose the source code.

Here are my suggestions:

(a) Write the critical pieces of the code as C or C++ libraries and then use SIP or swig to expose the C/C++ APIs to Python namespace.

(b) Use cython instead of Python

(c) In both (a) and (b), it should be possible to distribute the libraries as licensed binary with a Python interface.

Answer by Erik Forsberg for How do I protect Python code?

Shipping .pyc files has its problems - they are not compatible with any other python version than the python version they were created with, which means you must know which python version is running on the systems the product will run on. That's a very limiting factor.

Answer by Piotr Czapla for How do I protect Python code?

Another attempt to make your code harder to steal is to use jython and then use java obfuscator.

This should work pretty well as jythonc translate python code to java and then java is compiled to bytecode. So ounce you obfuscate the classes it will be really hard to understand what is going on after decompilation, not to mention recovering the actual code.

The only problem with jython is that you can't use python modules written in c.

Answer by Mikael Lepistö for How do I protect Python code?

Idea of having time restricted license and check for it in locally installed program will not work. Even with perfect obfuscation, license check can be removed. However if you check license on remote system and run significant part of the program on your closed remote system, you will be able to protect your IP.

Preventing competitors from using the source code as their own or write their inspired version of the same code, one way to protect is to add signatures to your program logic (some secrets to be able to prove that code was stolen from you) and obfuscate the python source code so, it's hard to read and utilize.

Good obfuscation adds basically the same protection to your code, that compiling it to executable (and stripping binary) does. Figuring out how obfuscated complex code works might be even harder than actually writing your own implementation.

This will not help preventing hacking of your program. Even with obfuscation code license stuff will be cracked and program may be modified to have slightly different behaviour (in the same way that compiling code to binary does not help protection of native programs).

In addition to symbol obfuscation might be good idea to unrefactor the code, which makes everything even more confusing if e.g. call graphs points to many different places even if actually those different places does eventually the same thing.

Logical signature inside obfuscated code (e.g. you may create table of values which are used by program logic, but also used as signature), which can be used to determine that code is originated from you. If someone decides to use your obfuscated code module as part of their own product (even after reobfuscating it to make it seem different) you can show, that code is stolen with your secret signature.

Answer by Macke for How do I protect Python code?

Compile python and distribute binaries!

Sensible idea:

Use Cython (or something similar) to compile python to C code, then distribute your app as python binary libraries (pyd) instead.

That way, no Python (byte) code is left and you've done any reasonable amount of obscurification anyone (i.e. your employer) could expect from regular Code, I think. (.NET or Java less safe than this case, as that bytecode is not obfuscated and can relatively easily be decompiled into reasonable source.)

Cython is getting more and more compatible with CPython, so I think it should work. (I'm actually considering this for our product.. We're already building some thirdparty libs as pyd/dlls, so shipping our own python code as binaries is not a overly big step for us.)

See This Blog Post (not by me) for a tutorial on how to do it. (thx @hithwen)

Crazy idea:

You could probably get Cython to store the C-files separately for each module, then just concatenate them all and build them with heavy inlining. That way, your Python module is pretty monolithic and difficult to chip at with common tools.

Beyond crazy:

You might be able to build a single executable if you can link to (and optimize with) the python runtime and all libraries (dlls) statically. That way, it'd sure be difficult to intercept calls to/from python and whatever framework libraries you use. This cannot be done if you're using LGPL code though.

Answer by Ali AlNoaimi for How do I protect Python code?

using cxfreeze ( py2exe for linux ) will do the job.

http://cx-freeze.sourceforge.net/

it is available in ubuntu repositories

Answer by Ben Reynwar for How do I protect Python code?

www.bitboost.com offers a python obfuscator. Full disclosure: the author is a friend of mine.