Take the 2-minute tour ×
Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. It's 100% free, no registration required.

I have a web-software project which needs a bit of protection in form of authencitation…

This web based software runs on an intranet. There is no access to the internet from these terminal machines. Nevertheless, I want to stop anybody who copies the (PHP-based) software and tries to run that software on another machine. Simpler said: it should only run in the machine in which it got installed and just stop during authentication-level on any other machine.

I would be grateful to anybody who can suggest me the logic of achieving it.

share|improve this question
Can not be done securely, sorry. You simply can not prevent a person from copying something if he has access to it. –  nightcracker Nov 21 '13 at 9:22
An attacker can always rewrite the client and remove the the check. –  CodesInChaos Nov 21 '13 at 9:24
This isn't about crypto. At best it's about security, but even there it's security-through-obscurity. –  CodesInChaos Nov 21 '13 at 9:26
"Trying to make digital files uncopyable is like trying to make water not wet" Bruce Schneier ! –  sashank Nov 21 '13 at 10:22
@sashank Nice quote, but… OP is not asking how to prevent a file copy; OP wants to know how to prevent script execution on non-authorized machines. ;) –  e-sushi Nov 21 '13 at 10:44
show 4 more comments

closed as off-topic by CodesInChaos, nightcracker, figlesquidge, Gilles, archie Nov 21 '13 at 19:33

  • This question does not appear to be about cryptography within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

1 Answer

Thinking "crypto"…

One way I could imagine how you achieving at least some kind of copy-protection on your PHP-based scripts is to use solutions like these random search results: sourcecop, sourceguardian, phpcipher, … or the more well-known, and well-vetted Zend Guard or IonCube PHP Encoder who prevent reverse engineering through PHP encoding and obfuscation and thereby protecting your PHP code from unauthorized use.

But while those (partly cryptographic) script-protection solutions protect your PHP sourcecode, they (mostly) will not lock the scripts down to a single machine…

Blending in additional "security"…

To make the "encrypted PHP scripts" idea usable in your case, you could make your encrypted scripts dependent on some kind of self-coded PHP extension/module that locks itself to a single machine by letting the module verify a machine fingerprint (which includes several serial numbers, hardware configuration, etc.). Somewhat like cryptographically secure RNGs are seeded, but you would be looking for fixed and unique instead of variable and random hardware infos.

Thinking about it, you would probably be able to solve your problem by starting out with that PHP module and make it (a) machine-dependent, and (b) handle the cryptography of your encrypted scripts. If the module isn't in place and verified it's running on the correct machine, the scripts would not execute either as they would look to the PHP interpreter as if they were random digital garbage.

But the downsides of such an approach are pretty clear too, indicating that this is not an option for regular intranet projects. You would need to code (C/C++) a PHP module from scratch, you would need to get the crypto right, you would need to handle potential bottlenecks and slowdowns due to the PHP module's calculations, and much… much more.

And even then, someone who's able to reverse-engineer your module (or emulate the hardware environment parameters the module checks) would be able to "break" your protection. After all, if an attacker can grab your PHP files from your intranet server, he won't have too much of a problem grabbing your PHP module too. The rest of the attacker's job would boil down to a reverse-engineering effort.


Obviously, there are some potential options that could tackle the problem, but unless you are working on a big project for some government/corporation/institution, it'll be "overkill" to even think about practically implementing them as they will simply use up too much time and manpower to create from scratch.

From my point of view, the cheapest, the fastest, and the safest way to protect your PHP scripts would not be by means of modern cryptography, but by buying a good lock for your server-room. After all, restricting physical access is the safest way to stop an attacker from copying files from the (locked-in) intranet server. And if you're really fond of cryptography, get one of those electronic locks with a nice interface to put next to the server-room's door… it looks good and entertains you with lock-codes. ;) Throw Zend Guard or IonCube PHP Encoder on top of that and you should be able to say "mission accomplished" — but only for non-critical, civilian purposes where the sole goal is to protect your PHP scripts from being stolen and executed/run on another computer system.

share|improve this answer
Thanks a lot for your suggestion. I really appreciate the way you talked about that "overkill". Its a small stand alone application and there is no so called server. It just runs on the local server. However if anyboby copies the folder and then moves it to some other location; it can easily run on it.Is it possible to make some kind of key generation which makes the software to get only installed if that key is produced.And every key gets expired once it is installed. Since there is no server to trace the authentication of the keys. Is there any other way to achieve the same thing... –  Supra Nov 21 '13 at 17:06
@Supra Like I said in a comment: "I have to say that I was a bit shocked to discover that there are no real "cryptographically secure" (as in: "proven to be secure") solutions available that cover such a scenario. I guess buying padlocks is still cheaper than developing crypto-modules and handling certificates. ;)" — Which practically translates to a simpler answer to your question: "No, in the case you describe there is no solution available." –  e-sushi Nov 21 '13 at 17:53
add comment

Not the answer you're looking for? Browse other questions tagged or ask your own question.