Encrypt resources in Cocoa app?

Question

Hi,

I have a shell script stored in the resources folder of my Cocoa app. If used improperly it could be dangerous (even though I have taken precautions to reduce exploits, such as using the absolute path to commands) so is there any way to encrypt the script in binary format, then decrypt it when it needs to be used?

Thanks

Answer 1

No. If the user will decrypt it to use it, then she can see (and intercept) the clear text at some point. If you think you have "shell-like" things to do, do them in C/ObjC... This can be your friend.

Answer 2

What you're asking for is essentially DRM. A different purpose (“security” instead of thwarting copyright infringement), but the same approach, with the same problems.

In order for the user to be able to normally use the (music|video|script), they must be able to decrypt it. You would do this for them under only the right conditions in your (player|app), but that doesn't matter: no matter how well you hide it, you still have to provide the user with all the technology and keys necessary to decrypt the (music|video|script), so that your (player|app) can do that.

And then, since the user has all the technology and keys necessary to decrypt it, an attacker can and eventually will uncover them all and decrypt the (music|video|script) on their own.

I second Massa's suggestion of switching away from a shell script. This doesn't completely eliminate risk: If an attacker can gain access to write to your shell script, they can gain access to write to a Mach-O executable just as easily. But editing a Mach-O executable is not nearly as easy, so you are at least raising the bar that way.

Answer 3

It seems as if your concern is about people getting write access to the script and modifying it to run arbitrary code. You could keep a checksum for the script in the binary and compare that with the checksum of the script before you run it. Now, how do you stop people from editing the binary too? Code signing. In fact, if you keep the shell script in the app bundle then editing the script will break the signature of the bundle anyway.

Answer 4

This does not make a lot of sense. If an attacker has access to edit this script file, then they likely have access to edit any number of files, your application is less likely to be a security risk than any number of other things would be attacker could do.