Some time ago, in my work I needed to protect some classes against other people to read the code. For that purpose, I created a EncryptedClassLoader, that loaded previously encrypted classes, and can load normal (not encrypted) classes as well. Working in that way was a little complicated, and testing too (compile, then encrypt, and then decrypt).
Is there any free framework to do what I needed, and is easy to handle? I mean, not only obfuscate, but also encrypt the files, so none can read or debug that part of code. It would also be great that I can change the keys for encryption easily (in my application, it was hardcoded).
Thanks in advance.
Short answer, you can't. Encryption doesn't work. Here's an oldish article about why it's pointless to use an encrypted class loader:
Unfortunately, you would be wrong, both in thinking that you were the first to come up with this idea and in thinking that it actually works. And the reason has nothing to do with the strength of your encryption scheme.
You can obfuscate it, but that will only go so far, and in the end I'm a firm believer that your time would be better spend fixing bugs or adding features.