lucius

Regards everybody, I'm distributing an application that needs a licence file protection. A file comes with a registered version that contains encrypted customer data. It's encrypted using asynchronous encryption (RSA). The idea is to encrypt the file with a private key, and give the public key to the application. So the application could decrypt the file, but would not be able to encrypt it. The goal is to make it as difficult as possible to make a keygen that would work on unmodified application assembly (with the original, unpatched exe that contains the unmodified public key). I planned to do this by separating public and private keys, and giving only the public key part to the application. 1. I don't know if it is possible to decrypt using only the public key, so that's my first question. Can I switch public and private keys this way ? Can the user decrypt using only the public key ? 2. Second question (given the premise that we're not modifiying the assembly or memory during runtime): Is this idea good ? Would it be secure ?