RSA-based digital signature

For this homework I need to implement a HTTP public-key repository for key exchange that employs RSA-Based digital signatures, so for make this assignment I used PHP and a little database in mysql also a little script in Python.

First of all, this is my code:

This is the PHP+MySQL code

This is the Python script.

This is the MySQL database.
You can access to the application robertomtz.comeze.com/cripto.php

This is useful for example, I am not sure that cecy is the same person that I am chatting on facebook, so Cecy is on my database with a public key and I sent a challenge to Cecy and she download a script that run in local, put her keys and compute a r, she sent me the r and I verify in my web that it was Cecy.

This is an example that I made with Cecy 

If I put an incorrect Response:

:)