Crypto Challenges

This PL includes the new crypto challenges that were created as a part of GSoC Program.
The challenges include:
<ul>
  <li> Classical Ciphers </li>
  <li> Multiple OTP </li>
  <li> Cascade MACs</li>
  <li> RSA </li>
  <li> Blinding Signatures </li>
</ul>
Among others.