Secure back door 0.5

Secure Back Door (SBD) is a tool that provides ultra-secure and minimal access to a computer, which allows you to run a single command based on a one time key. It is good if you dont want to have an SSH server running all the time, and only want to start it when needed. Because it has only a few lines of code, it is hoped that it will be less susceptible to security exploits than a program like SSH.
The protocol is detailed to an extent in the text file PROTOCOL, I will update it with more details as I have time, but the most important details are included already.
If you are a crypt analysis, or just like a challenge, I appreciate anyone who is willing to look through the protocol and/or code and point out possible security implications and flaws in design!
Enhancements:
- Fixed a few minor compiler warnings
- Updated license year to 2005
- Uncommented execution code in sbdd, so now sbdd will execute incoming commands
- Updated README documentation for compilation