Hi bl4d3,
Here is all the information about the one wire protocol for the DS18B20 including a sketch and libraries. I have no idea when it comes to programming in C so can't help any further with that but everything you need should be on that page.
There are a couple of different models of these sensors but the above one is the newest one and they are pretty much the same anyway, this is all detailed at that link.
http://www.arduino.cc/playground/Learning/OneWire
With the security side of things. Personally, I think the risk is low and both those suggestions used together would work fine.
Another thought, with your remote server stuff, have you considered including the ability to send a feed to pachube to monitor and graph reading from the sensors?
Keep up the good work mate. Don't work too hard though, I think if you get a good, stable base product working and build on it from there this could become very popular!
Cheers,
BT