[HH] D-I-Y hardware random number generator USB dongle

[Tom Metro]

A thumb-drive size dongle using a USB serial converter, an ATTiny45
micro, and the entropy-lib library, which uses the micro's "watchdog
timer's natural jitter to produce a reliable stream of true random
numbers. Unlike other methods currently available, this library requires
no external hardware and produces a considerably more random number
stream than methods based upon the technique of reading an unconnected
analog pin."

http://forums.hackaday.com/viewtopic.php?f=3&t=4189

The author notes, "The TRNG dongle is quite slow when it comes to
generation of random numbers. The Entropy.random() call waits for some
time till enough entropy is gathered. It will produce around two 32bit
random numbers a second. It is not much but it is enough for my needs.
If you are looking for a quite inexpensive but much more performant
solution, check the NeuG dongle based on a STM32
http://www.seeedstudio.com/wiki/FST-01"

 -Tom