Quote from: robanswe on October 26, 2013, 09:40:01 AM

Quote from: chrisrico on October 25, 2013, 10:05:24 PM

Can I ask why you want to use dice as a source of entropy?

It's easy and nothing should be able to go wrong. I mean a lot can go wrong while setting up some sort of space noise receiver.

Uh, actually it is surprisingly easy to fuck up dice rolling for entropy. Any attempt to extract entropy from gross physical processes that requires human work is prone to failure. Just ask everyone that tried it during World War II.

Ideally, you should build a machine that shakes the dice in a cup and tips the cup into a flat, level tray. At the very least, use a cup, try to tip the cup the same way each time, and for the love of god, don't look in the cup while shaking or tossing. The tray should have a line painted in it about 1.5 die radiuses away from the wall and you should ignore any rolls where any of the dice touch or cross that line. Also reject any rolls where the dice are touching. Since dice touching can be somewhat subjective, it is also a good idea to reject any rolls where the dice end up within some objective threshold of each other, 1.5 radiuses perhaps. Build a gauge block of the appropriate width and taller than the dice and try to slip it between the dice if they are even remotely close.*

Next, all of your dice need to be different and distinct colors, and all faces must be instantly distinguishable (that means you need dots or lines on both 6 and 9, not just one). You must always assemble the rolls into your number in the same way. Print a data collection sheet with boxes, and color code the boxes to match the dice so that you don't mess up the ordering.**

And finally, never, ever, ever reject throws for subjective reasons. You must be extremely vigilant about this. Your natural tendency will be to reject throws that don't look random enough, or just don't look right in some obscure way. You must fight these thoughts and write down the data collected, exactly as it comes up, regardless of your personal feelings.

You'll note that most of my advice is in the area of removing your own judgement from the system. Your brain is a shitty discriminator of entropy, and if you let it interfere with the process, you will get shitty entropy out. During World War II (and the cold war, for that matter), office staff on all sides of the war were trained to generate encryption codes and pads by using physical systems like dice. They usually failed (and their codes were cracked, and people died) because they would have unhelpful thoughts like "that's too many 7s to be really random. I'm going to change a few". And that was generally after being trained specifically not to do that, and that lives depended on the quality of their work. Odds are very good that you will do at least as poorly as they did.

* The common theme here is to reject any rolls where the dice might be leaning on the wall or on other dice, which is to say when they might not be completely flat, which is to say when human judgment might possibly come into deciding which face is up. Setting the margin wide and using objective measures reduces the temptation to occasionally fudge things.

** Again, remove human judgment. If the die only has 6 or 9 marked, you will occasionally write the wrong number down. If you don't have a defined order, you will write them down in the order that "looks" most random to you.