1. DIY: A 10-year old child should be able to do it
2. High quality: true 256bit randomness
3. Human verifiable: using CCD noise or radioactive decay is not acceptable because it is difficult to verify the randomness
4. Low cost: cheap, not too time-consuming to generate a random number
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Procedures:
1. Buy a deck of at least 43 blank, name card sized, white paper cards. All cards should be perfectly same size
2. Pick a card, write "1" and "2" on it in this way:
3. Flip to the other side, write "3" and "4" in the same way
4. Pick another card, write "5", "6", "7", "8" in the same way
5. Repeat for totally 43 cards (1 to 172)
6. Put the cards into a big black bag
7. Shake the bag really really vigorously and randomly
8. Stake the cards without looking a them
9. Determine the "upper side" of the deck without looking at it. (To determine the upper side, there are 2 dimensions)
10. By the order of the cards, write down the numbers on the upper side
11. You have a sequence of 43 numbers with 261bit entropy. Do whatever you want with it
Permutation of 43 cards give you 175 bits, and the orientation of each card gives you 2 extra bits
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If you are able to find some perfectly square cards, you can reduce the number of cards to 38 by doing like this:
So each card will have 8 numbers on it.
Permutation of 38 cards give you 148 bits, and the orientation of each card gives you 3 extra bits. Totally you get 262 bits.
You can also do the same with 34 perfect octagon cards.
Having smaller number of cards will not only save you some time, but also make the shuffling easier and thus more random
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Why not standard playing cards? A full deck of 54 cards give only 237 bits, and more cards means more time to record the results
Other ideas are welcomed