Are dices for generating seed words fair? - page 4.

Medusah

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Quote from: LoyceV on October 27, 2023, 10:45:51 AM

Really? When I hit my keyboard 3 times with my non-mouse-hand, I get this: safdsafdsafd. I can easily reproduce it: safdsafdsafd. Again? safdsafdsafd.

It was just an example. If you mess with your keyboard, I expect to see "j" appearing more frequently than "+", because it is in the center of the keyboard.

Let me try. Deep breath...

Code:

jolzxcioadsfjopas9-f0-AS0-ASJ9J90-ASIASF890HASFh90-

See?

Anyway, just an example!

LoyceV

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Quote from: Medusah on October 27, 2023, 10:02:10 AM

You do not randomly press keys which would have bias on pressing "j" more often than "+" (example).

Really? When I hit my keyboard 3 times with my non-mouse-hand, I get this: safdsafdsafd. I can easily reproduce it: safdsafdsafd. Again? safdsafdsafd.

Medusah

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Not your coins, not your business

Quote from: philipma1957 on October 24, 2023, 03:54:37 PM

This finally hit me why it is wrong. The flipping must be done blindfolded and gloved to avoid a biased flipper that does not like your method.

How can the person have bias? The whole point of tossing coins is that the outcome is completely unpredictable for the person. You do not randomly press keys which would have bias on pressing "j" more often than "+" (example). Just take a coin and flip it using the same initial conditions (e.g. thumb nail touches tails).

LoyceV

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Quote from: larry_vw_1955 on October 26, 2023, 06:38:52 PM

you would need a device that can measure the temperature of each side of the coin simultaneously.

There won't be any temperature difference between sides, metals are excellent heat conductors.

larry_vw_1955

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Quote from: pinggoki on October 25, 2023, 02:24:07 AM

But if those factors don't affect the flip, wouldn't that mean your second statement should be ignored because it says to keep the conditions identical and those conditions are the factors that I have talked about right? But I guess you're right, it's not like those factors can quickly change unless there's a physical intervention.

for example, lets say the surface you are doing the flips on has a high temperature. then whatever side the coin lands on will get heated up more than the side that lands face up. you will need to take that into account. maybe wait in between flips until both sides equalize to room temperature. for that, you would need a device that can measure the temperature of each side of the coin simultaneously.

pinggoki

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Quote from: larry_vw_1955 on October 24, 2023, 08:45:05 PM

Quote from: pinggoki on October 24, 2023, 04:12:18 PM

~

they don't have any affect at all on the randomness apparently. as long as one does the von neuman method it doesn't matter about all of those external factors. Undecided

just make sure to keep the conditions identical throughout the entire coin flipping process and don't let any of those factors vary. should be a piece of cake.

But if those factors don't affect the flip, wouldn't that mean your second statement should be ignored because it says to keep the conditions identical and those conditions are the factors that I have talked about right? But I guess you're right, it's not like those factors can quickly change unless there's a physical intervention.

larry_vw_1955

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Quote from: pinggoki on October 24, 2023, 04:12:18 PM

Wouldn't the coin itself a factor to this too? Especially if you're not using the same coin to do the same flip on the machine and another factor is the atmosphere of the surrounding area and the hardness of the surface where the coin is going to land, the air resistance is always neglected in theory but in practical application, that's always considered right? And regarding the hardness of the surface, there's also the small grooves if the surface isn't smooth. Am I pedantic over this stuff or those can be considered a factor to the fairness of the flip?

they don't have any affect at all on the randomness apparently. as long as one does the von neuman method it doesn't matter about all of those external factors. Undecided

just make sure to keep the conditions identical throughout the entire coin flipping process and don't let any of those factors vary. should be a piece of cake.

pinggoki

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Quote from: LoyceV on October 20, 2023, 04:52:02 AM

My gut feeling tells me this spring would create the same result every time, because the initial conditions are the same. Unless the spring tension varies, in that case the spring tension becomes your random and you need to make sure there's no bias in it. Or the way you load the coin into the machine.
Just for fun: here's a Machine Flips a Coin 10,000 Times.

Wouldn't the coin itself a factor to this too? Especially if you're not using the same coin to do the same flip on the machine and another factor is the atmosphere of the surrounding area and the hardness of the surface where the coin is going to land, the air resistance is always neglected in theory but in practical application, that's always considered right? And regarding the hardness of the surface, there's also the small grooves if the surface isn't smooth. Am I pedantic over this stuff or those can be considered a factor to the fairness of the flip?

We did that kind of experiment back in my freshmen year in college although it's a programming test where we set the times a coin is flipped and then the computer returns the results of the set times that the coin was flipped.

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Quote from: o_e_l_e_o on October 19, 2023, 05:54:59 AM

Quote from: larry_vw_1955 on October 18, 2023, 11:29:16 PM

so under the assumption that HT and TH have equal probability that method seems good for eliminating bias but there is that assumption.

That's not an assumption - it's pure math.

Let's say your coin is biased to 60% heads, 40% tails. The probability of HT is 0.6*0.4 = 0.24. The probability of TH is 0.4*0.6 = 0.24. The probability is identical. This is the whole premise behind von Neumann's algorithm - you know HT and TH are equally probable without the need to perform any statistical testing of your coin.

This finally hit me why it is wrong. The flipping must be done blindfolded and gloved to avoid a biased flipper that does not like your method.

Your assumption is that the coin is biased not the flipper. If it is the flipper your method is not good. Ie the flipper may subconsciously be able to take a neutral perfect coin and make it do heads 60-40

or tails 40-60 on any toss. So he would ruin the neumann method. unless he flips it gloved and blindfolded.

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Quote from: NotATether on October 19, 2023, 07:33:32 AM

It makes me think: What would a device with a spring to launch the coin do? It would almost certainly eliminate all bias in coin tosses - provided it is engineered properly - and it could even be made into a wearable on your hand that you can use to emulate a traditional coin toss.

My gut feeling tells me this spring would create the same result every time, because the initial conditions are the same. Unless the spring tension varies, in that case the spring tension becomes your random and you need to make sure there's no bias in it. Or the way you load the coin into the machine.
Just for fun: here's a Machine Flips a Coin 10,000 Times.

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Quote from: larry_vw_1955 on October 19, 2023, 09:53:45 PM

you're assuming that the outcome of one coin toss does not have any affect on the outcome of the one after it.

As far as the coin goes, it makes no difference. The coin doesn't remember the previous result, and so previous tosses have no bearing on future tosses.

As far as you go, then the solution is as above. If you don't learn the outcome of the first toss, then it cannot bias any subsequent tosses.

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Quote from: o_e_l_e_o on October 19, 2023, 05:54:59 AM

That's not an assumption - it's pure math.

you're assuming that the outcome of one coin toss does not have any affect on the outcome of the one after it. you model that as though they are "independent" events but that needs to be tested to make sure that is actually the case, don't you think? otherwise how do you know?

Quote

Let's say your coin is biased to 60% heads, 40% tails. The probability of HT is 0.6*0.4 = 0.24. The probability of TH is 0.4*0.6 = 0.24. The probability is identical. This is the whole premise behind von Neumann's algorithm - you know HT and TH are equally probable without the need to perform any statistical testing of your coin.

forget about the formulas. talk about the real world tests that justify why they are independent. what tests have you done? Cheesy

did you flip a coin 10,000 times and count how many HT and TH you got? if not then there could be some systematic bias in the situation that you just arent aware of.

now i'm not saying that this method is inferior to just flipping a biased coin, surely its better than just that.

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Quote from: LoyceV on October 15, 2023, 05:36:51 AM

By coincidence, I stumbled upon an article about bias in coin tosses. It reminded me about this topic, hence the 10 month bump.

TL;DR: if you start a coin toll with heads up, there's a 50.8% chance you'll end up with heads.

This is the important part:

Quote from: Coin Tosses Are Not 50/50: Scientists Toss 350,757 Coins And Prove Old Theory

Delving into the data further, they found that coin tosses are highly variable between people, with some showing a strong same-side bias and others having none at all – coin tosses may come down (ever so slightly) to the tosser.

Some people have the bias and others don't.

It makes me think: What would a device with a spring to launch the coin do? It would almost certainly eliminate all bias in coin tosses - provided it is engineered properly - and it could even be made into a wearable on your hand that you can use to emulate a traditional coin toss.

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Quote from: larry_vw_1955 on October 18, 2023, 11:29:16 PM

so under the assumption that HT and TH have equal probability that method seems good for eliminating bias but there is that assumption.

That's not an assumption - it's pure math.

Let's say your coin is biased to 60% heads, 40% tails. The probability of HT is 0.6*0.4 = 0.24. The probability of TH is 0.4*0.6 = 0.24. The probability is identical. This is the whole premise behind von Neumann's algorithm - you know HT and TH are equally probable without the need to perform any statistical testing of your coin.

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Quote from: o_e_l_e_o on October 18, 2023, 06:06:17 AM

I don't think many people have the ability to alter their coin flipping technique to make one side or the other more likely. But even so, if you wanted to protect against this then don't learn the results, and that way the results cannot bias your flipping technique.

that's correct. that's only way to make sure.

Quote

Two options for this. If you have someone you trust completely with your bitcoin (such as a spouse), then have them note the results from the flips for you, while you don't even look.

the only way i would accept that solution is if you hand over your completed private key and wallet details to your spouse once done.

Quote

If you don't have someone you trust completely, then film the process using an airgapped device and watch the video back after you have made several hundred flips (on average with an unbiased coin you will need to make 512 flips to generate 128 bits of entropy).

correct. that's what i thought you might say. thats what i would have said.

so under the assumption that HT and TH have equal probability that method seems good for eliminating bias but there is that assumption. i guess most people accept it as a fact. which seems not unreasonable to want to do i guess. Shocked

to test that assumption one could take their particular coin and toss it a million times and see how often HT and TH showed up. should be about 500k times each. not sure where the cutoff would be to determine the assumption was problematic. maybe around 480k vs 520 ?

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Quote from: Medusah on October 18, 2023, 03:02:21 PM

For anyone who does not know: the von Neumann method involves counting results only half of the time ('HH', 'TT' are not counted). So for every two coin tosses which are 'HT' or 'TH' you add 1 bit. So 1 bit for every 4 coin tosses on average.

You can actually make it more efficient, but I've never bothered to talk about how you would do this on the forum since it is far easier and safer to just stick to the basic method and keep flipping until you have enough entropy. The more efficient method involves considering more than just pairs of flips. We know that HT and TH are equally probable, so by the same logic HH TT and TT HH are also equally probable. And these runs of matching pairs do not need to be consecutive. HH HT TT and TT HT HH are also equally probable, for example.

So you flip your coin, and for every HT you write down 0, and for every TH you write down 1. But then you also generate a completely separate second level sequence. For every HH you write down H in this second level sequence, and for every TT you write down T. You then run von Neumann's algorithm across this new sequence as well, generating 0s and 1s as before, but also generating Hs and Ts as described in a new third level sequence.

You can iterate this as many times as you like, and theoretically approach the maximum possible entropy you can extract from each flip. In practice, additional efficiency gains after probably the third level or so are probably outweighed by the increased complexity.

Medusah

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Not your coins, not your business

Quote from: o_e_l_e_o on October 18, 2023, 06:06:17 AM

(on average with an unbiased coin you will need to make 512 flips to generate 128 bits of entropy).

For anyone who does not know: the von Neumann method involves counting results only half of the time ('HH', 'TT' are not counted). So for every two coin tosses which are 'HT' or 'TH' you add 1 bit. So 1 bit for every 4 coin tosses on average.

I have not tried it. Sounds the most secure, but tiring too. Tongue

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Quote from: larry_vw_1955 on October 17, 2023, 10:32:27 PM

so i don't think it can get rid of that type of bias.

I don't think many people have the ability to alter their coin flipping technique to make one side or the other more likely. But even so, if you wanted to protect against this then don't learn the results, and that way the results cannot bias your flipping technique.

Two options for this. If you have someone you trust completely with your bitcoin (such as a spouse), then have them note the results from the flips for you, while you don't even look. If you don't have someone you trust completely, then film the process using an airgapped device and watch the video back after you have made several hundred flips (on average with an unbiased coin you will need to make 512 flips to generate 128 bits of entropy).

larry_vw_1955

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Quote from: o_e_l_e_o on October 16, 2023, 11:10:23 AM

Given that, and given that each coin itself will also have its own intrinsic bias, then again the solution is the simple one I've outlined many times before - use a von Neumann debiasing approach, but with the additional caveat that you should start each flip from the same position (i.e. heads face up). That way any bias in either the coin or your technique is completely eliminated and you will always end up with a completely random result.

the thing about that von neumann method is if the person rolling the dice knows they are using it then they also know that only the first flip matters. the 2nd flip never affects anything. except whether to use the result of the first flip or not. with all of that information in their head, they're not going to be flipping the first and second flips the same way. probably not.

example lets say you had this series of flips:

HH HT HT HT and then say your next flip was H you would be thinking "I don't want this to be T because we shouldn't be having too many H in a row"...so subconsciously your mind would be making you flip the coin so that the coin landed on H.

so i don't think it can get rid of that type of bias.

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Quote from: LoyceV on October 15, 2023, 05:36:51 AM

TL;DR: if you start a coin toll with heads up, there's a 50.8% chance you'll end up with heads.

I think far more interesting than that headline figure is the data they have given in Table 1. Of their 48 participants, 10 had the opposite result and showed a bias to the coin landing on the opposite side it started, and there were a handful of participants with a very severe bias, with one showing a bias of 60/40. So they key take away I think is not "51/49 bias of the same side you started with", but rather "everyone has their own individual bias when flipping a coin".

Given that, and given that each coin itself will also have its own intrinsic bias, then again the solution is the simple one I've outlined many times before - use a von Neumann debiasing approach, but with the additional caveat that you should start each flip from the same position (i.e. heads face up). That way any bias in either the coin or your technique is completely eliminated and you will always end up with a completely random result.

Topic: Are dices for generating seed words fair? - page 4. (Read 3342 times)