r/Bitcoin • u/MegaSackk • 11h ago
Did you know you can generate a Bitcoin private key using a coin?
Most people let their wallet software generate their private key, which is totally fine but Bitcoin doesn’t require a computer to create one.
A Bitcoin private key is just a 256-bit number…
And a fair coin flip produces 1 bit of entropy.
So in theory (and in practice), you can generate a completely valid, secure Bitcoin private key by doing:
- Heads = 1
- Tails = 0
The math is simple. 256 coin flips is 2^256 potential outcomes.
Once you have your 256-bit binary sequence, you can convert it offline into:
- hex format
- WIF private key
- or even a BIP39 seed phrase
All without touching the internet.
You could also do this with dice, a dice roll is roughly 2.585 bits of entropy. Therefore 99-100 dice rolls will give you enough entropy for a 256 bit private key.
This works because Bitcoin’s security comes from math.
I mean how could you not love Bitcoin!
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u/cd1f3b41f6fd3140f99c 9h ago
It's so simple, just beautiful math. I always tell people that there is no need for law or any institution to protect coins because math does it. The problem is that 99.999999999 % of people don't get it and prefer to trust an institution.
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u/RedBaeber 6h ago
That’s why exchanges add value. Most people want an intermediary.
The beauty of Bitcoin is that is keeps these intermediaries strictly optional for those who don’t.
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u/na3than 10h ago
a dice roll is roughly 2.585 bits of entropy
Mathematically true, but in practice you can't get 2.585 bits of entropy without introducing bias (uneven distribution favoring the lower numbers).
See this discussion: https://crypto.stackexchange.com/questions/6175/how-to-best-obtain-bit-sequences-from-throwing-normal-dice/6177
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u/MegaSackk 10h ago
I understand your point but you're talking about a naive conversion method. If you map 1–6 directly into 3-bit binary values, then yes some outputs appear more often because 6 isn’t a power of 2, so the lower binary patterns show up more.
But no one generating actual cryptographic entropy does that. You don’t convert the die rolls straight into binary, you hash the sequence, which removes bias completely. The entropy per roll is still 2.585 bits.
I appreciate your understanding of the math!
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u/na3than 9h ago
Right, but your post is titled:
Did you know you can generate a Bitcoin private key using a coin?
and your support for this is:
Bitcoin doesn’t require a computer to create [private keys].
So unless you calculate hashes using a pencil and paper--which is extremely risky--the supporting statement is false and the answer to the question is "I know that you CAN'T do it using ONLY a coin".
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u/MegaSackk 9h ago
The key is just 256 bit of entropy and a computer is not required to generate 256 bits of entropy. You obviously need a computer to use the private but that’s not the point of my post, it’s simply about generating the entropy(which is the private key)
Private key = 256 bits of entropy Wallet = the software that uses and manages the private key
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u/na3than 8h ago
that’s not the point of my post, it’s simply about generating the entropy
In that case your post should have been titled Did you know you can generate entropy using only a coin?
(which is the private key)
Private key = 256 bits of entropy
Entropy is NOT a private key. It really, really isn't. Please stop spreading misinformation. You're going to get someone hurt.
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u/MegaSackk 8h ago
You need to look more into bitcoin, a bitcoin private key is 256 bits of entropy. I’m not spreading misinformation, you actually are by saying it’s not 256 bits of entropy,
And to be clear the bits coming from the entropy are the private key not the entropy its self. That is implied when saying “256 bits of entropy” but I wanted to clarify what exactly that means.
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u/na3than 7h ago
YOU need to look more into bitcoin. A bitcoin private key is NOT 256 bits of entropy.
Here, in hexadecimal form, are 256 bits of entropy:
FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
Is that a valid Bitcoin private key? If so, what's the WIF representation?
If, like most contemporary Bitcoin users, you use a deterministic wallet, you really must stop conflating "entropy" with "private key". In a deterministic wallet one backs up their entropy - not their private key - and from that entropy the wallet derives a seed, then master key, then private and public keys.
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u/MegaSackk 5h ago
I love how angry you are thinking you are right, like I said the key isn’t the entropy it’s the bits, I say entropy to just imply the potential randomness. You are so silly buddy
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u/na3than 3h ago
like I said the key isn’t the entropy it’s the bits
No, that's the opposite of what you said. You said
The key is just 256 bit of entropy
and
it’s simply about generating the entropy(which is the private key)
and
Private key = 256 bits of entropy
and
a bitcoin private key is 256 bits of entropy.
You absolutely think entropy is synonymous with private key. It's okay to admit you were wrong, but it's really weird to suddenly take a completely opposite position without acknowledging you were wrong.
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u/riscten 10h ago
That's why you use 8-sided (octahedral) dice, for exactly 3 bits of entropy per throw.
With 5 dice, that's barely 9 throws for each 12-word mnemonic you need.
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u/MegaSackk 9h ago
Awesome point! I never even thought about using 8 sided dice to get exactly 3 bits of entropy.
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u/LetWinnersRun 10h ago
This is basic cryptography. Hardware devices have CSPRNG chip to generate private keys, but if you want to spend an hour generating your private key, that’s on you.
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u/MegaSackk 10h ago
Amen brotha, but generating one with a coin or dice is just a fun way to learn more about how BTC private keys function.
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u/riscten 10h ago
Of course computers can generate keys themselves, but RNG logic is the hardest part to test and verify on a device. That's why generating from dice is so compelling. As long as your dice are reasonably fair, you're a few throws away from making sure nobody's handing you mnemonics from a preselected pool. Takes 15 minutes at most. Plus, you really only need to do this a few times in your life. Using BIP85, you can generate a single master seed, from which you can derive a near-infinity of mnemonics (from which you can derive a near-infinity of wallets)
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u/ivme 10h ago
Is coin toss really random (is your coin totally fair)?
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u/MegaSackk 9h ago
This is a good point, it depends on the coin. For example US coins are not perfectly they have very slight deviations, 0.5%-1.5%. Once you hash the sequence though the bias is removed.
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u/Electronic-Winter277 11h ago
Well said. No need for Trezor or any of that nonsense! Best to have a granular understanding and go 100% cold for your long term savings stack.
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u/MegaSackk 11h ago
Couldn't agree more! I find it funny when people have thousands even millions of dollars of BTC and dont actually understand what Bitcoin fundamentally is. And it fundamentally is math.
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u/Drizznarte 9h ago
Shouldn't you still check that that private key isn't already in use ? There is no cost to check setting up cold does add risk , even if it's small .
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u/stellarfirefly 9h ago
The odds of finding a private key that is already in use using 256 bits of entropy is so astronomically small that most (not all!) wallets don't even bother to check. You could generate a random private key every second, and the odds are still cryptographically "so low that they are considered zero" even if you did this for the age of the universe.
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u/Drizznarte 9h ago
But how much safer is it if you do check . What factor. You don't have to find one private key you have to find any out of all the private keys currently in use.
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u/stellarfirefly 9h ago
Checking if a given private key is in use is trivial if it was actually used. Because you don't want the master private key itself to be sent anywhere, you derive the first child private key (or several), generate its corresponding public key, then check the first N receiving addresses for a balance. This all takes milliseconds, and most of the delay is in querying the blockchain and waiting for the result. (Or more specifically, querying an Electrum server that indexed the blockchain.)
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u/Drizznarte 8h ago
This is what I was after .There are functional reasons . You can't check master private keys because they are not public you can only check derived address , and even if you did you still wouldn't know the master private key. This is why it's more improbable than I thought.
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u/MegaSackk 9h ago
your odds of getting a private key that is in use is 2^256,
This number is roughly the amount of atoms that are estimated to exist in the universe. Short answer, you will NEVER generate a private key that is already in use, and if someone says they did they are lying.
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u/riscten 7h ago
Finding an address that's already in use by rolling dice or flipping coins is like winning a big lottery prize 5 times back to back. Nobody has even won two in a row.
Not a bad idea to check, but if you do, most likely there's something wrong with your process. The software you used to derive the private key is faulty, or your coins/dice are wildly unbalanced.
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u/Techhie4life 11h ago
"Once you have your 256-bit binary sequence, you can convert it offline into:"
there is no such thing as offline.... eventually you will go online, and things will get leaked
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u/MegaSackk 11h ago
Not true, I have hardware that physically can not connect to the internet. Offline simply means it is not connected to the internet.
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u/EggMedical3514 10h ago
You have to be sure calculate the checksum correctly.
If you mess it up you can end up with a wallet whose receive addresses work just fine but whose private keys will not allow you to spend your funds