What stops people creating the same bitcoin address?

[rscholey]

I see many products that create wallets with new addresses.  But what is to stop some of those addresses from being the same? Could an address that matches one already in service be created?

[Pony789]

I see many products that create wallets with new addresses.  But what is to stop some of those addresses from being the same? Could an address that matches one already in service be created?

The chance for an address collision to happen is nonzero but extremely small, since there are a total of 2²⁵⁶ private keys and 2¹⁶⁰ valid bitcoin addresses. https://bitcointalk.org/index.php?topic=104461.0;all could help you understand it better how tiny the chance is.

[Possum577]

Technically yes, but the odds of it happening are astronomical... a 24+ plus key, using 10 numbers, 26 upper case letters, and 26 lower case letters as options. That's a lot of combinations.

[coinableS]

Very very large numbers prevent address collisions.
It really is difficult to comprehend how large these numbers are, and I'm not insulting you when I say comprehend, it's difficult for everyone. Once you go over a million it's hard for the mind to comprehend the effort needed to increase to the next order of magnitude.  The number of possible addresses is 2^160 or 1.4 quindecillion (http://www.wolframalpha.com/input/?i=2%5E160). For a perspective, if you assume a grain of sand has an average size and you calculate how many grains are in a teaspoon and then multiply by all the beaches and deserts in the world, the Earth has roughly seven quintillion grains of sand.

1400000000000000000000000000000000000000000000000 BTC addresses
7000000000000000000 grains of sand

The possibility of two of the same addresses being generated is nearly impossible since the pool is so large.

[Quickseller]

But what is to stop some of those addresses from being the same?

• Randomness
• An extremely large set of potential addresses that can be created
• The fact that if the most efficient technology possible (based on our current understanding of physics) were to somehow harvest all of the energy of the sun, all of the possible Bitcoin addresses would not be generated after a thousand years

 

[jacktheking]

I read there is as many Bitcoin addresses as the sands on the earth. Although the chances to generate the same Bitcoin address is small... everyone should take precaution by spreading their coins in multiple addresses.

[Kakmakr]

I read there is as many Bitcoin addresses as the sands on the earth. Although the chances to generate the same Bitcoin address is small... everyone should take precaution by spreading their coins in multiple addresses.

There is a video on youtube, from the Bitcoin network that use this <grain of sand> as a example, but they say that the sand on the earth and a few thousand other planets will not be enough to equal the math needed to calculate the Addresses that can be created from that algorithm.

I will search for it and post it here, when I have a bit more time.

I know something went wrong at Blockchain.info a while ago, and duplicate Bitcoin addresses where created due to the randomness of the generator not being random at all. <short explanation> The hacker who identified this, gave all the Bitcoins back to the users with these duplicate Bitcoin address & private key parings.

[christycalhoun]

Still, if you are so worried you can do test transactions to verify you control the address. It is unlikely though.

[Pony789]

I read there is as many Bitcoin addresses as the sands on the earth. Although the chances to generate the same Bitcoin address is small... everyone should take precaution by spreading their coins in multiple addresses.

There is a video on youtube, from the Bitcoin network that use this <grain of sand> as a example, but they say that the sand on the earth and a few thousand other planets will not be enough to equal the math needed to calculate the Addresses that can be created from that algorithm.

I haven't seen that video, but you are right that the number of grains of sand on Earth is nowhere close to the number of bitcoin addresses.

According to http://www.quickanddirtytips.com/education/math/how-many-grains-of-sand-are-on-earth%E2%80%99s-beaches, there are 5.6x10^21 grains of sand on Earth.
According to https://www.quora.com/Are-there-more-stars-than-grains-of-sand, there are 10^24 grains of sand on Earth.
According to http://www.npr.org/sections/krulwich/2012/09/17/161096233/which-is-greater-the-number-of-sand-grains-on-earth-or-stars-in-the-sky, there are 7.5 x 10^18 grains of sand.
No idea which of these estimates are accurate, but let's take the largest one, ie 10^24.

On the other hand, there are 2^160 or 1.46x10^48 bitcoin addresses, which is 1,460,000,000,000,000,000,000,000 times larger the the number of grains of sand.

[norzgonz]

But what is to stop some of those addresses from being the same?

• Randomness
• An extremely large set of potential addresses that can be created
• The fact that if the most efficient technology possible (based on our current understanding of physics) were to somehow harvest all of the energy of the sun, all of the possible Bitcoin addresses would not be generated after a thousand years

 

All these points are based on probability.
But I want to know how sure a repeated bitcoin address is prevented?
I knew bitcoin address can be generated in offline too.
I guess a time based and System ID or/and IP based coding must be there to prevent a repeated address.

[shorena]

-snip-
All these points are based on probability.
But I want to know how sure a repeated bitcoin address is prevented?
I knew bitcoin address can be generated in offline too.
I guess a time based and System ID or/and IP based coding must be there to prevent a repeated address.

What you say is: I know dice are random, but I want to know what prevents people from rolling a 6 trillion 50 times in a row, there must be some system in place to prevent that.

Edit: fixed with more realistic numbers, thanks to odolvlobo below.

[altcoinhosting]

I would worry a lot more about things like brainwallet keys from users that used really simple passphrases... They can be generated twice by different users, but a random private key, chances are soooooo small 

[Quickseller]

But what is to stop some of those addresses from being the same?

• Randomness
• An extremely large set of potential addresses that can be created
• The fact that if the most efficient technology possible (based on our current understanding of physics) were to somehow harvest all of the energy of the sun, all of the possible Bitcoin addresses would not be generated after a thousand years

 

All these points are based on probability.
But I want to know how sure a repeated bitcoin address is prevented?
I knew bitcoin address can be generated in offline too.
I guess a time based and System ID or/and IP based coding must be there to prevent a repeated address.

There is nothing that will prevent the same address from being generated more then once. Assuming that your private key is generated in a truly random way then the chances of this happening are nearly zero.

If the method that you use to generate private keys is somehow flawed (eg you use a weak random number generator) then the chances of generating the same private key as someone else would increase.

You need to remember that it is always possible that one person may wish to use the same address across multiple computers/locations, and that the network does not actually do anything when a new address is generated (addresses can be generated offline).

[Velkro]

The chance for an address collision to happen is nonzero but extremely small, since there are a total of 2²⁵⁶ private keys and 2¹⁶⁰ valid bitcoin addresses. https://bitcointalk.org/index.php?topic=104461.0;all could help you understand it better how tiny the chance is.

far more common is to random number generator is faulty, so its generating same addresses
happened couple times before

[odolvlobo]

-snip-
All these points are based on probability.
But I want to know how sure a repeated bitcoin address is prevented?
I knew bitcoin address can be generated in offline too.
I guess a time based and System ID or/and IP based coding must be there to prevent a repeated address.

What you say is: I know dice are random, but I want to know what prevents people from rolling a 6 a trillion times in a row, there must be some system in place to prevent that.

You are exaggerating. 2¹⁶⁰ is approximately equal to 6⁶², so the real probability is the same as rolling a 6 62 times in a row. But that is the probability of generating a particular address. The chances of generating any address that someone has a private for is more like 6⁵⁰, give or take a few orders of magnitude.

[shorena]

-snip-
All these points are based on probability.
But I want to know how sure a repeated bitcoin address is prevented?
I knew bitcoin address can be generated in offline too.
I guess a time based and System ID or/and IP based coding must be there to prevent a repeated address.

What you say is: I know dice are random, but I want to know what prevents people from rolling a 6 a trillion times in a row, there must be some system in place to prevent that.

You are exaggerating. 2¹⁶⁰ is approximately equal to 6⁶², so the real probability is the same as rolling a 6 62 times in a row. But that is the probability of generating a particular address. The chances of generating any address that someone has a private for is more like 6⁵⁰, give or take a few orders of magnitude.

Thanks, I fixed it.

[jaberwock]

A good hash function + randomness, so will be highly unlikely to generate the same address(not feasible in any reasonable amount of time using any feasible resources).

And even if you find a collision, will be highly unlikely that you'll find an address that has some decent amount of BTC

[Amph]

it may be possible in the future(very far away future) if something new emerge from the scienze or universe, for example the dark matter is still unknown, you don't know its interaction with something else

still collisions are far away from being impossible, so who know maybe it could happen one day

[odolvlobo]

it may be possible in the future(very far away future) if something new emerge from the scienze or universe, for example the dark matter is still unknown, you don't know its interaction with something else

still collisions are far away from being impossible, so who know maybe it could happen one day

That's a silly thing to write. The odds of an address collision are less than the odds of two people selecting the same molecule of water.

[Reynaldo]

I read there is as many Bitcoin addresses as the sands on the earth. Although the chances to generate the same Bitcoin address is small... everyone should take precaution by spreading their coins in multiple addresses.

I try to avoid here to get +1 posts but this guy is just trolling, can we proceed to report this guy? "everyone should take precaution by spreading their coins in multiple addresses" this is the most retarded thing that you can say, before spreading FUD you should go read about something or at least edit the post after the information was posted

it may be possible in the future(very far away future) if something new emerge from the scienze or universe, for example the dark matter is still unknown, you don't know its interaction with something else

still collisions are far away from being impossible, so who know maybe it could happen one day

That's a silly thing to write. The odds of an address collision are less than the odds of two people selecting the same molecule of water.

you are really silly to think that "the dark matter is still unknown" instead of reading internet's trash, buy some physics books..