why cant people spend other's money

[ebyccc]

I am quite new to bitcoin, still reading the guide, and being puzzled about this. For example, if somebody just create one million private keys and run one million wallet programs at the same time, he would much likely receive some output that paid to one or more private keys (addresses maybe) he generated, and thus steals others' money
Could this be a problem?

[OmegaStarScream]

It more likely to get the same address as someone else If you are using Brainwallet instead of letting your Desktop/web wallet generates the wallet randomly .
Read this for more info : http://bitcoin.stackexchange.com/questions/7724/what-happens-if-your-bitcoin-client-generates-an-address-identical-to-another-pe

[justspare]

I really have no idea. I never thought of that actually. But I am pretty sure that it is very hard for you to get the same address as someone else. Maybe I am wrong and this could be a huge problem.

[ebyccc]

I really have no idea. I never thought of that actually. But I am pretty sure that it is very hard for you to get the same address as someone else. Maybe I am wrong and this could be a huge problem.

yes this maybe not a problem, after some calculation I find that the thief has to generate on average 7*10^41 keys to make a successful theft

[Pursuer]

you are talking about something called address collision which means someone accidentally created an address that was created before.
read this article on wiki: https://en.bitcoin.it/wiki/Technical_background_of_version_1_Bitcoin_addresses#Collisions
in short 1 million is not even a big number in comparison

[topiOleg]

I really have no idea. I never thought of that actually. But I am pretty sure that it is very hard for you to get the same address as someone else. Maybe I am wrong and this could be a huge problem.

yes this maybe not a problem, after some calculation I find that the thief has to generate on average 7*10^41 keys to make a successful theft

Thats very small likelihood, and even if collision ever happens sometimes, it should be empty previously used address or some dust Bitcoin amount. There are only about under million Bitcoin address worth non Dust amount, yet about 100 million Bitcoin address used already

[Lauda]

For example, if somebody just create one million private keys and run one million wallet programs at the same time, he would much likely receive some output that paid to one or more private keys (addresses maybe) he generated, and thus steals others' money

I'm not sure what you exactly mean by this. If you are talking about possible collisions, then that is statistically impossible (highly improbable*):
There are 2^160 possible addresses (IIRC), which equals to: ~1,460,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000.

Vanitygen can produce 20 million keypairs per second.  Lets say you build a super ASIC on 12nm (4 generations ahead of current tech) process that could create, validate, and steal one trillion keypairs per second (1 TK/s). That would be about 50,000x more powerful than faster GPU today.  Lets also say you built a thousand of them and ran them continually with no downtime 24/7/365.   In 1 year you could brute force 3*10^28 possible addresses.  
If there are 1 quadrillion funded addresses you would still have a ~1% chance of colliding with a random funded address in the next 1,000 years.

People just aren't aware of how huge these numbers are.

[avikz]

I don't think that duplicate wallet address is virtually possible. I think everything is taken care by blockchain itself.

However, you can use your email address instead of giving away your wallet id if you are holding account with coinbase. It will save your from your money being stolen.

[shorena]

I don't think that duplicate wallet address is virtually possible.

Its impossible.

I think everything is taken care by blockchain itself.

No, if anyone else should ever gain access to your private key(s). Your coins are gone. Its just so unlikely that this happens by chance (or brute force) that we can reasonably call it impossible. There are no defenses against that in the code though.

However, you can use your email address instead of giving away your wallet id if you are holding account with coinbase. It will save your from your money being stolen.

Unless, its coinbase that is stealing your coins. If you do not hold the private key, you have no bitcoin. All you have is a promise from some company you probably know less about than the store around the corner you get your food from.

[calkob]

I am quite new to bitcoin, still reading the guide, and being puzzled about this. For example, if somebody just create one million private keys and run one million wallet programs at the same time, he would much likely receive some output that paid to one or more private keys (addresses maybe) he generated, and thus steals others' money
Could this be a problem?

The simple answer is no watch a couple of good you tube videos that explain why it is mathmatically impossible in your life time to find another private key.....

[ronald98]

I don't think that duplicate wallet address is virtually possible.

Its impossible.

...

It's so unlikely that it's as good as impossible. To calculate the same address and private key as someone else is more unlikely than getting hit by lightning at 12 noon for six consecutive days, then winning the lottery on the 7th day. If you search bitcointalk you will find countless threads by people who lost their private key for their Bitcoin wallet and want to know how to get their Bitcoins back. The short answer is without their private key they can't.

[tyz]

To be serious: one million accounts is not much compared to 2^32 possible accounts. So, it is very unlikely to spend other's money by guessing or calculating the private keys of accounts. A lot of people tried this before without success. This is why Bitcoin is considered very save.

[rapazev]

Its impossible.

Not impossible, just highly improbable 


\--
And, imagine that happen, you did duplicate a wallet... you still need to be lucky enough to duplicate a whale wallet... someone who receive and send a lot of bitcoins.

[franky1]

I am quite new to bitcoin, still reading the guide, and being puzzled about this. For example, if somebody just create one million private keys and run one million wallet programs at the same time, he would much likely receive some output that paid to one or more private keys (addresses maybe) he generated, and thus steals others' money
Could this be a problem?

if you could make 1million addresses in a minute.. then you will have all the possible bitcoin addresses available when.. wait for it.

your great great great great great great great great great great great great great grand children have become great great great great great great great great great great great great great grand parents.

so goodluck

there are more bitcoin addresses available than grains of sand on the planet

[coinzat]

the percentage that someone may generate a used address by chance is very very low and it is impossible to make it with vanitygen. but it you are afraid, you can move your funds from address to another from time to time

[odolvlobo]

To be serious: one million accounts is not much compared to 2^32 possible accounts. So, it is very unlikely to spend other's money by guessing or calculating the private keys of accounts. A lot of people tried this before without success. This is why Bitcoin is considered very save.

I don't know where you get "2³² possible accounts", but 1 million is ¹/₄₂₉₅ of 2³². Perhaps you meant 2¹⁶⁰. Your laptop can easily test 2³² private keys in a day.

[Soros Shorts]

I don't think that duplicate wallet address is virtually possible.

Its impossible.

As long as you don't use some broken random number generator to generate your private keys. Or even worse, manually pick a private key value of say 0x1.

[cyberguy]

I am quite new to bitcoin, still reading the guide, and being puzzled about this. For example, if somebody just create one million private keys and run one million wallet programs at the same time, he would much likely receive some output that paid to one or more private keys (addresses maybe) he generated, and thus steals others' money
Could this be a problem?

A private key is a 256 bit binary number. When written in hexadecimal this comes to a 64-digit hexadecimal number, which in decimal is approximately 1.158 x 10^77. Each private key will produce a unique public key and corresponding bitcoin address. So there are 2^256 possible combinations of private key, public keys and bitcoin addresses.

To get an idea of the numbers we are dealing with consider the following.

The world's fastest super computer is currently capable of performaing 33.6 quadrillion (33.6 x 10^15) calculations per second. Even if we assume that this makes it possible to check one private key per calculation (the actual number will be less since checking whether a particular private key agrees with a given bitcoin address will need much more than one calcultion), it would need 3.45 x 10^60 seconds or 1.1 x 10^53 years to try all possible private keys. So to try and steal bitcoins that are at a particular address by trying all possible addresses, though theoritically possible is computationally infeasible.

[Kakmakr]

There are some brilliant videos on Youtube explaining this, if you just search for the Math behind Bitcoin. In one video they compared private keys to the sand on earth and said, if you took all the sand on all the planets in our galaxy, then you will still not cover all the combinations that could be created with Bitcoins algorithm.

I think it is a bit extreme, but it gives you an idea what the probability will be for this to happen.

[Amph]

because your example is no where near the maximum number of private key and public key in existence, type 2^256 and see how big is that number

it maybe be possible in a very distant future, 1000 or 10k year from now, where new unprecedent technology are discovered