Bitcoin Forum

If person A generates a bitcoin wallet address and has say 2 bitcoins and person B generates the same address, can Person B spend Person A's bitcoins?

Yes he can. There are a lot of threads though explaining that this is not something that will happen in the next million years...

Chances for that to happen are extremely small.

i belive it has happend once and only once so far. im not sure if it was true or not but there where threads about it some time ago.. anyhow if you generated 1000 bitcoin addresses a second for a million years i think it works out at a 50% chance so yeh not very likely

This would be called a "collision" and is highly unlikely.

Keys are 256 bit in length and are hashed in a 160 bit address.(2^160th power) Divide it by the world population and you have about 215,000,000,000,000,000,000,000,000,000,000,000,000 addresses per capita.(2.15 x 10^38)

Nope, you need much more than that. If you generated 1000 bitcoin addresses a second for a million years you would have still about 0% chance. Oterwise it could be done just on one GPU in one year, when I generate vanity addresses it tries 20 million addresses per second

I don't think you have the math correct.

I think its closer to 1,000,000,000,000,000,000,000,000,000,000,000,000,000 years.

The odds are astronomical, something like there being more bitcoin addresses than atoms in the universe. A very large number.

sorry i was just going off what i thought id heard might have been a trillion addresses a secound for a trillion years :D

Possibly trillion on the long scale (1 trillion = 1,000,000,000,000,000,000).  I don't think trillion on the short scale (1 trillion = 1,000,000,000,000) is enough.

Yes, but the chance is like that Sylvester Stallone come to my house and steal a xbox controller battery.

A coffee cup falling through a table quantum mechanically has a higher chance...

The chances of 2 people generating the same private key is very, very, very, very slim.

Never happened and never will happen in our lifetime or in anyone's lifetime for that matter. The sun will become a red giant and fry earth long before that.

That being said there are some terrible numbers in this thread mostly because people cant tell the difference between collision and finding out the key of a specific address.

And how would one prove it really happened ?
I mean it is much easier to hack computer and stole private key to your Bitcoin and you cant say what of the 2 happened...

Yes. Very unlikely. But shared addresses happen all the time when two people share the same wallet.dat. So for example you could have 10 BTC on one machine's wallet and 10BTC on another machine's wallet. But in reality you only have 10 BTC in total.

The specific number of hashes you'd have to generate to have a 50% chance of a collision with a 160 bit (RIPEMD-160) hash (assuming that the results of RIPEND-160 are evenly distributed) are 1.42x10²⁴

Therefore, it looks like a trillion (on the short scale) per second for a trillion (on the short scale) years (3.15X10³¹) would be enough after all.

As a matter of fact, if you could continuously generate and compare a trillion (on the short scale) addresses per second non-stop, you'd have a 50% chance after only 1,000,000 years.

Note that there is more involved in generating addresses than just a hash.  You have to generate a private/public keypair, then generate a SHA256 hash, then generate a RIPEMD-160 hash, then compare the result to ALL the results you've generated so far.  And with an ever growing number of results to compare to, it may be difficult to continuously complete the task a trillion times per second.