I generated an address that already exists

[marcus_of_augustus]

Are you *sure* you didn't own that address already?

If not, it is VASTLY more probable you (and however generated this address before) just unearthed a bug in bitcoin's PRNG. Could you give more details - which OS and OpenSSL you have installed?

I find it *extremely* hard to believe you actually caused a collision. Not now, not in a 1000 years.

This.

Bad PRNG is more likely than collision. And we have had at least one corrupted RNG de-bugs thrown up by Bitcoin already, so it's got form.

OpenSSL on linux has had issues with generating weak keys in the past http://perimetergrid.com/wp/2008/05/17/ubuntudebian-crng-cracked-ssh-vulnerable/ .... and also it has been mentioned that introducing compromised code to produce weak keys via bad RNGs is an attack used by the spooks (for communication interception).

How well can OpenSSL ECC keys generation really be trusted? Does it depend on version of OpenSSL, use of underlying RNG, OS, etc? Is anyone testing this for bitcoin specific key generation?

(That whole crap fight over ECC not going into RH-derivative linux OpenSLL module makes me smell smoke ... maybe it was never about the patent non-problem?)

Edit: https://www.schneier.com/blog/archives/2008/05/random_number_b.html

Back when the NSA was routinely weakening commercial cryptography, their favorite technique was reducing the entropy of the random number generator.

History doesn't repeat but it sure does rhyme sometimes ...

[Jabbatheslutt]

Wasn't there a reward being offered to the first person to do this?

[JakeGold]

Couldn't I hypothetically create a script that systematically generates bitcoin addresses from the pregenerate pool and have the script lookup the generated address to see if the wallet is active with a balance then choose to spend this into a new wallet address?

It's called address trawling, but if you could wrap your head around how statistically improbable you are to find a wallet with a balance, even scanning millions of addresses per second, you'd go buy a lotto ticket instead.

[pand70]

It is so improbable that if it really happened it's alarming...

[rme]

That shouldn't be very probable, should it?

I used Bitcoin Qt client, pressed "New address" button to generate the address, sent a small amount to it and then checked on blockchain.info if the transaction was registered. To my surprise there are two other transactions made over a year ago using that address.

https://blockchain.info/address/1J9UHx3q9D1ZxZ5KwV8VGWJd7ksyTJtLTB

1. What OS and version of the client are you using? Could be a previously unknown bug in the random number generator.

2. Also, verify that you do own the private key to that address. Try to send that 0.1 BTC to another address of yours.

This, please verify the ownership.

[marcus_of_augustus]

Yep, looks like he owns it ... shit this is not good for Bitcoin Qt

[nwfella]

If true talk about no bueno...no bueno whatsoever!

[flatfly]

A coredev should look into this ASAP...

[jackjack]

Bad PRNG or user error
/thread

[Valerian77]

Finally it means that two address owners share the same address with different private keys. Then where are tansfers going to ?

[Rannasha]

Finally it means that two address owners share the same address with different private keys. Then where are tansfers going to ?

Anyone with a private key to a public address can spend coins transferred to that address. If two people hold a private key with the same public address, they can both spend the coins.

[jackjack]

Finally it means that two address owners share the same address with different private keys.

It doesn't mean this

[Abdussamad]

Guys could you please actually read the thread before posting? This is not a bad PRNG and NOT an address collision. This is a problem with the OP's wallet. It is recycling old addresses he has already used:

Open up the debug console (help->debug window->console), type in:

gettransaction 5aed0ce301ecd17b237be9bd0dda7fa8fb7e2eb7f453c2ca1f27de160a23c791

If it returns that old transaction then that key was already in the wallet when that transaction hit your client.

When I do this, I see some transaction info. I didn't restore my wallet.

Still, I don't understand what you mean by saying it's always an old address from the keypool.

When I press "New address" button does it generate a brand new address that no one used before?

[pand70]

Finally it means that two address owners share the same address with different private keys. Then where are tansfers going to ?

This is the one thing that can't happen.

[BlackBison]

Wow... didn't think it would ever happen

It didn't happen 

[frankenmint]

hmm this sort of act is what causes me to download the original qt client.  Now I'm on the hunt to build a script IDK about the statistics anymore.

[Valerian77]

Finally it means that two address owners share the same address with different private keys. Then where are tansfers going to ?

This is the one thing that can't happen.

Why not ? When I use https://www.bitaddress.org offline it can theoretically produce the same addresses. Is there anything preventing this szenario ?

[jackjack]

Finally it means that two address owners share the same address with different private keys. Then where are tansfers going to ?

This is the one thing that can't happen.

Why not ? When I use https://www.bitaddress.org offline it can theoretically produce the same addresses. Is there anything preventing this szenario ?

I can theoretically be teleported to Mars because of quantum tunelling
Would you respond "Why not ?Is there anything preventing this szenario ?" to someone telling me "it can't happen" ?

[BookLover]

My bet is Bitcoin-Qt went haywire and used a change address.   For whoever asked the keypool size is 100  but it can be changed by the user.

[dserrano5]

@OP: did your wallet balance increase when you generated that address? If not, then it's a previous address of yours. If it did, err, wow…