Bitcoin Forum

I did a small experiment, I copied the wallet.dat and put it on another offline computer. I was able to send the same bitcoins twice! How can this be fixed?

you could send them but was the transaction confirmed?

Once one is confirmed, the other can't be if I'm not mistaken. Is it decided by which client is more updated?

phone apps can be produced that generate a private key using the IMEI number of a phone. these app's could become the more secure apps that are trusted to send funds without confirms as the private keys wont work unless used on that specific phone. thus if it is confirmed on the phone then sending it somewhere like starbucks, they can instantly see that it cant be double spent.

Not sure - I think it is possible to change the IMEI on some phones. That is the way some stolen phones get a new identification.

Ok, guys, IMEI? please!

OP, which client are you talking about?
Generally sending coins twice should be resolved automatically, so as soon as both clients see which transaction went through, the one that violates this, will be "forgotten". No issue here. Just bring you computer online.

You can send as many times as you want. Only one of them (at most) would be confirmed.

It can be fixed by you coming back here and providing an update. Specifically, you could write an essay titled "Why I am not rich yet?".

To help you get started, here is a hint: you were not able to send the same bitcoins twice, at least not any more than you would be able to send them twice by yelling "HERE, I SENT 'EM!!" from your balcony twice. Bitcoin transactions are verified, confirmed, timestamped, and entered into the ledger collectively by a p2p network.

TOB, not you again.

This one made me laugh.  :D

Well, you now have two wallet.dat files which are out of sync.  Bitcoin-Qt/bitcoind wasn't designed to work this way (running two copies of the Client with the same wallet.dat).  As a result, the two wallet.dat files are now out of sync.

In short, don't do this.   It doesn't affect the blockchain, but it will give you grief and multiple copies of a wallet getting out of sync can potentially cause you to end up with financial loss.

To resolve this ... you will have one Client in which the transaction confirms.  In the other instance you will have a transaction that won't confirm (presuming both are attempting to spend the same funds).  

So, if the balance on the one with the confirmation is correct, then simply discontinue use of the other instance -- the one with the transaction that will never confirm.

You tried double spending.
Be careful because the network might mark you as a scammer, and you will have troubles (not sure)

niko has a run of great posts lately.

Don't put too much energy into answering him, TheoryOfBitcoin is likely to be a troll...

This is untrue.

Agreed.  I'm surprised his ignore button isn't yellow yet.  I suspect it will be before long.

Looking at his other 13 posts he is just not this ignorant, so TheoryollOfBitcoin.

I figured he was trolling if a newb like myself new it would only confirm once.

http://pegfitzpatrick.com/wp-content/uploads/2012/08/trolls-einstein1.png