Confirmation wait time, problem or no?

[Blinken]

I have never done a transaction, but I have heard that confirmation wait times can be long, even hours. If true, this would seem to be a serious problem with Bitcoin. When I buy something I want to buy it immediately, not wait hours for the transaction to complete.

Also, I was thinking of buying some Bitcoins in person, but if the wait time is hours, then that means me and my counterparty will sit there in the goddamn conference room for hours and hours waiting for the transaction to complete.

I mean, what am I supposed to write in the email: "Dear sir, please meet me in Conference Room A of the Newton Bank of America where we will do the transaction. After the transfer is initiated we will then wait for it to complete and I will turn over the treasurer's check to you. I have reserved the conference room for 8:30 am in the morning, so that if we have to wait for 6 hours for the transaction to complete, the bank will still be open."

Yeah, I am sure that will go over well. What are we supposed to do? Play Nintendo while we wait for it to complete?

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[FreeMoney]

A confirmation takes an average of 10 minutes.

If you are doing business with someone you know for less than a life changing amount of money there is nothing to worry about.

If you really need to know it will be done immediately use a system with internal transfers.

[sebnow]

It probably takes about an hour to two hours to get 9 confirmations, which tends to be the normal amount required to verify a transaction by various websites. If you trust the person you can even allow 0 confirmations, or wait a while for a single confirmation (up to half an hour in my experience, it seems like the first one takes the longest).

[BitPay Business Solutions]

It is not a problem for any business that uses Bit-Pay.  We notify them (or their server) immediately when the payment is received with 0 confirmations.  We have never seen a double spend in over a year and over 5000 transactions.  But, for high dollar amounts, there's no problem in waiting for an hour to be sure. 

[FreeMoney]

It probably takes about an hour to two hours to get 9 confirmations, which tends to be the normal amount required to verify a transaction by various websites. If you trust the person you can even allow 0 confirmations, or wait a while for a single confirmation (up to half an hour in my experience, it seems like the first one takes the longest).

9? Never seen that.

[Sukrim]

Actually the standard is usually 6 confirmations and of course it takes the longest to get the transaction included in a block (= first confirmation) - after that every block mined is another confirmation.

[niko]

Has doublespend ever been executed successfully, even as an excercise?

[FreeMoney]

Has doublespend ever been executed successfully, even as an excercise?

I might remember wrong, but I think someone wrote a paper and was able to do it with low probability in favorable conditions (maybe poorly connected target node or something).

[BitPay Business Solutions]

Has doublespend ever been executed successfully, even as an excercise?

It may have been possible early on.  But as more nodes connect to the network every day, it becomes harder and harder.  for your average in-person purchase of lunch or dinner, it's just not worth it.  The computing power would be better spent mining and being productive. 

[niko]

Has doublespend ever been executed successfully, even as an excercise?

It may have been possible early on.  But as more nodes connect to the network every day, it becomes harder and harder.  for your average in-person purchase of lunch or dinner, it's just not worth it.  The computing power would be better spent mining and being productive. 

How would computing power help someone to doublespend? I thought the whole idea was to broadcast two transactions from the same address, and somehow interfere with the nodes so one of these eventually is orphaned (not included in the next block). Seems hard to pull off. 

All in all, I would accept everyday payments with zero confirmations, perhaps watching for a few moments for other transactions from the same address, and would accept even large payments after one or two confirmations.

Having said all this, I wonder if it's possible to doublespend by including a large fee with one of the transactions, so miners preferably include it in the next block?

[JoelKatz]

How would computing power help someone to doublespend?

In a Finney attack, you pre-mine a block with one transaction and announce the other transaction to mining pools. As soon as the other transaction is accepted with zero confirmations, you release the pre-mined block. It takes computing power to pre-mine that block.

I thought the whole idea was to broadcast two transactions from the same address, and somehow interfere with the nodes so one of these eventually is orphaned (not included in the next block). Seems hard to pull off.

That's too easy to defeat -- someone just watches the transactions as seen by the major mining nodes.

Having said all this, I wonder if it's possible to doublespend by including a large fee with one of the transactions, so miners preferably include it in the next block?

It's possible in theory, but miners haven't yet adopted a system of accepting newer, conflicting transactions in favor of older ones just for the higher fee.

[niko]

How would computing power help someone to doublespend?

In a Finney attack, you pre-mine a block with one transaction and announce the other transaction to mining pools. As soon as the other transaction is accepted with zero confirmations, you release the pre-mined block. It takes computing power to pre-mine that block.

I thought the whole idea was to broadcast two transactions from the same address, and somehow interfere with the nodes so one of these eventually is orphaned (not included in the next block). Seems hard to pull off.

That's too easy to defeat -- someone just watches the transactions as seen by the major mining nodes.

Having said all this, I wonder if it's possible to doublespend by including a large fee with one of the transactions, so miners preferably include it in the next block?

It's possible in theory, but miners haven't yet adopted a system of accepting newer, conflicting transactions in favor of older ones just for the higher fee.

Thanks, this helps!  If I broadcast two transactions at this moment, what determines which one will get into the next block? Assume the block is mined by deepbit, slush, or other major pool.

[JoelKatz]

Thanks, this helps!  If I broadcast two transactions at this moment, what determines which one will get into the next block? Assume the block is mined by deepbit, slush, or other major pool.

Whichever one was first seen by whoever mines the next block, assuming both transactions meet their requirement for inclusion. Theoretically, they could/should prefer to one with the higher transaction fee, but I don't believe anyone actually does this.

[Stephen Gornick]

Has doublespend ever been executed successfully, even as an excercise?

Attempts? Every day.

 - http://www.blockchain.info/double-spends

Successful?

You can approach 100% success at double spending on 0/unconfirmed, if the recipient is vulnerable due to the configuration (accepts incoming transactions, static IP).

  - http://eprint.iacr.org/2012/248.pdf
  - http://bitcointalk.org/index.php?topic=79090.0

When bitcoins are received and then lost because of a double spend, the transaction will usually eventually disappear, so there may have been successful 0/unconfirmed double-spends without the recipient even knowing (unless the change to the balance was detected.)   Even a successful vector76 attack leaves (where there was 1 confirmation) disappears, unless those coins too were spent.  This is what appears to have happened to a smaller exchange a few months back which discovered a spend transaction that would not confirm.  The reason that happened was because the input used was received just one block earlier and ended up being a double spend.

 - http://en.bitcoin.it/wiki/Double-spending

[aq]

Re: Confirmation wait time, problem or no?

No.

I have never done a transaction, ...

Maybe a good plan would be to actually just do a few. You know, it is not that hard, you can download the client, or use some web based wallet. Next head over to one of the faucets and get yourself some tiny amount of Bitcoins. Then do some transactions.

[Coinoisseur]

Internal transfers of coins on a service is the current "quick" solution, but wouldn't it be great if the built in confirmation (say basic 6+ confirms) process could occur very quickly. It is an internet currency after all.

Will be interesting once all the block rewards are mined and the network is persisting on transaction fees alone.

[Meni Rosenfeld]

Not going to be a problem.

The key point is that there are several ways to make a payment which is internal and thus instant, without having to trust an eWallet with your money. So you don't really have to sacrifice security for convenience.

[Coinoisseur]

You'll still be relying on some third party outside of the bitcoin network itself though. Not very different from the way credit transactions work now, but isn't one of the advantages of Bitcoin that it could be different and have the fast confirmations built into the system itself?

[Meni Rosenfeld]

You'll still be relying on some third party outside of the bitcoin network itself though. Not very different from the way credit transactions work now, but isn't one of the advantages of Bitcoin that it could be different and have the fast confirmations built into the system itself?

It's plenty different. Depending on the solution chosen (each with its own set of tradeoffs), you can do it without any third party. Even if there's a third party, then unlike CC they can't take your money whenever they want; the barrier of entry is very low, and so is the cost of providing the service, thus it will be much more competitive and efficient. There's minimal vendor lock-in, you don't even necessarily have to know who is providing the service, it can all be handled in the background by the software.

Raw Bitcoin transactions by design take time to be fully finalized; what makes it special is the powerful cryptography and scripting language which allows building flexible mechanisms on top of the raw transactions.

[sebnow]

It probably takes about an hour to two hours to get 9 confirmations, which tends to be the normal amount required to verify a transaction by various websites. If you trust the person you can even allow 0 confirmations, or wait a while for a single confirmation (up to half an hour in my experience, it seems like the first one takes the longest).

9? Never seen that.

Actually the standard is usually 6 confirmations and of course it takes the longest to get the transaction included in a block (= first confirmation) - after that every block mined is another confirmation.

Ah, I may have gotten confused; same number, different angle