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Author Topic: Has anyone ever cancelled a BTC transaction after 1 confirmation?  (Read 2361 times)
doof
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April 24, 2014, 10:04:54 AM
 #21

Is this even possible?

Thanks in advance  Cool
Not possible, once it's confirmed it's in the blockchain forever.  That's the beauty of Bitcoin Smiley

Not exactly true.  If it is confirmed, but that block is part of a fork and the competing block wins, then it will become "unconfirmed" *if* it doesn't also appear in the competing fork.
Kazimir
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April 24, 2014, 10:49:51 AM
 #22

You can't even cancel a BTC transaction after ZERO confirmations.

In theory, there's no difference between theory and practice. In practice, there is.
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Lauda
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April 24, 2014, 02:25:37 PM
 #23

virtually impossible, same concept as double spending
Yet it is possible. Please do more research or just read the damn replies in the thread!

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atc1
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April 24, 2014, 02:28:29 PM
 #24

Is this even possible?

Thanks in advance  Cool

It is possible, but it is difficult, expensive, and unreliable.

If you have enough hashpower, you could create a transaction that spends some bitcoins to another address that you own, and not broadcast that transaction.

Then you could mine a block with that transaction on top of the current blockchain.

As soon as you successfully mine a block, you could broadcast a different transaction that spends the same inputs sending the bitcoins to a merchant, and NOT broadcast the block you just solved.

While the network is working on confirming your transaction into a block that will compete with your block, you continue mining on top of your block.

Eventually, the network will solve a block with your transaction in it and the merchant will see 1 confirmation. You continue to mine on top of your block instead of on top of the network's block.

If you have enough hash power and are lucky enough to mine another block before the rest of the network does, you broadcast your two blocks.

There are other possible attacks as well, but none of them are cheap, easy, and 100% reliable.

Since your two blocks create a longer blockchain than the current blockchain that has only added one block, the entire network switches to your blockchain and the 1 confirmation transaction to the merchant disappears (since it competes with your first transaction that now has 2 confirmations).

The more confirmations you have, the more difficult, expensive, and unreliable an attack like this is.

You know,there's already a service which offers such a thing for transactions with 0 confirmations. I'm not sure about the one with 1 confirmation as it would be a lot harder,but yes,the possibility is almost 0.

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April 24, 2014, 02:35:15 PM
 #25

Is this even possible?

Thanks in advance  Cool

It is possible, but it is difficult, expensive, and unreliable.

If you have enough hashpower, you could create a transaction that spends some bitcoins to another address that you own, and not broadcast that transaction.

Then you could mine a block with that transaction on top of the current blockchain.

As soon as you successfully mine a block, you could broadcast a different transaction that spends the same inputs sending the bitcoins to a merchant, and NOT broadcast the block you just solved.

While the network is working on confirming your transaction into a block that will compete with your block, you continue mining on top of your block.

Eventually, the network will solve a block with your transaction in it and the merchant will see 1 confirmation. You continue to mine on top of your block instead of on top of the network's block.

If you have enough hash power and are lucky enough to mine another block before the rest of the network does, you broadcast your two blocks.

There are other possible attacks as well, but none of them are cheap, easy, and 100% reliable.

Since your two blocks create a longer blockchain than the current blockchain that has only added one block, the entire network switches to your blockchain and the 1 confirmation transaction to the merchant disappears (since it competes with your first transaction that now has 2 confirmations).

The more confirmations you have, the more difficult, expensive, and unreliable an attack like this is.
Your knowledge always seems to amaze me. This is a bit complicated to do, and not worth it like you just said.

How do I vouch for a Bitcoin expert badge (https://bitcointalk.org/index.php?topic=392808.msg4233210#msg4233210) for Danny ? I have seen multiple times that Danny is a true expert of the Bitcoin protocol. So, I guess, he deserves the title.


DannyHamilton
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April 24, 2014, 04:11:31 PM
 #26

How do I vouch for a Bitcoin expert badge (https://bitcointalk.org/index.php?topic=392808.msg4233210#msg4233210) for Danny?

You don't.  Only a core developer or other "Bitcoin Expert" is allowed to recommend that someone receive the "Bitcoin Expert" badge.

I have seen multiple times that Danny is a true expert of the Bitcoin protocol. So, I guess, he deserves the title.

Titles don't mean much to me.  My advice and assistance stand on their own merits.
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April 24, 2014, 04:17:01 PM
 #27

Is this even possible?

Thanks in advance  Cool
Not possible, once it's confirmed it's in the blockchain forever.  That's the beauty of Bitcoin Smiley

We now have miners with hundreds of thousands of dollars of equipment which run it off a raspberry pi. Who send their coins directly to coinbase to be sold. Who have never used a Bitcoin client of any kind (except for the coinbase webwallet), certainly not a full node, and they have no concept of why they'd want to.  The name they trust most in mining is operator of their chosen pool— who could be robbing them blind, but maybe isn't— who has a financial interest to the tune of— say— >$700,000/month in keeping miners on their pool, and who tells them they don't need to worry about things, and who is believed because far too many people— including you— overly fixate on "51%" and ignore the fact that someone who controls 25% hashpower can reorg 6 confirms with 5% success or 2 with 31% success.

bold is mine

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April 24, 2014, 04:21:43 PM
 #28

It's not possible when it has at least one confirmation your money is fully gone, if it doesn't get any confirmations for a long time i think It would get back to your wallet, at least someone said that to me.
sickpig
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April 24, 2014, 04:26:17 PM
 #29

It's not possible when it has at least one confirmation your money is fully gone, ...

false.

please read previous posts on this thread to get some hints on why it's possible.

Bitcoin is a participatory system which ought to respect the right of self determinism of all of its users - Gregory Maxwell.
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