How is this possible ? A Recent transaction suddenly becomes invalid

[jerry0]

How do you protect yourself again this then?


Make sure if someone send you btc, it need to have x amount of confirmations before you send them online money or give them cash?  So if its smaller amount, less confirmations?  What would be a good rule?


Anything small like ten and under, one confirmation


Anything one hundred and under, two confirmation


Anything like a thousand or so... 6 confirmation?


Anything higher than that.. 8 confirmation?


What about ppl who do like 5k or 50k usd transactions?  Those like ten confirmations?

[FinneysTrueVision]

https://www.blockchain.com/btc/tx/2f362caac5d3fa3a1cc586f5bdbb36bcfe6446cfc112eb1cb097d9669688204a

my wallet:  34Y9ZwTsT3H9zcnffirc2NM4XMkNmaLws6

You should have wait for at least 1 confirmation unless you trust the guy. This is what happened in my guess:

- The guy sent coins to an address A which he owns and the fees were less of course
- He then sent the coins from the address A, and the coins of the address A were not confirmed yet.
- He then gone back to the first transaction and rebroadcast the first transaction with a higher fee. And in rebroadcasting process, the tx you had with address A gone dropped.

That’s amazing way to cancel it however I did not know this can be done with the bitcoin chain as well ?
I mean I have done this in case of Ethereum transaction but never with bitcoin.

What is the exact principle behind this technique? Isn’t the transaction once broadcasted is captured with the nodes and it permanently sits there?

Nodes can't possibly see every single transaction that's being broadcast. A transaction is not permanent until it get confirmed.

[BitcoinGirl.Club]

How do you protect yourself again this then?


Make sure if someone send you btc, it need to have x amount of confirmations before you send them online money or give them cash?  So if its smaller amount, less confirmations?  What would be a good rule?


Anything small like ten and under, one confirmation


Anything one hundred and under, two confirmation


Anything like a thousand or so... 6 confirmation?


Anything higher than that.. 8 confirmation?


What about ppl who do like 5k or 50k usd transactions?  Those like ten confirmations?

There are no such things like for x amount of USD wait for y confirmations.

You protect yourself by waiting for at-least one confirmation. Very simple. If you have very large amount of coins like say 20 BTC or more then wait for six confirmation. Don't complicated it or over think it.

[Pmalek]

@nc50lc and @HCP

I always thought that an RBF transaction can only spend the same UTXO with higher fees to the same address as the original transaction, not a new one like in OPs case. What is the success rate for such a double spend? Are we talking 100%, taking into consideration that the 1st transaction doesn't get confirmed in the meantime and that the fees are much higher?

Would the same procedure work with additional "fake" transactions or does it somehow lower the success rate? if someone were to invalidate 3, 5, 10... transactions trying to trick several people at once. 

 

[o_e_l_e_o]

I always thought that an RBF transaction can only spend the same UTXO with higher fees to the same address as the original transaction, not a new one like in OPs case.

You can read the requirements for an RBF transaction on the BIP125 proposal which nc50lc linked on the previous page - https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki

In summary, the main requirements are that the initial transaction is opted in to RBF, the replacement transaction pays a higher fee than the one it is replacing, and the replacement transaction spends one or more of the same inputs. There is no stipulation made about spending all the same inputs or sending coins to the same addresses as the first transaction. Theoretically, a transaction could take 20 different inputs and send them to 20 different addresses, and could be replaced by a transaction sending just one of those inputs back to the same address it came from.

If you also see my post on the previous page here, there is a type of RBF called "First Seen Safe" which essentially does as you are describing, but it is not used.

Are we talking 100%, taking into consideration that the 1st transaction doesn't get confirmed in the meantime and that the fees are much higher?

Nothing is ever 100%, and there are some nodes out there which reject all RBF transactions. However, if the first transaction isn't confirmed and is opted in, and the second transaction meets the requirements as above, then there is a high likelihood the first will be replaced.