Double Spend help

[rajat08]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

[shorena]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

A "double-spend" in bitcoin is typically understood as.

#1 Alice creates one transaction (A1) with a low fee to pay Bob 1 BTC
#2 Bob provides a service to Alice
#3 Alice creates a different transaction (A2) that uses the same coins as A1, but pays a higher fee.
#4 Alice heavily pushes A2 in the hopes that A1 will be forgotten by the network and not confirmed. If A2 gets confirmed A1 is invalid, if A1 gets confirmed A2 is invalid.

There are variations of this, but there are no true double spends possible. No coins can be used twice and get confirmed.

[coinzat]

a double spend can occur when the same input is used in two or more different transactions.

when this happen, on of these transactions only will be confirmed and the others will get nothing. that is why when you deal with someone, you should wait for the first confirmation 

[rajat08]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

A "double-spend" in bitcoin is typically understood as.

#1 Alice creates one transaction (A1) with a low fee to pay Bob 1 BTC
#2 Bob provides a service to Alice
#3 Alice creates a different transaction (A2) that uses the same coins as A1, but pays a higher fee.
#4 Alice heavily pushes A2 in the hopes that A1 will be forgotten by the network and not confirmed. If A2 gets confirmed A1 is invalid, if A1 gets confirmed A2 is invalid.

There are variations of this, but there are no true double spends possible. No coins can be used twice and get confirmed.

So no true double spend is possible. its a theory concept only.

[shorena]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

A "double-spend" in bitcoin is typically understood as.

#1 Alice creates one transaction (A1) with a low fee to pay Bob 1 BTC
#2 Bob provides a service to Alice
#3 Alice creates a different transaction (A2) that uses the same coins as A1, but pays a higher fee.
#4 Alice heavily pushes A2 in the hopes that A1 will be forgotten by the network and not confirmed. If A2 gets confirmed A1 is invalid, if A1 gets confirmed A2 is invalid.

There are variations of this, but there are no true double spends possible. No coins can be used twice and get confirmed.

So no true double spend is possible. its a theory concept only.

It happens because people like Bob accept unconfirmed transactions without defending against the possible attack by alice. Its not easy in most cases so its rare, but its more than a theory concept.

See here -> http://bitcoinist.net/peter-todd-double-spends-on-coinbase/

[rajat08]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

A "double-spend" in bitcoin is typically understood as.

#1 Alice creates one transaction (A1) with a low fee to pay Bob 1 BTC
#2 Bob provides a service to Alice
#3 Alice creates a different transaction (A2) that uses the same coins as A1, but pays a higher fee.
#4 Alice heavily pushes A2 in the hopes that A1 will be forgotten by the network and not confirmed. If A2 gets confirmed A1 is invalid, if A1 gets confirmed A2 is invalid.

There are variations of this, but there are no true double spends possible. No coins can be used twice and get confirmed.

So no true double spend is possible. its a theory concept only.

It happens because people like Bob accept unconfirmed transactions without defending against the possible attack by alice. Its not easy in most cases so its rare, but its more than a theory concept.

See here -> http://bitcoinist.net/peter-todd-double-spends-on-coinbase/

ok got your point and thanks to peter for his honesty.

[VirosaGITS]

ok got your point and thanks to peter for his honesty.

Thats pretty nice, but i didnt really get how he did it, to Coinbase or from Coinbase? Since Coinbase doesnt credit you anything until 6 transaction or something.

Also as a merchant selling coffee, you could simply make it so that you need a mandatory fee higher than the average, so let say, you ask for double the normal transaction fee, let say 8 cents instead of 4 cents. Then you deduct that from the coffee price, so that the price does not raise for the buyer.

Then this is a 1.66% to 2% loss in return. You have to ask yourself if its likely that more than 2% of your sales are going to be double spend. Probably not, so this is minimal, but probably why low cost transaction are not attempted to be secured by sellers.

[btcdevil]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

as per my knowledge and experience i have not seen any type of double spend the balance in wallet, how can a wallet double spend means keeping 1btc in wallet but twice sending to two addresses , i think it is not possible with the genuine wallets, but after seeing some replys i think it can happen.

[shorena]

has any body seen any double spent being detected in there transactions? I haven't seen anywhere.
How can someone double spend there bitcoins??

What happens to transaction that are detected as double spend??

as per my knowledge and experience i have not seen any type of double spend the balance in wallet, how can a wallet double spend means keeping 1btc in wallet but twice sending to two addresses , i think it is not possible with the genuine wallets, but after seeing some replys i think it can happen.

Most wallet would not display it as such. Lets take bitcoin core as an example how to handle something like that very well. If it for some reason sees both transactions it would mark them as "conflicted" so you know there is something wrong while you wait for a confirmation. On the other hand it does not allow you to just issue another transaction with the same coins. You have to remove* all transactions from your wallet, rescan* for all confirmed (!) transactions and afterwards create the TX again. The steps marked with * can not be done via the user interface, but you need to pass specific commands on startup. Its not difficult, but its also not just a simple click of a button.

[Velkro]

Some very well oriented in computer world guys, could double spend with enough time (only while 0 confirmations).
Thats why 0 confirmations is not safe, you should wait for at least 1 confirmation.

[Your Point Is Invalid]

you can find the tool that Todd used to doublespend here
https://github.com/petertodd/replace-by-fee-tools/blob/master/doublespend.py

i think u will need to compile that

[Amph]

it must be said that a double spend done by the infamous 51% did not happen yet

Some very well oriented in computer world guys, could double spend with enough time (only while 0 confirmations).
Thats why 0 confirmations is not safe, you should wait for at least 1 confirmation.

1 is not enough in some case, there are atatck that need 4-5 confirmations and some need even 6, like finney attack

[Snorek]

I just can add that double spending is not customer problem as much as companies which accept bitcoin. If you are just a normal bitcoin user it is not a concern for you.
Coinbase for example appears to be by default obliged to accept 0 confirmation payments, something they apparently struggle to do successfully.