Topic: double spend transcation (Read 754 times)

One wallet creator could, in theory, write a wallet that didn't allowed you to export your private keys AND didn't allowed you to use the same inputs as the inputs used for an already broadcasted but unconfirmed transaction.
However, the protocol would still allow such double spends to be generated by everybody else.

Also, such a wallet would actually make it very hard (if not impossible) to fix any problems with, 0-fee or to low fee transactions.

I thing one wallet provider  can stop double spending and due to this all service provider have keep atleast 1 conformation before they deliver

There is not much wallet providers can do to stamp out double spending but there is a lot the receiver can do to avoid getting scammed. Wait for at least two confirmations before releasing your goods/service.

I guess it depends on a lot of things...
If you're running a coffee shop, selling a cup of coffee for $2/piece, you might allow 0-conf. If you would only accept FIAT, you might as well run into people leaving without paying (stealing) or using fake money (counterfeiting). It's just the cost of doing business. Sometimes people will try to double spend, just give your security images to the police, file a complaint and never serve the scammer again.

If you sell online subscriptions (like a membership to a streaming service you own), you could also accept 0-conf, since you could just cancell the subscription if the transaction isn't confirmed in 2 hours or something.

If you're selling more expensive, physical objects, i would defenately wait for 1 confirmation before sending the good/letting the client leave. For really expensive stuff (cars, houses,...) i'd even consider waiting 10-15 confirmations, so there's virtually no chance of a fork.

definitely right,and that's why a people are getting recommended to wait atleast 1 confirmation to come and considering it as a transaction that have been completed if the confirmation just arrived rather than risking the money and facing the double spend problem

That is correct. A simplified explanation could be given like this:
- bitcoin is a decentral database, the data in this database is stored in blocks.
- the ammount of bitcoins you own is the sum of the input records stored in the database
- when you send bitcoins to somebody, you create a transaction. This transaction is a piece of text in which you specify which of your input records you'll use to create an output record (this output will be seen as an input record for the receiver's wallet).
- once you've created a transaction, it's broadcasted to the network. At this point, the transaction is unconfirmed (it's not stored in a block, it just resides in the memory of the nodes. It is unconfirmed and can be dropped/forgotten/double spent at any given moment).
- a double spend is when you repeat the process: create a second transaction USING THE SAME inputs.
- the miner now has a choice: he/she either adds the first transaction to a block OR the second transaction. Each input can only be used once, so when he adds the first transaction, the second one will be "cancelled" (and vice versa). The miner usually choses the transaction that has the highest fee.

SOOOOOO.... This can be really usefull when, for example, you created a transaction with a very low (or no) fee, and it's stuck (unconfirmed) for hours (or days). You can create a second transaction, using the same inputs, but with a decent fee... This new transaction can be confirmed much faster, and cancel out the stuck transaction.

Offcourse, the same principle can be applied when buying stuff from a 0-confirmation vendor... Pay him, and before the transaction is added to a block, broadcast a second transaction using the same inputs, but outputs going to YOUR wallet instead of the vendor's... This way, the transaction with output to the vendor will be "cancelled", and the funds are re-routed to your own wallet.... You basically scammed the vendor at this point, since the transaction with outputs to his wallet will never be added to a block, so he wasn't payed.

Once again: this is a simplified explanation... There's a lot more to it, i've actually left out a lot of important stuff in this explanation!!!

ok got your point now ..thanks so in short it can be use for legal purpose or illegal purpose also

Actually, if you pay for goods or services, receive said good or service, double spend the input for the payment transaction to create an output that doesn't go to the vendors wallet, I'm pretty sure its considered stealing in most (if not all) cultures

Double spending in itself is not illegal, but it CAN be used for illegal purposes.

thank you so its not any illegal thing so many can do use this option to be rich .don't you think ??

Actually even some of the online wallet providers disable custom fee feature double spend can't be stopped as there are hardware, desktop wallets from where we can actually use command to send input with custom fee. What these days web wallets have is recommended fee which is very useful for the one who want to get their transaction confirmed within next block or 10 minute.

thank you then there may be many problem in payment if ist low fee and any other can also use same value coin adn sue high value transaction and he can get the fun is that correct or t will just work form the addres it send


yes many one who don't have conformation in there site then it will be bid problem

actually it's not wallet's providers fault,they just enabling the self customization fee to add more flexibility to the wallet users because as you know they want to set the fee whatever the amount they want,but unfortunately this feature is just getting misused by people,so there's born double spend

It's not new, it's not a hacking trick... It's basically how bitcoin works.  It's a rather easy thing to do and it has legitimate uses.

To create a double spend, just create a transaction, broadcast it. Afterwards, generate a new transaction using the same inputs, but with a higher fee, sign the transaction and also broadcast it.
KnightDK even created a java tool to automate the process for you if you want to.

EDIT: https://bitcointalk.org/index.php?topic=1506632.0?

hi i recent found some thing which is quite new to me is double spend transaction ..

any one send fund with quite low fee and this transaction will struck and after some time it will be return toy ur wallet ..

some trick this and sue as for there benefit and use not now but somehow they use more fee and sen that fund to differ account so tey got double benefit ..due to which all gambling company now have 1 confirmation deposit otherwise before the have not confirmation ..

do you know how this is happening ??

and why any wallet  provide si not stopping this hacking trick