Double spending while spending bitcoin on stores

[Lorenzo]

Do you think it's possible and dangerous?

Because it needs around a minute to 2 hours to confirm a block, and there is no way to wait a confirmation while you on the queqe line.
Let just say they're "okay" with no current block confirmation and let you leave the store, but what if someone just sent a payment with no fees, make them not included and confirmed in the next block, Then after he leaves he quickly create a new transaction into his new wallet, make a double spending.

What do you think?

It's so unlikely improvable that it's like worrying that your credit card may or not may have confirmed the payment through your bank. People dont worry about this, they seem to think credit cards are instantaneous.. people should think like that about BTC but its even more secure.

I think someone must have tried double spending to test the network and so far there is no successful double spending attempts. Back to OP's question on buying a coffee with a transaction without a fee. I think merchants can assess the likelihood of it confirming and decide to accept or reject your payment.

A distinction should be made between double spending where the same coins are spent twice and both transactions are confirmed and included in the blockchain and double spending where two transactions are broadcasted at roughly the same time and only one of these transactions actually goes through. The former scenario would only be possible in a 51 percent attack while the latter one is very much possible today.

you can double spend yout bits with some scripting skill.
But unfortunately, updated wallets are not allowing you to double spend

Most wallets don't allow for double spending. As you said - in order to attempt it, you would need to make the transaction using a custom script.

[Meuh6879]

oh, and ... by the way ... the reality of nodes x 6400 

[rikkie]

you can't double spend in an open environment ...
you can double-spend with a isolated bitcoin core server and local network ... and a wallet with "trusted IP" pointed on this server (to accept 0-confirmation transaction).

in real world, you can't have this ... even if you want. 

This is not true.....well unless it is assumed that the attacker does not control any mining hardware and only executes his attack with nodes.

If an attacker were to broadcast a particular transaction that is accepted by the nodes and then confirms a valid block that double spends at least one of the inputs from the transaction then the original transaction will no longer be valid and will fall out of the node's memory pool. Another alternative to confirming the double spend themselves would be to pay a pool to confirm a specific tx that happens to double spend at least one input from the unconfirmed transaction in question, I know there at least used to be at least one pool that offered this "service"

[picolo]

you can't double spend in an open environment ...
you can double-spend with a isolated bitcoin core server and local network ... and a wallet with "trusted IP" pointed on this server (to accept 0-confirmation transaction).

in real world, you can't have this ... even if you want. 

This is not true.....well unless it is assumed that the attacker does not control any mining hardware and only executes his attack with nodes.

If an attacker were to broadcast a particular transaction that is accepted by the nodes and then confirms a valid block that double spends at least one of the inputs from the transaction then the original transaction will no longer be valid and will fall out of the node's memory pool. Another alternative to confirming the double spend themselves would be to pay a pool to confirm a specific tx that happens to double spend at least one input from the unconfirmed transaction in question, I know there at least used to be at least one pool that offered this "service"

It is possible but complicated, costly and the shop will know so you can't shop there anymore without risking getting caught.

[superresistant]

 
Is there such thing as a "well trusted and connected nodes list " ?

I put myself in a situation of a merchant that want to prevent race attack.

[turvarya]

you can't double spend in an open environment ...
you can double-spend with a isolated bitcoin core server and local network ... and a wallet with "trusted IP" pointed on this server (to accept 0-confirmation transaction).

in real world, you can't have this ... even if you want. 

This is not true.....well unless it is assumed that the attacker does not control any mining hardware and only executes his attack with nodes.

If an attacker were to broadcast a particular transaction that is accepted by the nodes and then confirms a valid block that double spends at least one of the inputs from the transaction then the original transaction will no longer be valid and will fall out of the node's memory pool. Another alternative to confirming the double spend themselves would be to pay a pool to confirm a specific tx that happens to double spend at least one input from the unconfirmed transaction in question, I know there at least used to be at least one pool that offered this "service"

The pool would also have to find the next block ...

[Soros Shorts]

Is there such thing as a "well trusted and connected nodes list " ?

I put myself in a situation of a merchant that want to prevent race attack.

The one you quietly build yourself with servers colocated around the globe and with persistent connections to the biggest pools.