How to protect yourself from a Finney attack?
The first recommendation is to wait at least 6 confirmations on the Bitcoin network to consider a transaction as safe and irreversible.. Despite the decentralization of the network has grown so much that in the vast majority of cases with 1 or 2 it may even be enough, being able to even value the number of confirmations based on the amount transacted.
For example, if you are going to accept less than € 100, with a confirmation it may be enough because the cost of the attack would be enormously higher. Games theory y el Nash equilibrium it will never favor executing the attack.
As we have mentioned in previous articles on irreversible transactions, Bitcoin transactions will be irreversible as new blocks are generated on which the transaction includes. Reflecting each new block as a confirmation to the included transaction. However, for considerable amounts, it is recommended to wait for 6 confirmations to ensure that the transaction is practically impossible to reverse. For what remains at the risk of a user or merchant, accept unconfirmed transactions by another person.
If an attacker intends to use the Finney attack to obtain some illiquid asset, it is difficult to match the need for this asset with the search for a block. However, if you use it as a way to get something liquid, like exchanging bitcoins for another currency, there is always an opportunity to realize yourself. But it is likely that the merchant asked him for a number of confirmations to carry out the action. So in practice it is quite difficult and improbable to achieve something like this.