What is Double Spend Attack?

A double spend attack refers to a malicious activity involving cryptocurrency. In a double spend attack, a user is able to spend the same amount of cryptocurrency more than once.

Double-spending is a rare phenomenon in the crypto world. In some cases, two or more transactions on a blockchain use the same input. While it is possible to duplicate the digital record of cryptocurrency tokens due to the lack of centralized technology, most cryptocurrencies employ a consensus algorithm to prevent double-spending.

Cryptocurrencies using the Proof-of-Work (PoW) consensus mechanism, such as Bitcoin (BTC), are at higher risk. Experienced programmers with a good understanding of blockchain technology may be able to alter or duplicate digital information.

Since Bitcoin transactions are completed peer-to-peer (P2P), without any intermediaries, it is easier to target them for double-spending attacks. The hackers make a copy of the original transaction to make it look legitimate and original. They can then use the tokens in a different transaction while the initial coins remain in their wallet. In some instances, the first transaction is erased from the blockchain.

Double spend attacks can also be committed by reversing transactions after the assets or services of the counterparty have been received. The hacker then keeps both the assets they received and the assets that the other party was supposed to receive.

In order to hide the transactions or make them appear as if they never took place, hackers can send a number of data units known as packets to the network. This makes it seem like there was no initial transaction.

There are several different types of double spend attacks, such as 51%, Finney, and Race, among others.

51% Attack

A 51% attack, or a majority attack, presents a hypothetical strike against a blockchain network. The idea is that at least 51% of the network nodes are hit, which would grant hackers control of the majority of the network in a consensus mechanism-based system.

51% attacks are extremely complicated to commit as decentralized networks consistently grow larger and the number of network nodes increases.

Finney Attack

A Finney attack can be deceptive, as the merchant does not wait to receive a confirmation of the transaction. A malicious miner can send tokens between wallets. However, the block with this data is not instantly verified.

The user can utilize the tokens in the source wallet to make a purchase. Once the second transaction has been set in place, the miner broadcasts the block that was mined with the information of the first transaction.

Race Attack

A race attack occurs when attackers set up two contradictory transactions and the merchants accept the payments before the transaction is confirmed on the block. The network receives a competing transaction which causes an equal amount of cryptocurrency to return to the attacker. This causes the first transaction to be invalidated.

While double-spending cannot be completely prevented by the blockchain, the network can defend against it as the decentralized validator nodes work on the transaction authentication process.