Foundations of Blockchain

Avoiding the attack

The best way to avoid double-spends on a 51% attack is by increasing the wait time. The longer the wait, the smaller the chances of double-spends. As time passes, the transaction will get buried in the blockchain, making it difficult to reverse the transaction. This can be made sure by waiting for a specific number of block insertions (confirmations) after the transaction is included in a block. Each blockchain platform has its own suggested number of confirmations. The suggested Bitcoin block confirmation is 6, which means a wait time of around 60 minutes after the transaction is included in a block.