In the context of cryptocurrencies, double-spending is a potential attack where an individual or entity attempts to spend the same cryptocurrency token more than once.
In a traditional financial system, double-spending is prevented by intermediaries such as banks that keep track of account balances and transactions. However, cryptocurrencies are decentralized and lack intermediaries, which makes them vulnerable to double-spending attacks.
The double-spending attack works by a bad actor creating two transactions that spend the same cryptocurrency token, and then broadcasting both transactions to the network simultaneously. The network would then consider both transactions as valid, and the attacker would have successfully spent the same cryptocurrency token twice.
To prevent double-spending attacks, cryptocurrencies use a consensus mechanism such as proof-of-work (PoW) or proof-of-stake (PoS) to validate transactions and ensure that only one version of the transaction is added to the blockchain. Cryptocurrency networks also have a mechanism to detect and reject transactions that attempt to spend the same cryptocurrency token twice.