Explain the Concept of ‘Double-Spending’ and How Signatures Prevent It

Double-spending is the act of successfully spending the same unit of digital currency more than once. This is a critical problem in digital cash because it can be easily copied.

ECDSA signatures are necessary for authorization, but they alone do not prevent double-spending. The prevention is achieved by the decentralized ledger (blockchain) and the consensus mechanism.

The network validates the ECDSA signature and then checks the ledger to ensure the funds have not already been spent, rejecting any transaction that attempts to spend the same output twice.