What is a double spend and how does Bitcoin Cash solve it?

A double spend is the payment for a good or service using the same currency twice.

In the fiat money world, a double spend is when a digital transaction, such as a transfer, credit card, payment apps, etc., is reversed and the money returned.

In Bitcoin Cash terms, this would be using the same UTXO (‘unspent transaction output’) more than once to make a payment.

Since, according to Bitcoin Cash consensus rules, if there are two conflicting transactions only one can be accepted as valid, attempting to double spend is a way of defrauding or harming the legitimate recipient of those coins.

Bitcoin Cash Solutions

Currently, the ability for a user to successfully double spend is extremely low and unlikely. There are multiple mitigations implemented on the blockchain and nodes so that this does not occur.

First, consensus rules prohibit the existence of two conflicting, i.e., contradictory, transactions. This means that there cannot be a transaction is spending a coin (also called output) that has been spent in a previous transaction.

On the other hand, in the 2021 Bitcoin Cash update, DS Proofs were incorporated, which allow cryptographically detecting and proving a double spending attempt by a user before the transactions are included in a block.