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Replay Attack Meaning

A replay attack is a security vulnerability that can occur during a "Hard Fork," where a blockchain splits into two separate networks. If a user sends a transaction on the first chain, an attacker could record that transaction and "Replay" it on the second chain.

If the user held coins on both chains, the attacker could effectively steal their funds on the second chain without their consent.The attack is possible because both chains share the same transaction history and use the same private keys up until the moment of the fork. To prevent this, developers implement Unique Chain IDs.

If a transaction is sent on Chain A (ID: 1), it will be rejected by Chain B (ID: 2) because the IDs don't match. This ensures that a transaction is only valid on the specific network the user intended, keeping the two ledgers distinct.For users, the main risk of a replay attack occurs in the days immediately following a contentious fork.

If a new fork doesn't have strong replay protection, it is safer to move your coins to a new address on one chain before interacting with the other. Most modern forks now include this protection by default, but it remains a critical due diligence point for anyone holding assets during a major network split.

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