EIP-155

EIP-155 is a standard implemented on the Ethereum network designed to prevent replay attacks. A replay attack occurs when a valid transaction from one blockchain is maliciously intercepted and broadcasted onto another chain, such as a testnet or a hard fork, where it is also valid.

EIP-155 introduces a chain ID into the transaction signing process. By including this unique identifier in the data signed by the sender, the transaction becomes cryptographically bound to a specific network.

If a user sends a transaction on the mainnet, the signature includes the mainnet chain ID, making it invalid for execution on any other network. This simple addition significantly enhances the security of cross-chain interactions and protects user assets from being unintentionally duplicated or drained.

It serves as a fundamental mechanism for maintaining the integrity of transaction state across fragmented blockchain environments.