---
eip: 1344
title: ChainID opcode
author: Richard Meissner (@rmeissner)
discussions-to: https://ethereum-magicians.org/t/add-chain-id-opcode-for-replay-protection-when-handling-signed-messages-in-contracts/1131
category: Core
type: Standards Track
status: Draft
created: 2018-08-22
---
 ### Specification
 Adds a new opcode at 0x46, which takes 0 stack arguments. It will return the chain id of the chain where the block was mined. It should cost 2 gas (G_base) to execute this opcode.
 ### Motivation
 [EIP-155](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-155.md) proposes to use the chain id to prevent replay attacks between different chains. It would be a great benefit to have the same possibility inside smart contracts when handling signatures. 
 The current approach proposed by [EIP-712](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-712.md) is to specify the chain id on compile time. Using this approach will result in problems after a hardfork. 
 By adding the opcode it would be possible to access the current chain id and validate signatures based on that.