EIP-1344: Add chain id opcode (#1344)

* Add chain id opcode

* Update EIP number

* Update file name

* Add discussion-to

EIPS/eip-1344.md

@@ -0,0 +1,16 @@
+---
+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.