---
eip: 155
title: Simple replay attack protection
author: Vitalik Buterin (@vbuterin)
type: Standards Track
category: Core
status: Final
created: 2016-10-14
---

### Hard fork
[Spurious Dragon](./eip-607.md)

### Parameters
- `FORK_BLKNUM`: 2,675,000
- `CHAIN_ID`: 1 (main net)

### Specification

If `block.number >= FORK_BLKNUM` and `CHAIN_ID` is available, then when computing the hash of a transaction for the purposes of signing, instead of hashing only six rlp encoded elements `(nonce, gasprice, startgas, to, value, data)`, you **SHOULD** hash nine rlp encoded elements `(nonce, gasprice, startgas, to, value, data, chainid, 0, 0)`.  If you do, then the `v` of the signature **MUST** be set to `{0,1} + CHAIN_ID * 2 + 35` where `{0,1}` is the parity of the `y` value of the curve point for which `r` is the x-value in the secp256k1 signing process.  If you choose to only hash 6 values, then `v` continues to be set to `{0,1} + 27` as previously.

If `block.number >= FORK_BLKNUM` and `v = CHAIN_ID * 2 + 35` or `v = CHAIN_ID * 2 + 36`, then when computing the hash of a transaction for purposes of recovering, instead of hashing six rlp encoded elements `(nonce, gasprice, startgas, to, value, data)`, hash nine rlp encoded elements `(nonce, gasprice, startgas, to, value, data, chainid, 0, 0)`. The currently existing signature scheme using `v = 27` and `v = 28` remains valid and continues to operate under the same rules as it did previously.

### Example

Consider a transaction with `nonce = 9`, `gasprice = 20 * 10**9`, `startgas = 21000`, `to = 0x3535353535353535353535353535353535353535`, `value = 10**18`, `data=''` (empty).

The "signing data" becomes:

```
0xec098504a817c800825208943535353535353535353535353535353535353535880de0b6b3a764000080018080
```

The "signing hash" becomes:

```
0xdaf5a779ae972f972197303d7b574746c7ef83eadac0f2791ad23db92e4c8e53
```

If the transaction is signed with the private key `0x4646464646464646464646464646464646464646464646464646464646464646`, then the v,r,s values become:

```
(37, 18515461264373351373200002665853028612451056578545711640558177340181847433846, 46948507304638947509940763649030358759909902576025900602547168820602576006531)
```

Notice the use of 37 instead of 27. The signed tx would become:

```
0xf86c098504a817c800825208943535353535353535353535353535353535353535880de0b6b3a76400008025a028ef61340bd939bc2195fe537567866003e1a15d3c71ff63e1590620aa636276a067cbe9d8997f761aecb703304b3800ccf555c9f3dc64214b297fb1966a3b6d83
```

### Rationale

This would provide a way to send transactions that work on Ethereum without working on ETC or the Morden testnet. ETC is encouraged to adopt this EIP but replacing `CHAIN_ID` with a different value, and all future testnets, consortium chains and alt-etherea are encouraged to adopt this EIP replacing `CHAIN_ID` with a unique value.


### List of Chain ID's:

| `CHAIN_ID`     | Chain(s)                                   |
| ---------------| -------------------------------------------|
| 1              | Ethereum mainnet                           |
| 2              | Morden (disused), Expanse mainnet          |
| 3              | Ropsten                                    |
| 4              | Rinkeby                                    |
| 5              | Goerli                                     |
| 42             | Kovan                                      |
| 1337           | Geth private chains (default)              |


Find more chain ID's on [chainid.network](https://chainid.network) and contribute to [ethereum-lists/chains](https://github.com/ethereum-lists/chains).