EIP-155: Simple replay attack protection
What does EIP-155 do?
EIP-155 adds simple replay attack protection by including the chain ID in transaction signatures. Transactions include the chain identifier (1 for mainnet, etc.) when computing the signing hash, preventing a transaction signed for one network from being replayed on another.
Why is it important?
This was critical after the Ethereum/Ethereum Classic split. Without chain IDs, a transaction sent on one chain could be copied and executed on the other. This standard now protects all Ethereum-compatible chains from cross-chain replay attacks.
Hard fork
Parameters
FORK_BLKNUM: 2,675,000CHAIN_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 and contribute to ethereum-lists/chains.