EIP-191: Signed Data Standard

Abstract

This ERC proposes a specification about how to handle signed data in Ethereum contracts.

Motivation

Several multisignature wallet implementations have been created which accepts presigned transactions. A presigned transaction is a chunk of binary signed_data, along with signature (r, s and v). The interpretation of the signed_data has not been specified, leading to several problems:

• Standard Ethereum transactions can be submitted as signed_data. An Ethereum transaction can be unpacked, into the following components: RLP<nonce, gasPrice, startGas, to, value, data> (hereby called RLPdata), r, s and v. If there are no syntactical constraints on signed_data, this means that RLPdata can be used as a syntactically valid presigned transaction.
• Multisignature wallets have also had the problem that a presigned transaction has not been tied to a particular validator, i.e a specific wallet. Example:
  1. Users A, B and C have the 2/3-wallet X
  2. Users A, B and D have the 2/3-wallet Y
  3. User A and B submit presigned transactions to X.
  4. Attacker can now reuse their presigned transactions to X, and submit to Y.

Specification

We propose the following format for signed_data

0x19 <1 byte version> <version specific data> <data to sign>.

Version 0 has <20 byte address> for the version specific data, and the address is the intended validator. In the case of a Multisig wallet, that is the wallet’s own address .

The initial 0x19 byte is intended to ensure that the signed_data is not valid RLP

For a single byte whose value is in the [0x00, 0x7f] range, that byte is its own RLP encoding.

That means that any signed_data cannot be one RLP-structure, but a 1-byte RLP payload followed by something else. Thus, any ERC-191 signed_data can never be an Ethereum transaction.

Additionally, 0x19 has been chosen because since ethereum/go-ethereum#2940 , the following is prepended before hashing in personal_sign:

"\x19Ethereum Signed Message:\n" + len(message).

Using 0x19 thus makes it possible to extend the scheme by defining a version 0x45 (E) to handle these kinds of signatures.

Registry of version bytes

Example

The following snippet has been written in Solidity 0.5.0.

function submitTransactionPreSigned(address destination, uint value, bytes data, uint nonce, uint8 v, bytes32 r, bytes32 s)
    public
    returns (bytes32 transactionHash)
{
    // Arguments when calculating hash to validate
    // 1: byte(0x19) - the initial 0x19 byte
    // 2: byte(0) - the version byte
    // 3: this - the validator address
    // 4-7 : Application specific data
    transactionHash = keccak256(abi.encodePacked(byte(0x19),byte(0),address(this),destination, value, data, nonce));
    sender = ecrecover(transactionHash, v, r, s);
    // ...
}

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Martin Holst Swende, Nick Johnson, "EIP-191: Signed Data Standard," Ethereum Improvement Proposals, no. 191, January 2016. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-191.