ERC-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>.

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 EIP-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

Version 0x00

0x19 <0x00> <intended validator address> <data to sign>

The version 0x00 has <intended validator address> for the version specific data. In the case of a Multisig wallet that perform an execution based on a passed signature, the validator address is the address of the Multisig itself. The data to sign could be any arbitrary data.

Version 0x01

The version 0x01 is for structured data as defined in EIP-712

Version 0x45 (E)

0x19 <0x45 (E)> <thereum Signed Message:\n" + len(message)> <data to sign>

The version 0x45 (E) has <thereum Signed Message:\n" + len(message)> for the version-specific data. The data to sign can be any arbitrary data.

NB: The E in Ethereum Signed Message refers to the version byte 0x45. The character E is 0x45 in hexadecimal which makes the remainder, thereum Signed Message:\n + len(message), the version-specific data.

Example

The following snippets has been written in Solidity 0.8.0.

Version 0x00

function signatureBasedExecution(address target, uint256 nonce, bytes memory payload, uint8 v, bytes32 r, bytes32 s) public payable {
        
    // Arguments when calculating hash to validate
    // 1: byte(0x19) - the initial 0x19 byte
    // 2: byte(0) - the version byte
    // 3: address(this) - the validator address
    // 4-6 : Application specific data

    bytes32 hash = keccak256(abi.encodePacked(byte(0x19), byte(0), address(this), msg.value, nonce, payload));

    // recovering the signer from the hash and the signature
    addressRecovered = ecrecover(hash, v, r, s);
   
    // logic of the wallet
    // if (addressRecovered == owner) executeOnTarget(target, payload);
}

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Martin Holst Swende (@holiman), Nick Johnson <arachnid@notdot.net>, "ERC-191: Signed Data Standard," Ethereum Improvement Proposals, no. 191, January 2016. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-191.