---
eip: 191
title: Signed Data Standard
author: Martin Holst Swende (@holiman), Nick Johnson <arachnid@notdot.net>
status: Draft
type: Standards Track
category: ERC
created: 2016-01-20
---

# 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` submites `presigned` transaction 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](https://github.com/ethereum/wiki/wiki/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

| Version byte | EIP            | Description
| ------------ | -------------- | -----------
|    `0x00`    | [191][eip-191] | Data with intended validator
|    `0x01`    | [712][eip-712] | Structured data
|    `0x45`    | [191][eip-191] | `personal_sign` messages

[eip-191]: https://eips.ethereum.org/EIPS/eip-191
[eip-712]: https://eips.ethereum.org/EIPS/eip-712

### Example

    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(byte(0x19),byte(0),this,destination, value, data, nonce);
        sender = ecrecover(transactionHash, v, r, s);
        // ...
    }

## Copyright

Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).