AEX 8

AEX: 8
Title: Message Signing
Author: Andreas Gassmann (@AndreasGassmann), Alessandro De Carli (@dcale)
License: BSD-3-Clause
Discussions-To: TBD
Status: Draft
Type: Standards Track
Created: 2019-05-13

Simple Summary

This document defines a standard how arbitrary messages or payload can be signed using an aeternity keypair.

Motivation

Message signing can be used in a wide variety of scenarios. Common use cases include:

• Authentication / Login (Proving you are the owner of an address/pubkey)

• Authorization (Giving a user priviliges based on the coins / tokens he owns)

• Prove Data Integrity

• Voting

This technique has been around for a long time, but with the rise in crypto adoption it becomes more accessible to the average user.

Specification

Flow

1. DApp / Website / Wallet prepares a signing request containing a message (challenge) and other parameters (see below)

2. Signing request is sent to the Wallet / Signer containing the Private Key

3. User can select an identity (= keypair)

4. Message will be signed

5. User is either being redirected to the provided callback URL, or the signed message is displayed (eg. QR code)

Encoding

The signature should be encoded in hex: Buffer.from(signature).toString("hex");

Message Signing Request

const signingRequest = {
	message: string // Message to be signed
	publicKey?: string // OPTIONAL: allows wallet to pre-select signing identity
	ttl?: string // OPTIONAL: Blockheight or timestamp to prevent replay attacks
	origin?: string // OPTIONAL: eg. aeternity.com
	callbackURL?: string // OPTIONAL: eg. https://aeternity.com/?signedMessage=
}

Message Signing Response

const signingResponse = {
	message: string // Message to be signed
	signature: string[] // Signature of the message
	publicKey: string[] // allows wallet to pre-select signing identity
	ttl?: string // Blockheight or timestamp to prevent replay attacks
	origin?: string // OPTIONAL: eg. aeternity.com
}

The response can contain an array of signatures and publicKeys, which allows a single message to be signed by multiple identities at once.

Signing the message

// TODO: How do we fit TTL and hostname into the message?

import * as sodium from "libsodium-wrappers";

const signMessage = async (
  message: string,
  privateKey: Buffer
): Promise<string> => {
  await sodium.ready;
  const signature = sodium.crypto_sign_detached(
    sodium.from_string(message),
    privateKey
  );
  const hexSignature = Buffer.from(signature).toString("hex");

  return hexSignature;
};

Verifying the signature

import * as sodium from "libsodium-wrappers";

const verifyMessage = async (
  message: string,
  hexSignature: string,
  publicKey: Buffer
): Promise<boolean> => {
  await sodium.ready;
  const signature = new Uint8Array(Buffer.from(hexSignature, "hex"));
  const isValidSignature = sodium.crypto_sign_verify_detached(
    signature,
    message,
    publicKey
  );

  return isValidSignature;
};

Example

// risk monitor path sick coconut cube ecology brief table adapt evil oven

const privateKey = Buffer.from(
  "7f192bc4b5d6e828b6aeed3958f791f2d4d0f69e9b34a164df41f0f325c48ceb7d29631b2cc36eb4931a2ebe8b0a1bd95a29825ec21430b9e472146c851d2cfd",
  "hex"
);
const publicKey = Buffer.from(
  "7d29631b2cc36eb4931a2ebe8b0a1bd95a29825ec21430b9e472146c851d2cfd",
  "hex"
);
const message = "This message will be signed.";

const signature = await signMessage(message, publicKey);
// e650110d48b42cf07f577b886f852b36945da4b175cb1629528b705799d1565799802c7fbb7d07685f8b22185db7ce5bd03f7e0e754b904b80b4fe4fda4f1802

const isValidSignature = await verifyMessage(message, signature, publicKey);
// true

Serialization and Transport Layer

Serialization and Transport Layer are not part of this propaosal.

The Serialization is being discussed as part of AEX-7 Data Serialization

Security

In order to prevent malicious DApps from sending a seeminly random message to be signed that actually contains data like a valid transaction, we should add a prefix to the message so this can't be exploited.

https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign