README.md

Shamir BIP39

Applies Shamir's Secret Sharing Scheme to BIP39 mnemonics.

Proposed specification: ethereum/EIPs#3450

Installation

Yarn:

yarn add shamir-bip39

NPM:

npm install --save shamir-bip39

API

Split Mnemonic

Split a BIP39 mnemonic into the specified number of shares such that the threshold number of shares are required to recover the original. Each share is a BIP39 mnemonic and an id. Both the mnemonic and the id are required to recover the original mnemonic.

Accepts a BIP39 mnemonic and returns a Shares map, in which the keys are the share id's and the values are the BIP39 mnemonics.

import { splitMnemonic } from 'shamir-bip39';

const mnemonic =
  'jelly better achieve collect unaware mountain thought cargo oxygen act hood bridge';

// Generate 3 shares and require 2 to recover the mnemonic
const shares = splitMnemonic(mnemonic, 3, 2);

// `splitMnemonic` will generate different shares on every run.
// One example result:
{
  '1':
    'liquid use shine dentist aspect brief neither learn hope tourist tray cinnamon',
  '2':
    'liberty antique mean describe wrestle man latin right gown shield decide dynamic',
  '3':
    'install video evil clutch butter asset answer toss noodle captain rate jacket',
};

Recover Mnemonic

Given a Shares object, returns the recovered BIP39 mnemonic.

Note: If the number of shares provided does not meet the threshold, recoverMnemonic will still return a valid BIP39 mnemonic. It just won't be the same as the initial one stored. The user is responsible for providing the minimum number of shares.

import { recoverMnemonic } from 'shamir-bip39';

const shares = {
  '1':
    'liquid use shine dentist aspect brief neither learn hope tourist tray cinnamon',
  '3':
    'install video evil clutch butter asset answer toss noodle captain rate jacket',
};

const originalMnemonic = recoverMnemonic(shares);

expect(originalMnemonic)).toBe(
  'jelly better achieve collect unaware mountain thought cargo oxygen act hood bridge'
);

Acknowledgements

Heavily borrowed from grempe's secrets.js for the implementation of Shamir's and the finite field arithmetic.

With additional inspiration from

• jwerle's sharirs-secret-sharing
• ilap's slip-39-js
• iancoleman's shamir39