bip39.ts

// Copyright 2017-2023 @polkadot/util-crypto authors & contributors
// SPDX-License-Identifier: Apache-2.0

// Adapted from the bitcoinjs/bip39 source
// https://github.com/bitcoinjs/bip39/blob/1d063b6a6aee4145b34d701037cd3e67f5446ff9/ts_src/index.ts
// Copyright (c) 2014, Wei Lu <luwei.here@gmail.com> and Daniel Cousens <email@dcousens.com>
// ISC Licence
//
// Change made in this version -
//   - Adjust formatting (just eslint differences)
//   - Only English wordlist (this aligns with the wasm-crypto implementation)
//   - Use util-crypto randomAsU8a (instead of randombytes)
//   - Remove setting of wordlist passing of wordlist in functions
//   - Remove mnemonicToSeed (we only use the sync variant)
//   - generateMnemonic takes number of words (instead of strength)

import { stringToU8a, u8aToU8a } from '@polkadot/util';

import { pbkdf2Encode } from '../pbkdf2/index.js';
import { randomAsU8a } from '../random/index.js';
import { sha256AsU8a } from '../sha/index.js';
import DEFAULT_WORDLIST from './bip39-en.js';

const INVALID_MNEMONIC = 'Invalid mnemonic';
const INVALID_ENTROPY = 'Invalid entropy';
const INVALID_CHECKSUM = 'Invalid mnemonic checksum';

function normalize (str?: string): string {
  return (str || '').normalize('NFKD');
}

function binaryToByte (bin: string): number {
  return parseInt(bin, 2);
}

function bytesToBinary (bytes: number[]): string {
  return bytes.map((x) => x.toString(2).padStart(8, '0')).join('');
}

function deriveChecksumBits (entropyBuffer: Uint8Array): string {
  return bytesToBinary(
    Array.from(sha256AsU8a(entropyBuffer))
  ).slice(0, (entropyBuffer.length * 8) / 32);
}

export function mnemonicToSeedSync (mnemonic: string, password?: string): Uint8Array {
  return pbkdf2Encode(
    stringToU8a(normalize(mnemonic)),
    stringToU8a(`mnemonic${normalize(password)}`)
  ).password;
}

export function mnemonicToEntropy (mnemonic: string): Uint8Array {
  const words = normalize(mnemonic).split(' ');

  if (words.length % 3 !== 0) {
    throw new Error(INVALID_MNEMONIC);
  }

  // convert word indices to 11 bit binary strings
  const bits = words
    .map((word): string => {
      const index = DEFAULT_WORDLIST.indexOf(word);

      if (index === -1) {
        throw new Error(INVALID_MNEMONIC);
      }

      return index.toString(2).padStart(11, '0');
    })
    .join('');

  // split the binary string into ENT/CS
  const dividerIndex = Math.floor(bits.length / 33) * 32;
  const entropyBits = bits.slice(0, dividerIndex);
  const checksumBits = bits.slice(dividerIndex);

  // calculate the checksum and compare
  const matched = entropyBits.match(/(.{1,8})/g);
  const entropyBytes = matched && matched.map(binaryToByte);

  if (!entropyBytes || (entropyBytes.length % 4 !== 0) || (entropyBytes.length < 16) || (entropyBytes.length > 32)) {
    throw new Error(INVALID_ENTROPY);
  }

  const entropy = u8aToU8a(entropyBytes);

  if (deriveChecksumBits(entropy) !== checksumBits) {
    throw new Error(INVALID_CHECKSUM);
  }

  return entropy;
}

export function entropyToMnemonic (entropy: Uint8Array): string {
  // 128 <= ENT <= 256
  if ((entropy.length % 4 !== 0) || (entropy.length < 16) || (entropy.length > 32)) {
    throw new Error(INVALID_ENTROPY);
  }

  const matched = `${bytesToBinary(Array.from(entropy))}${deriveChecksumBits(entropy)}`.match(/(.{1,11})/g);
  const mapped = matched && matched.map((binary) => DEFAULT_WORDLIST[binaryToByte(binary)]);

  if (!mapped || (mapped.length < 12)) {
    throw new Error('Unable to map entropy to mnemonic');
  }

  return mapped.join(' ');
}

export function generateMnemonic (numWords: 12 | 15 | 18 | 21 | 24): string {
  return entropyToMnemonic(randomAsU8a((numWords / 3) * 4));
}

export function validateMnemonic (mnemonic: string): boolean {
  try {
    mnemonicToEntropy(mnemonic);
  } catch {
    return false;
  }

  return true;
}