metamask-extension/app/scripts/lib/seed-phrase-verifier.js

import KeyringController from 'eth-keyring-controller'
import log from 'loglevel'

const seedPhraseVerifier = {

  /**
   * Verifies if the seed words can restore the accounts.
   *
   * Key notes:
   * - The seed words can recreate the primary keyring and the accounts belonging to it.
   * - The created accounts in the primary keyring are always the same.
   * - The keyring always creates the accounts in the same sequence.
   *
   * @param {array} createdAccounts - The accounts to restore
   * @param {string} seedWords - The seed words to verify
   * @returns {Promise<void>} - Promises undefined
   *
  */
  async verifyAccounts (createdAccounts, seedWords) {
    if (!createdAccounts || createdAccounts.length < 1) {
      throw new Error('No created accounts defined.')
    }

    const keyringController = new KeyringController({})
    const Keyring = keyringController.getKeyringClassForType('HD Key Tree')
    const opts = {
      mnemonic: seedWords,
      numberOfAccounts: createdAccounts.length,
    }

    const keyring = new Keyring(opts)
    const restoredAccounts = await keyring.getAccounts()
    log.debug('Created accounts: ' + JSON.stringify(createdAccounts))
    log.debug('Restored accounts: ' + JSON.stringify(restoredAccounts))

    if (restoredAccounts.length !== createdAccounts.length) {
      // this should not happen...
      throw new Error('Wrong number of accounts')
    }

    for (let i = 0; i < restoredAccounts.length; i++) {
      if (restoredAccounts[i].toLowerCase() !== createdAccounts[i].toLowerCase()) {
        throw new Error('Not identical accounts! Original: ' + createdAccounts[i] + ', Restored: ' + restoredAccounts[i])
      }
    }
  },
}

export default seedPhraseVerifier