Add Async method for converting to seed.

index.js

@@ -1,6 +1,8 @@
 var Buffer = require('safe-buffer').Buffer
 var createHash = require('create-hash')
-var pbkdf2 = require('pbkdf2').pbkdf2Sync
+var _pbkdf2 = require('pbkdf2')
+var pbkdf2 = _pbkdf2.pbkdf2Sync
+var pbkdf2Async = _pbkdf2.pbkdf2
 var randomBytes = require('randombytes')
 
 // use unorm until String.prototype.normalize gets better browser support
@@ -58,6 +60,27 @@ function mnemonicToSeedHex (mnemonic, password) {
   return mnemonicToSeed(mnemonic, password).toString('hex')
 }
 
+function mnemonicToSeedAsync (mnemonic, password) {
+  return new Promise(function (resolve, reject) {
+    try {
+      var mnemonicBuffer = Buffer.from(unorm.nfkd(mnemonic), 'utf8')
+      var saltBuffer = Buffer.from(salt(unorm.nfkd(password)), 'utf8')
+    } catch (error) {
+      return reject(error)
+    }
+
+    pbkdf2Async(mnemonicBuffer, saltBuffer, 2048, 64, 'sha512', function (err, data) {
+      if (err) return reject(err)
+      else return resolve(data)
+    })
+  })
+}
+
+function mnemonicToSeedHexAsync (mnemonic, password) {
+  return mnemonicToSeedAsync(mnemonic, password)
+    .then(function (buf) { return buf.toString('hex') })
+}
+
 function mnemonicToEntropy (mnemonic, wordlist) {
   wordlist = wordlist || DEFAULT_WORDLIST
 
@@ -132,7 +155,9 @@ function validateMnemonic (mnemonic, wordlist) {
 
 module.exports = {
   mnemonicToSeed: mnemonicToSeed,
+  mnemonicToSeedAsync: mnemonicToSeedAsync,
   mnemonicToSeedHex: mnemonicToSeedHex,
+  mnemonicToSeedHexAsync: mnemonicToSeedHexAsync,
   mnemonicToEntropy: mnemonicToEntropy,
   entropyToMnemonic: entropyToMnemonic,
   generateMnemonic: generateMnemonic,

test/index.js

@@ -16,10 +16,13 @@ function testVector (description, wordlist, password, v, i) {
   var vseedHex = v[2]
 
   test('for ' + description + '(' + i + '), ' + ventropy, function (t) {
-    t.plan(5)
+    t.plan(6)
 
     t.equal(bip39.mnemonicToEntropy(vmnemonic, wordlist), ventropy, 'mnemonicToEntropy returns ' + ventropy.slice(0, 40) + '...')
     t.equal(bip39.mnemonicToSeedHex(vmnemonic, password), vseedHex, 'mnemonicToSeedHex returns ' + vseedHex.slice(0, 40) + '...')
+    bip39.mnemonicToSeedHexAsync(vmnemonic, password).then(function (asyncSeedHex) {
+      t.equal(asyncSeedHex, vseedHex, 'mnemonicToSeedHexAsync returns ' + vseedHex.slice(0, 40) + '...')
+    })
     t.equal(bip39.entropyToMnemonic(ventropy, wordlist), vmnemonic, 'entropyToMnemonic returns ' + vmnemonic.slice(0, 40) + '...')
 
     function rng () { return Buffer.from(ventropy, 'hex') }