implement entropyToMnemonic

index.js

@@ -13,6 +13,21 @@ BIP39.prototype.mnemonicToSeed = function(mnemonic, password){
   return Crypto.PBKDF2(mnemonic, salt(password), options).toString(Crypto.enc.Hex)
 }
 
+BIP39.prototype.entropyToMnemonic = function(entropy){
+  var entropyBytes = hexToBytes(entropy)
+  var bits = bytesToBinary(entropyBytes)
+
+  var hash = Crypto.SHA256(bytesToWordArray(entropyBytes))
+  var checksumBits = bytesToBinary(wordsToBytes(hash.words))
+  var checksum = checksumBits.substr(0, bits.length / 32)
+
+  var chunks = (bits + checksum).match(/(.{1,11})/g)
+  return chunks.map(function(binary){
+    var index = parseInt(binary, 2)
+    return this.wordlist[index]
+  }, this).join(' ')
+}
+
 function salt(password) {
   return encode_utf8('mnemonic' + (password || ''))
 }
@@ -20,3 +35,43 @@ function salt(password) {
 function encode_utf8(s){
   return unescape(encodeURIComponent(s))
 }
+
+//=========== helper methods from bitcoinjs-lib ========
+
+function hexToBytes(hex) {
+  return hex.match(/../g).map(function(x) {
+    return parseInt(x,16)
+  });
+}
+
+function bytesToBinary(bytes) {
+  return bytes.map(function(x) {
+    return lpad(x.toString(2), '0', 8)
+  }).join('');
+}
+
+function bytesToWordArray(bytes) {
+  return new Crypto.lib.WordArray.init(bytesToWords(bytes), bytes.length)
+}
+
+function bytesToWords(bytes) {
+    var words = [];
+    for (var i = 0, b = 0; i < bytes.length; i++, b += 8) {
+        words[b >>> 5] |= bytes[i] << (24 - b % 32);
+    }
+    return words;
+}
+
+function wordsToBytes(words) {
+    var bytes = [];
+    for (var b = 0; b < words.length * 32; b += 8) {
+        bytes.push((words[b >>> 5] >>> (24 - b % 32)) & 0xFF);
+    }
+    return bytes;
+}
+
+function lpad(str, padString, length) {
+  while (str.length < length) str = padString + str;
+  return str;
+}
+

test/index.js

@@ -3,9 +3,10 @@ var BIP39 = require('../index.js')
 var wordlist = require('../Wordlists/en.json')
 var assert = require('assert')
 
+var bip39 = new BIP39()
+
 describe('constructor', function(){
   it('defaults language to english', function(){
-    var bip39 = new BIP39()
     assert.deepEqual(bip39.wordlist, wordlist)
   })
 })
@@ -13,8 +14,15 @@ describe('constructor', function(){
 describe('mnemonicToSeed', function(){
   vectors.forEach(function(v, i){
     it('works for tests vector ' + i, function(){
-      var bip39 = new BIP39()
       assert.equal(bip39.mnemonicToSeed(v[1], 'TREZOR'), v[2])
     })
   })
 })
+
+describe('entropyToMnemonic', function(){
+  vectors.forEach(function(v, i){
+    it('works for tests vector ' + i, function(){
+      assert.equal(bip39.entropyToMnemonic(v[0]), v[1])
+    })
+  })
+})