hdkey: added toJSON()/fromJSON()

lib/hdkey.js

@@ -158,6 +158,13 @@ HDKey.prototype.deriveChild = function (index) {
   return hd
 }
 
+HDKey.prototype.toJSON = function () {
+  return {
+    privateExtendedKey: this.privateExtendedKey,
+    publicExtendedKey: this.publicExtendedKey
+  }
+}
+
 HDKey.fromMasterSeed = function (seedBuffer, versions) {
   var I = crypto.createHmac('sha512', MASTER_SECRET).update(seedBuffer).digest()
   var IL = I.slice(0, 32)
@@ -197,6 +204,10 @@ HDKey.fromExtendedKey = function (base58key, versions) {
   return hdkey
 }
 
+HDKey.fromJSON = function (obj) {
+  return HDKey.fromExtendedKey(obj.privateExtendedKey)
+}
+
 function serialize (hdkey, version, key) {
   // => version(4) || depth(1) || fingerprint(4) || index(4) || chain(32) || key(33)
   var buffer = new Buffer(LEN)

test/hdkey.test.js

@@ -18,6 +18,24 @@ describe('hdkey', function () {
         assert.equal(childkey.privateExtendedKey, f.private)
         assert.equal(childkey.publicExtendedKey, f.public)
       })
+
+      describe('> ' + f.path + ' toJSON() / fromJSON()', function () {
+        it('should return an object read for JSON serialization', function () {
+          var hdkey = HDKey.fromMasterSeed(new Buffer(f.seed, 'hex'))
+          var childkey = hdkey.derive(f.path)
+
+          var obj = {
+            privateExtendedKey: f.private,
+            publicExtendedKey: f.public
+          }
+
+          assert.deepEqual(childkey.toJSON(), obj)
+
+          var newKey = HDKey.fromJSON(obj)
+          assert.strictEqual(newKey.privateExtendedKey, f.private)
+          assert.strictEqual(newKey.publicExtendedKey, f.public)
+        })
+      })
     })
   })