diff --git a/lib/hdkey.js b/lib/hdkey.js
index caf60b1..cc3e5ca 100644
--- a/lib/hdkey.js
+++ b/lib/hdkey.js
@@ -54,69 +54,13 @@ Object.defineProperty(HDKey.prototype, 'publicKey', {
 
 Object.defineProperty(HDKey.prototype, 'privateOld', {
   get: function() {
-    // Version
-    var version = VERSIONS.private
-    var buffer = new Buffer(LEN)
-
-    // 4 bytes: version bytes
-    buffer.writeUInt32BE(version, 0)
-
-    // Depth
-    // 1 byte: depth: 0x00 for master nodes, 0x01 for level-1 descendants, ....
-    buffer.writeUInt8(this.depth, 4)
-
-    // 4 bytes: the fingerprint of the parent's key (0x00000000 if master key)
-    var fingerprint = this.depth ? this.parentFingerprint : 0x00000000
-    buffer.writeUInt32BE(fingerprint, 5)
-
-    // 4 bytes: child number. This is the number i in xi = xpar/i, with xi the key being serialized.
-    // This is encoded in Big endian. (0x00000000 if master key)
-    buffer.writeUInt32BE(this.index, 9)
-
-    // 32 bytes: the chain code
-    this.chainCode.copy(buffer, 13)
-
-    // 33 bytes: the public key or private key data
-    assert(this.privateKey, 'Missing private key')
-
-    // 0x00 + k for private keys
-    buffer.writeUInt8(0, 45)
-    this.privateKey.copy(buffer, 46)
-
-
-    return buffer
+    return serialize(this, this.versions.private, Buffer.concat([new Buffer([0]), this.privateKey]))
   }
 })
 
 Object.defineProperty(HDKey.prototype, 'publicOld', {
   get: function() {
-    // Version
-    var version = VERSIONS.public
-    var buffer = new Buffer(LEN)
-
-    // 4 bytes: version bytes
-    buffer.writeUInt32BE(version, 0)
-
-    // Depth
-    // 1 byte: depth: 0x00 for master nodes, 0x01 for level-1 descendants, ....
-    buffer.writeUInt8(this.depth, 4)
-
-    // 4 bytes: the fingerprint of the parent's key (0x00000000 if master key)
-    var fingerprint = this.depth ? this.parentFingerprint : 0x00000000
-    buffer.writeUInt32BE(fingerprint, 5)
-
-    // 4 bytes: child number. This is the number i in xi = xpar/i, with xi the key being serialized.
-    // This is encoded in Big endian. (0x00000000 if master key)
-    buffer.writeUInt32BE(this.index, 9)
-
-    // 32 bytes: the chain code
-    this.chainCode.copy(buffer, 13)
-
-    // X9.62 encoding for public keys
-    var buf = this.publicKey
-    buf.copy(buffer, 45)
-    
-    return buffer
+    return serialize(this, this.versions.public, this.publicKey)
   }
 })
 
@@ -243,9 +187,30 @@ HDKey.fromMasterSeed = function(seedBuffer, versions) {
   return hdkey
 }
 
-//temporary
-function setPrivPub(hd, privKey) {
-  hd.priv = privKey
+function serialize(hdkey, version, key) {
+    var buffer = new Buffer(LEN)
+
+    // 4 bytes: version bytes
+    buffer.writeUInt32BE(version, 0)
+
+    // Depth
+    // 1 byte: depth: 0x00 for master nodes, 0x01 for level-1 descendants, ....
+    buffer.writeUInt8(hdkey.depth, 4)
+
+    // 4 bytes: the fingerprint of the parent's key (0x00000000 if master key)
+    var fingerprint = hdkey.depth ? hdkey.parentFingerprint : 0x00000000
+    buffer.writeUInt32BE(fingerprint, 5)
+
+    // 4 bytes: child number. This is the number i in xi = xpar/i, with xi the key being serialized.
+    // This is encoded in Big endian. (0x00000000 if master key)
+    buffer.writeUInt32BE(hdkey.index, 9)
+
+    // 32 bytes: the chain code
+    hdkey.chainCode.copy(buffer, 13)
 
+    // 0x00 + k for private keys
+    key.copy(buffer, 45)
+
+    return buffer
 }