diff --git a/lib/errors/spec.js b/lib/errors/spec.js
index b1d2a7c..0f8545f 100644
--- a/lib/errors/spec.js
+++ b/lib/errors/spec.js
@@ -19,6 +19,9 @@ module.exports = [{
   }, {
     name: 'InvalidState',
     message: format('Invalid state: {0}')
+  }, {
+    name: 'NotImplemented',
+    message: format('Function {0} was not implemented yet')
   }, {
     name: 'InvalidNetworkArgument',
     message: format('Invalid network: must be "livenet" or "testnet", got {0}')
diff --git a/lib/publickey.js b/lib/publickey.js
index 76c854f..d399ef9 100644
--- a/lib/publickey.js
+++ b/lib/publickey.js
@@ -33,6 +33,10 @@ var PublicKey = function PublicKey(data, compressed) {
   if (!data) {
     throw new TypeError('First argument is required, please include public key data.');
   }
+  if (data instanceof PublicKey) {
+    // Return copy, but as it's an immutable object, return same argument
+    return data;
+  }
 
   var info = {
     compressed: typeof(compressed) !== 'undefined' ? compressed : true
@@ -42,7 +46,7 @@ var PublicKey = function PublicKey(data, compressed) {
   if (data instanceof Point) {
     info.point = data;
   } else if (typeof(data) === 'string'){
-    info = PublicKey._transformDER(new Buffer(data, 'hex' ));
+    info = PublicKey._transformDER(new Buffer(data, 'hex'));
   } else if (data instanceof Buffer || data instanceof Uint8Array){
     info = PublicKey._transformDER(data);
   } else if (data.constructor && (data.constructor.name &&
diff --git a/lib/script.js b/lib/script.js
index 7fbdbeb..529444b 100644
--- a/lib/script.js
+++ b/lib/script.js
@@ -5,10 +5,9 @@ var Address = require('./address');
 var BufferReader = require('./encoding/bufferreader');
 var BufferWriter = require('./encoding/bufferwriter');
 var Hash = require('./crypto/hash');
-var Hash = require('./crypto/hash');
 var Opcode = require('./opcode');
 var PublicKey = require('./publickey');
-var PublicKey = require('./publickey');
+var Signature = require('./crypto/signature');
 
 var _ = require('lodash');
 var buffer = require('buffer');
@@ -545,18 +544,17 @@ Script.buildScriptHashOut = function(script) {
  * Builds a scriptSig (a script for an input) that signs a public key hash
  * output script.
  *
- * @param {Object} signature
- * @param {PublicKey} signature.publicKey
- * @param {Buffer} signature.signature
- * @param {number} signature.sigtype
+ * @param {Buffer|string|PublicKey} publicKey
+ * @param {Buffer} signature - the signature in DER cannonical encoding
+ * @param {number=1} sigtype - the type of the signature (defaults to SIGHASH_ALL)
  */
-Script.buildPublicKeyHashIn = function(signature) {
+Script.buildPublicKeyHashIn = function(publicKey, signature, sigtype) {
   var script = new Script()
     .add(bufferUtil.concat([
-      signature.signature.toDER(),
-      bufferUtil.integerAsSingleByteBuffer(signature.sigtype)
+      signature,
+      bufferUtil.integerAsSingleByteBuffer(sigtype || Signature.SIGHASH_ALL)
     ]))
-    .add(signature.publicKey.toBuffer());
+    .add(new PublicKey(publicKey).toBuffer());
   return script;
 };
 
diff --git a/lib/transaction/transaction.js b/lib/transaction/transaction.js
index c0ddbaa..9593479 100644
--- a/lib/transaction/transaction.js
+++ b/lib/transaction/transaction.js
@@ -12,6 +12,8 @@ var Hash = require('../crypto/hash');
 var Sighash = require('./sighash');
 var Signature = require('../crypto/signature');
 
+var errors = require('../errors');
+
 var Address = require('../address');
 var Unit = require('../unit');
 var Input = require('./input');
@@ -176,6 +178,7 @@ Transaction.prototype.from = function(utxo, pubkeys, threshold) {
 };
 
 Transaction.prototype._fromMultiSigP2SH = function(utxo, pubkeys, threshold) {
+  throw new errors.NotImplemented('Transaction#_fromMultiSigP2SH');
 };
 
 Transaction.prototype._fromNonP2SH = function(utxo) {
@@ -275,6 +278,7 @@ Transaction.prototype.to = function() {
 };
 
 Transaction.prototype._payToMultisig = function(pubkeys, threshold, amount) {
+  throw new errors.NotImplemented('Transaction#_payToMultisig');
 };
 
 Transaction.prototype._payToAddress = function(address, amount) {
@@ -344,7 +348,13 @@ Transaction.prototype._getPrivateKeySignatures = function(privKey) {
 };
 
 Transaction.prototype.applySignature = function(signature) {
-  this.inputs[signature.inputIndex].setScript(Script.buildPublicKeyHashIn(signature));
+  this.inputs[signature.inputIndex].setScript(
+    Script.buildPublicKeyHashIn(
+      signature.publicKey,
+      signature.signature.toDER(),
+      signature.sigtype
+    )
+  );
   return this;
 };
 
diff --git a/test/publickey.js b/test/publickey.js
index 497550d..5184ddd 100644
--- a/test/publickey.js
+++ b/test/publickey.js
@@ -43,6 +43,19 @@ describe('PublicKey', function() {
     pk.toString().should.equal(pubhex);
   });
 
+  it('should instantiate from a compressed public key', function() {
+    var publicKeyHex = '031ff0fe0f7b15ffaa85ff9f4744d539139c252a49710fb053bb9f2b933173ff9a';
+    var publicKey = new PublicKey(publicKeyHex);
+    publicKey.toString().should.equal(publicKeyHex);
+  });
+
+  it('should instantiate from another publicKey', function() {
+    var publicKeyHex = '031ff0fe0f7b15ffaa85ff9f4744d539139c252a49710fb053bb9f2b933173ff9a';
+    var publicKey = new PublicKey(publicKeyHex);
+    var publicKey2 = new PublicKey(publicKey);
+    publicKey.should.equal(publicKey2);
+  });
+
   it('should instantiate from a hex encoded DER string', function() {
     var pk = new PublicKey('041ff0fe0f7b15ffaa85ff9f4744d539139c252a49710fb053bb9f2b933173ff9a7baad41d04514751e6851f5304fd243751703bed21b914f6be218c0fa354a341');
     should.exist(pk.point);