diff --git a/lib/PayPro.js b/lib/PayPro.js
index f827cf6..1a1623e 100644
--- a/lib/PayPro.js
+++ b/lib/PayPro.js
@@ -1,6 +1,7 @@
 'use strict';
 var imports = require('soop').imports();
 var protobufjs = protobufjs || require('protobufjs/dist/ProtoBuf');
+var Message = Message || require('./Message');
 
 // BIP 70 - payment protocol
 function PayPro() {
@@ -8,8 +9,6 @@ function PayPro() {
   this.message = null;
 }
 
-PayPro.constants = {};
-
 PayPro.PAYMENT_REQUEST_MAX_SIZE = 50000;
 PayPro.PAYMENT_MAX_SIZE = 50000;
 PayPro.PAYMENT_ACK_MAX_SIZE = 60000;
@@ -149,11 +148,19 @@ PayPro.prototype.set = function(key, val) {
 PayPro.prototype.get = function(key) {
   var v = this.message.get(key);
 
+  if (v === null)
+    return v;
+
   //protobuf supports longs, javascript naturally does not
   //convert longs (see long.js, e.g. require('long')) to Numbers
   if (typeof v.low !== 'undefined' && typeof v.high !== 'undefined')
     return v.toInt();
 
+  if (typeof v.toBuffer !== 'undefined') {
+    var maybebuf = v.toBuffer();
+    return Buffer.isBuffer(maybebuf) ? maybebuf : new Buffer(new Uint8Array(maybebuf));
+  }
+
   return v;
 };
 
@@ -171,8 +178,10 @@ PayPro.prototype.serializeForSig = function() {
   if (this.messageType !== 'PaymentRequest')
     throw new Error('serializeForSig is only for PaymentRequest');
 
+  var save = this.message.get('signature');
   this.message.set('signature', new Buffer([]));
   var buf = this.serialize();
+  this.message.set('signature', save);
   return buf;
 };
 
@@ -192,4 +201,46 @@ PayPro.prototype.deserialize = function(buf, messageType) {
   return this;
 };
 
+PayPro.prototype.sign = function(key) {
+  if (this.messageType !== 'PaymentRequest')
+    throw new Error('Signing can only be performed on a PaymentRequest');
+
+  var pki_type = this.get('pki_type');
+
+  if (pki_type === 'SIN')
+    var sig = this.sinSign(key);
+  else
+    throw new Error('Unsupported pki_type');
+  
+  this.set('signature', sig);
+  return this;
+};
+
+PayPro.prototype.verify = function() {
+  if (this.messageType !== 'PaymentRequest')
+    throw new Error('Verifying can only be performed on a PaymentRequest');
+
+  var pki_type = this.get('pki_type');
+
+  if (pki_type === 'SIN')
+    return this.sinVerify();
+  else
+    throw new Error('Unsupported pki_type');
+};
+
+//default signing function for prototype.sign
+PayPro.prototype.sinSign = function(key) {
+  this.set('pki_data', key.public)
+  var buf = this.serializeForSig();
+  return Message.sign(buf, key);
+};
+
+//default verify function
+PayPro.prototype.sinVerify = function() {
+  var sig = this.get('signature');
+  var pubkey = this.get('pki_data');
+  var buf = this.serializeForSig();
+  return Message.verifyWithPubKey(pubkey, buf, sig);
+};
+
 module.exports = require('soop')(PayPro);
diff --git a/test/test.PayPro.js b/test/test.PayPro.js
index ab1b710..d8dcf31 100644
--- a/test/test.PayPro.js
+++ b/test/test.PayPro.js
@@ -240,4 +240,83 @@ describe('PayPro', function() {
 
   });
 
+  describe('#sign', function() {
+
+    it('should sign a payment request', function() {
+      var pd = new PayPro.PaymentDetails();
+      pd.set('time', 0);
+      var pdbuf = pd.toBuffer();
+      var paypro = new PayPro();
+      paypro.makePaymentRequest();
+      paypro.set('serialized_payment_details', pdbuf);
+      paypro.set('pki_type', 'SIN');
+      var key = new bitcore.Key();
+      key.private = bitcore.util.sha256('test key');
+      key.regenerateSync();
+      paypro.sign(key);
+      var sig = paypro.get('signature');
+      sig.length.should.be.greaterThan(0);
+    });
+
+  });
+
+  describe('#verify', function() {
+
+    it('should verify a signed payment request', function() {
+      var pd = new PayPro.PaymentDetails();
+      pd.set('time', 0);
+      var pdbuf = pd.toBuffer();
+      var paypro = new PayPro();
+      paypro.makePaymentRequest();
+      paypro.set('serialized_payment_details', pdbuf);
+      paypro.set('pki_type', 'SIN');
+      var key = new bitcore.Key();
+      key.private = bitcore.util.sha256('test key');
+      key.regenerateSync();
+      paypro.sign(key);
+      var verify = paypro.verify();
+      verify.should.equal(true);
+    });
+
+  });
+
+  describe('#sinSign', function() {
+
+    it('should sign assuming pki_type is SIN', function() {
+      var pd = new PayPro.PaymentDetails();
+      pd.set('time', 0);
+      var pdbuf = pd.toBuffer();
+      var paypro = new PayPro();
+      paypro.makePaymentRequest();
+      paypro.set('serialized_payment_details', pdbuf);
+      paypro.set('pki_type', 'SIN');
+      var key = new bitcore.Key();
+      key.private = bitcore.util.sha256('test key');
+      key.regenerateSync();
+      var sig = paypro.sinSign(key);
+      sig.length.should.be.greaterThan(0);
+    });
+
+  });
+
+  describe('#sinVerify', function() {
+
+    it('should verify assuming pki_type is SIN', function() {
+      var pd = new PayPro.PaymentDetails();
+      pd.set('time', 0);
+      var pdbuf = pd.toBuffer();
+      var paypro = new PayPro();
+      paypro.makePaymentRequest();
+      paypro.set('serialized_payment_details', pdbuf);
+      paypro.set('pki_type', 'SIN');
+      var key = new bitcore.Key();
+      key.private = bitcore.util.sha256('test key');
+      key.regenerateSync();
+      paypro.sign(key);
+      var verify = paypro.sinVerify();
+      verify.should.equal(true);
+    });
+
+  });
+
 });