diff --git a/lib/saml11.js b/lib/saml11.js
index f359aa54..3651f701 100644
--- a/lib/saml11.js
+++ b/lib/saml11.js
@@ -42,7 +42,7 @@ exports.create = function(options, callback) {
                   algorithms.digest[options.digestAlgorithm]);
 
   sig.signingKey = options.key;
-  
+
   sig.keyInfoProvider = {
     getKeyInfo: function () {
       return "<X509Data><X509Certificate>" + cert + "</X509Certificate></X509Data>";
@@ -66,9 +66,9 @@ exports.create = function(options, callback) {
 
   if (options.lifetimeInSeconds) {
     conditions[0].setAttribute('NotBefore', now.format('YYYY-MM-DDTHH:mm:ss.SSS[Z]'));
-    conditions[0].setAttribute('NotOnOrAfter', now.add(options.lifetimeInSeconds, 'seconds').format('YYYY-MM-DDTHH:mm:ss.SSS[Z]'));
+    conditions[0].setAttribute('NotOnOrAfter', now.clone().add(options.lifetimeInSeconds, 'seconds').format('YYYY-MM-DDTHH:mm:ss.SSS[Z]'));
   }
-  
+
   if (options.audiences) {
     var audiences = options.audiences instanceof Array ? options.audiences : [options.audiences];
     audiences.forEach(function (audience) {
@@ -83,7 +83,7 @@ exports.create = function(options, callback) {
     var statement = doc.documentElement.getElementsByTagNameNS(NAMESPACE, 'AttributeStatement')[0];
     Object.keys(options.attributes).forEach(function(prop) {
       if(typeof options.attributes[prop] === 'undefined') return;
-      
+
       // <saml:Attribute AttributeName="name" AttributeNamespace="http://schemas.xmlsoap.org/claims/identity">
       //    <saml:AttributeValue>Foo Bar</saml:AttributeValue>
       // </saml:Attribute>
@@ -110,15 +110,15 @@ exports.create = function(options, callback) {
     .setAttribute('AuthenticationInstant', now.format('YYYY-MM-DDTHH:mm:ss.SSS[Z]'));
 
   var nameID = doc.documentElement.getElementsByTagNameNS(NAMESPACE, 'NameIdentifier')[0];
-  
+
   if (options.nameIdentifier) {
     nameID.textContent = options.nameIdentifier;
-  
+
     doc.getElementsByTagName('saml:AuthenticationStatement')[0]
       .getElementsByTagName('saml:NameIdentifier')[0]
       .textContent = options.nameIdentifier;
   }
-  
+
   if (options.nameIdentifierFormat) {
     var nameIDs = doc.documentElement.getElementsByTagNameNS(NAMESPACE, 'NameIdentifier');
     nameIDs[0].setAttribute('Format', options.nameIdentifierFormat);
@@ -127,18 +127,18 @@ exports.create = function(options, callback) {
 
   if (!options.encryptionCert) return sign(options, sig, doc, callback);
 
-  // encryption is turned on, 
+  // encryption is turned on,
   var proofSecret;
   async.waterfall([
     function(cb) {
-      if (!options.subjectConfirmationMethod && options.subjectConfirmationMethod !== 'holder-of-key') 
+      if (!options.subjectConfirmationMethod && options.subjectConfirmationMethod !== 'holder-of-key')
         return cb();
-      
+
       crypto.randomBytes(32, function(err, randomBytes) {
         proofSecret = randomBytes;
         addSubjectConfirmation(options, doc, options.holderOfKeyProofSecret || randomBytes, cb);
       });
-      
+
     },
     function(cb) {
       sign(options, sig, doc, function(err, signed) {
@@ -150,7 +150,7 @@ exports.create = function(options, callback) {
     if (err) return callback(err);
     callback(null, result, proofSecret);
   });
-}; 
+};
 
 function addSubjectConfirmation(options, doc, randomBytes, callback) {
   var encryptOptions = {
@@ -159,7 +159,7 @@ function addSubjectConfirmation(options, doc, randomBytes, callback) {
     keyEncryptionAlgorighm: options.keyEncryptionAlgorighm || 'http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p'
   };
 
-  xmlenc.encryptKeyInfo(randomBytes, encryptOptions, function(err, keyinfo) { 
+  xmlenc.encryptKeyInfo(randomBytes, encryptOptions, function(err, keyinfo) {
     if (err) return cb(err);
     var subjectConfirmationNodes = doc.documentElement.getElementsByTagNameNS(NAMESPACE, 'SubjectConfirmation');
 
@@ -185,9 +185,9 @@ function sign(options, sig, doc, callback) {
   var signed;
 
   try {
-    var opts = options.xpathToNodeBeforeSignature ? { 
-      location: { 
-        reference: options.xpathToNodeBeforeSignature, 
+    var opts = options.xpathToNodeBeforeSignature ? {
+      location: {
+        reference: options.xpathToNodeBeforeSignature,
         action: 'after'
       }
     } : {};