diff --git a/aes.js b/aes.js
index ff0d208..508d512 100644
--- a/aes.js
+++ b/aes.js
@@ -91,13 +91,18 @@
 	     */
 	    var AES = C_algo.AES = BlockCipher.extend({
 	        _doReset: function () {
+	            // Skip reset of nRounds has been set before and key did not change
+	            if (this._nRounds && this._keyPriorReset === this._key) {
+	                return;
+	            }
+
 	            // Shortcuts
-	            var key = this._key;
+	            var key = this._keyPriorReset = this._key;
 	            var keyWords = key.words;
 	            var keySize = key.sigBytes / 4;
 
 	            // Compute number of rounds
-	            var nRounds = this._nRounds = keySize + 6
+	            var nRounds = this._nRounds = keySize + 6;
 
 	            // Compute number of key schedule rows
 	            var ksRows = (nRounds + 1) * 4;
diff --git a/bower.json b/bower.json
index 040a841..2d5d339 100644
--- a/bower.json
+++ b/bower.json
@@ -1,6 +1,6 @@
 {
   "name": "crypto-js",
-  "version": "3.1.7",
+  "version": "3.1.8",
   "description": "JavaScript library of crypto standards.",
   "license": "MIT",
   "homepage": "http://github.com/brix/crypto-js",
diff --git a/core.js b/core.js
index afff428..28e34c1 100644
--- a/core.js
+++ b/core.js
@@ -17,6 +17,25 @@
 	 * CryptoJS core components.
 	 */
 	var CryptoJS = CryptoJS || (function (Math, undefined) {
+	    /*
+	     * Local polyfil of Object.create
+	     */
+	    var create = Object.create || (function () {
+	        function F() {};
+
+	        return function (obj) {
+	            var subtype;
+
+	            F.prototype = obj;
+
+	            subtype = new F();
+
+	            F.prototype = null;
+
+	            return subtype;
+	        };
+	    }())
+
 	    /**
 	     * CryptoJS namespace.
 	     */
@@ -31,7 +50,7 @@
 	     * Base object for prototypal inheritance.
 	     */
 	    var Base = C_lib.Base = (function () {
-	        function F() {}
+
 
 	        return {
 	            /**
@@ -54,8 +73,7 @@
 	             */
 	            extend: function (overrides) {
 	                // Spawn
-	                F.prototype = this;
-	                var subtype = new F();
+	                var subtype = create(this);
 
 	                // Augment
 	                if (overrides) {
diff --git a/crypto-js.js b/crypto-js.js
index 7d42a14..3b6c221 100644
--- a/crypto-js.js
+++ b/crypto-js.js
@@ -17,6 +17,25 @@
 	 * CryptoJS core components.
 	 */
 	var CryptoJS = CryptoJS || (function (Math, undefined) {
+	    /*
+	     * Local polyfil of Object.create
+	     */
+	    var create = Object.create || (function () {
+	        function F() {};
+
+	        return function (obj) {
+	            var subtype;
+
+	            F.prototype = obj;
+
+	            subtype = new F();
+
+	            F.prototype = null;
+
+	            return subtype;
+	        };
+	    }())
+
 	    /**
 	     * CryptoJS namespace.
 	     */
@@ -31,7 +50,7 @@
 	     * Base object for prototypal inheritance.
 	     */
 	    var Base = C_lib.Base = (function () {
-	        function F() {}
+
 
 	        return {
 	            /**
@@ -54,8 +73,7 @@
 	             */
 	            extend: function (overrides) {
 	                // Spawn
-	                F.prototype = this;
-	                var subtype = new F();
+	                var subtype = create(this);
 
 	                // Augment
 	                if (overrides) {
@@ -812,34 +830,45 @@
 	            // Shortcuts
 	            var base64StrLength = base64Str.length;
 	            var map = this._map;
+	            var reverseMap = this._reverseMap;
+
+	            if (!reverseMap) {
+	                    reverseMap = this._reverseMap = [];
+	                    for (var j = 0; j < map.length; j++) {
+	                        reverseMap[map.charCodeAt(j)] = j;
+	                    }
+	            }
 
 	            // Ignore padding
 	            var paddingChar = map.charAt(64);
 	            if (paddingChar) {
 	                var paddingIndex = base64Str.indexOf(paddingChar);
-	                if (paddingIndex != -1) {
+	                if (paddingIndex !== -1) {
 	                    base64StrLength = paddingIndex;
 	                }
 	            }
 
 	            // Convert
-	            var words = [];
-	            var nBytes = 0;
-	            for (var i = 0; i < base64StrLength; i++) {
-	                if (i % 4) {
-	                    var bits1 = map.indexOf(base64Str.charAt(i - 1)) << ((i % 4) * 2);
-	                    var bits2 = map.indexOf(base64Str.charAt(i)) >>> (6 - (i % 4) * 2);
-	                    var bitsCombined = bits1 | bits2;
-	                    words[nBytes >>> 2] |= (bitsCombined) << (24 - (nBytes % 4) * 8);
-	                    nBytes++;
-	                }
-	            }
+	            return parseLoop(base64Str, base64StrLength, reverseMap);
 
-	            return WordArray.create(words, nBytes);
 	        },
 
 	        _map: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
 	    };
+
+	    function parseLoop(base64Str, base64StrLength, reverseMap) {
+	      var words = [];
+	      var nBytes = 0;
+	      for (var i = 0; i < base64StrLength; i++) {
+	          if (i % 4) {
+	              var bits1 = reverseMap[base64Str.charCodeAt(i - 1)] << ((i % 4) * 2);
+	              var bits2 = reverseMap[base64Str.charCodeAt(i)] >>> (6 - (i % 4) * 2);
+	              words[nBytes >>> 2] |= (bits1 | bits2) << (24 - (nBytes % 4) * 8);
+	              nBytes++;
+	          }
+	      }
+	      return WordArray.create(words, nBytes);
+	    }
 	}());
 
 
@@ -4429,13 +4458,18 @@
 	     */
 	    var AES = C_algo.AES = BlockCipher.extend({
 	        _doReset: function () {
+	            // Skip reset of nRounds has been set before and key did not change
+	            if (this._nRounds && this._keyPriorReset === this._key) {
+	                return;
+	            }
+
 	            // Shortcuts
-	            var key = this._key;
+	            var key = this._keyPriorReset = this._key;
 	            var keyWords = key.words;
 	            var keySize = key.sigBytes / 4;
 
 	            // Compute number of rounds
-	            var nRounds = this._nRounds = keySize + 6
+	            var nRounds = this._nRounds = keySize + 6;
 
 	            // Compute number of key schedule rows
 	            var ksRows = (nRounds + 1) * 4;
diff --git a/enc-base64.js b/enc-base64.js
index e16a3cb..d5d4082 100644
--- a/enc-base64.js
+++ b/enc-base64.js
@@ -88,34 +88,45 @@
 	            // Shortcuts
 	            var base64StrLength = base64Str.length;
 	            var map = this._map;
+	            var reverseMap = this._reverseMap;
+
+	            if (!reverseMap) {
+	                    reverseMap = this._reverseMap = [];
+	                    for (var j = 0; j < map.length; j++) {
+	                        reverseMap[map.charCodeAt(j)] = j;
+	                    }
+	            }
 
 	            // Ignore padding
 	            var paddingChar = map.charAt(64);
 	            if (paddingChar) {
 	                var paddingIndex = base64Str.indexOf(paddingChar);
-	                if (paddingIndex != -1) {
+	                if (paddingIndex !== -1) {
 	                    base64StrLength = paddingIndex;
 	                }
 	            }
 
 	            // Convert
-	            var words = [];
-	            var nBytes = 0;
-	            for (var i = 0; i < base64StrLength; i++) {
-	                if (i % 4) {
-	                    var bits1 = map.indexOf(base64Str.charAt(i - 1)) << ((i % 4) * 2);
-	                    var bits2 = map.indexOf(base64Str.charAt(i)) >>> (6 - (i % 4) * 2);
-	                    var bitsCombined = bits1 | bits2;
-	                    words[nBytes >>> 2] |= (bitsCombined) << (24 - (nBytes % 4) * 8);
-	                    nBytes++;
-	                }
-	            }
+	            return parseLoop(base64Str, base64StrLength, reverseMap);
 
-	            return WordArray.create(words, nBytes);
 	        },
 
 	        _map: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
 	    };
+
+	    function parseLoop(base64Str, base64StrLength, reverseMap) {
+	      var words = [];
+	      var nBytes = 0;
+	      for (var i = 0; i < base64StrLength; i++) {
+	          if (i % 4) {
+	              var bits1 = reverseMap[base64Str.charCodeAt(i - 1)] << ((i % 4) * 2);
+	              var bits2 = reverseMap[base64Str.charCodeAt(i)] >>> (6 - (i % 4) * 2);
+	              words[nBytes >>> 2] |= (bits1 | bits2) << (24 - (nBytes % 4) * 8);
+	              nBytes++;
+	          }
+	      }
+	      return WordArray.create(words, nBytes);
+	    }
 	}());
 
 
diff --git a/package.json b/package.json
index 0687181..50f9de9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "crypto-js",
-  "version": "3.1.7",
+  "version": "3.1.8",
   "description": "JavaScript library of crypto standards.",
   "license": "MIT",
   "author": {