diff --git a/js/securityLib/sha256.js b/js/securityLib/sha256.js
index 00ea8af..214ee4d 100644
--- a/js/securityLib/sha256.js
+++ b/js/securityLib/sha256.js
@@ -252,8 +252,10 @@
 {
   //console.log('Raw string comming is '+input);
   var output = Array(input.length >> 2);
+  /* JavaScript automatically zeroizes a new array.
   for(var i = 0; i < output.length; i++)
     output[i] = 0;
+   */
   for(var i = 0; i < input.length * 8; i += 8)
     output[i>>5] |= (input.charCodeAt(i / 8) & 0xFF) << (24 - i % 32);
   return output;
@@ -268,8 +270,10 @@
 function byteArray2binb(input){
 	//console.log("Byte array coming is " + input);
 	var output = Array(input.length >> 2);
+      /* JavaScript automatically zeroizes a new array.
 	  for(var i = 0; i < output.length; i++)
 	    output[i] = 0;
+       */
 	  for(var i = 0; i < input.length * 8; i += 8)
 	    output[i>>5] |= (input[i / 8] & 0xFF) << (24 - i % 32);
 	  return output;
@@ -322,15 +326,25 @@
   var HASH = new Array(1779033703, -1150833019, 1013904242, -1521486534,
                        1359893119, -1694144372, 528734635, 1541459225);
   var W = new Array(64);
-  var a, b, c, d, e, f, g, h;
-  var i, j, T1, T2;
 
   /* append padding */
   m[l >> 5] |= 0x80 << (24 - l % 32);
   m[((l + 64 >> 9) << 4) + 15] = l;
+ 
+  for(var offset = 0; offset < m.length; offset += 16)
+    processBlock_sha256(m, offset, HASH, W);
 
-  for(i = 0; i < m.length; i += 16)
-  {
+  return HASH;
+}
+
+/*
+ * Process a block of 16 4-byte words in m starting at offset and update HASH.  
+ * offset must be a multiple of 16 and less than m.length.  W is a scratchpad Array(64).
+ */
+function processBlock_sha256(m, offset, HASH, W) {
+    var a, b, c, d, e, f, g, h;
+    var j, T1, T2;
+    
     a = HASH[0];
     b = HASH[1];
     c = HASH[2];
@@ -342,7 +356,7 @@
 
     for(j = 0; j < 64; j++)
     {
-      if (j < 16) W[j] = m[j + i];
+      if (j < 16) W[j] = m[j + offset];
       else W[j] = safe_add(safe_add(safe_add(sha256_Gamma1256(W[j - 2]), W[j - 7]),
                                             sha256_Gamma0256(W[j - 15])), W[j - 16]);
 
@@ -367,8 +381,6 @@
     HASH[5] = safe_add(f, HASH[5]);
     HASH[6] = safe_add(g, HASH[6]);
     HASH[7] = safe_add(h, HASH[7]);
-  }
-  return HASH;
 }
 
 function safe_add (x, y)
@@ -377,3 +389,87 @@
   var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
   return (msw << 16) | (lsw & 0xFFFF);
 }
+
+/*
+ * Create a Sha256, call update(data) multiple times, then call finalize().
+ */
+var Sha256 = function Sha256() {
+    this.W = new Array(64);
+    this.hash = new Array(1779033703, -1150833019, 1013904242, -1521486534,
+                          1359893119, -1694144372, 528734635, 1541459225);
+    this.nTotalBytes = 0;
+    this.buffer = new Uint8Array(16 * 4);
+    this.nBufferBytes = 0;
+}
+
+/*
+ * Update the hash with data, which is Uint8Array.
+ */
+Sha256.prototype.update = function(data) {
+    this.nTotalBytes += data.length;
+    
+    if (this.nBufferBytes > 0) {
+        // Fill up the buffer and process it first.
+        var bytesNeeded = this.buffer.length - this.nBufferBytes;
+        if (data.length < bytesNeeded) {
+            this.buffer.set(data, this.nBufferBytes);
+            this.nBufferBytes += data.length;
+            return;
+        }
+        else {
+            this.buffer.set(data.subarray(0, bytesNeeded), this.nBufferBytes);
+            processBlock_sha256(byteArray2binb(this.buffer), 0, this.hash, this.W);
+            this.nBufferBytes = 0;
+            // Consume the bytes from data.
+            data = data.subarray(bytesNeeded, data.length);
+            if (data.length == 0)
+                return;
+        }
+    }
+    
+    // 2^6 is 16 * 4.
+    var nBlocks = data.length >> 6;
+    if (nBlocks > 0) {
+        var nBytes = nBlocks * 16 * 4;
+        var m = byteArray2binb(data.subarray(0, nBytes));
+        for(var offset = 0; offset < m.length; offset += 16)
+            processBlock_sha256(m, offset, this.hash, this.W);
+
+        data = data.subarray(nBytes, data.length);
+    }
+    
+    if (data.length > 0) {
+        // Save the remainder in the buffer.
+        this.buffer.set(data);
+        this.nBufferBytes = data.length;
+    }
+}
+
+/*
+ * Finalize the hash and return the result as Uint8Array.
+ * Only call this once.  Return values on subsequent calls are undefined.
+ */
+Sha256.prototype.finalize = function() {
+    var m = byteArray2binb(this.buffer.subarray(0, this.nBufferBytes));
+    /* append padding */
+    var l = this.nBufferBytes * 8;
+    m[l >> 5] |= 0x80 << (24 - l % 32);
+    m[((l + 64 >> 9) << 4) + 15] = this.nTotalBytes * 8;
+
+    for(var offset = 0; offset < m.length; offset += 16)
+        processBlock_sha256(m, offset, this.hash, this.W);
+
+    return Sha256.binb2Uint8Array(this.hash);
+}
+
+/*
+ * Convert an array of big-endian words to Uint8Array.
+ */
+Sha256.binb2Uint8Array = function(input)
+{
+    var output = new Uint8Array(input.length * 4);
+    var iOutput = 0;
+    for (var i = 0; i < input.length * 32; i += 8)
+        output[iOutput++] = (input[i>>5] >>> (24 - i % 32)) & 0xFF;
+    return output;
+}
diff --git a/js/testing/test-sha256.html b/js/testing/test-sha256.html
index 4020f53..5980dac 100644
--- a/js/testing/test-sha256.html
+++ b/js/testing/test-sha256.html
@@ -11,11 +11,21 @@
 	<script src="http://crypto-js.googlecode.com/svn/tags/3.0.2/build/rollups/sha256.js"></script>
 	
 	<script type="text/javascript">
-		function hash(){			
+		function hash(){		
 			var input = document.getElementById('contentname').value;
 			
 			var output = "from string- " + hex_sha256(input) + "<br/>";
-			output += "from bytes-- " + hex_sha256_from_bytes(DataUtils.toNumbersFromString(input)) + "<br/>";			
+            
+            var sha256 = new Sha256();
+            var data = DataUtils.toNumbersFromString(input);
+            // Call update multiple times in small chunks to test the buffering.
+            var chunkSize = 3;
+            var nCalls = Math.floor(data / chunkSize);
+            for (var i = 0; i < nCalls; ++i)
+                sha256.update(data.subarray(i * chunkSize, chunkSize));
+            sha256.update(data.subarray(i * nCalls, data.length));
+			output += "from bytes-- " + DataUtils.toHex(sha256.finalize()) + "<br/>";			
+            
 			output += "reference---- " + CryptoJS.SHA256(input);
 			
 			document.getElementById('result').innerHTML = output;