diff --git a/.gitignore b/.gitignore
index c88e5e8..1d13986 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 bower_components
-.idea
\ No newline at end of file
+.idea
+.project
diff --git a/index.html b/index.html
index 3c1689f..1698b80 100644
--- a/index.html
+++ b/index.html
@@ -268,8 +268,7 @@ <h3 class="card-header primary-color white-text">VERIFY OTS PROOF</h3>
 <!-- MDB core JavaScript -->
 <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/mdbootstrap/4.5.0/js/mdb.min.js"></script>
 <!-- OpenTimestamps JavaScript (use the default opentimestamps.org one, or any local version -->
-<script src="https://opentimestamps.org/assets/javascripts/vendor/opentimestamps.min.js"></script>
-<!-- script src="../javascript-opentimestamps/dist/opentimestamps.js"></script -->
+<script src="../assets/javascripts/vendor/opentimestamps.min.js"></script>
 <!-- Moment JavaScript -->
 <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.1/moment.min.js"></script>
 <script src="https://cdnjs.cloudflare.com/ajax/libs/moment-timezone/0.5.17/moment-timezone-with-data-2012-2022.min.js"></script>
diff --git a/index.js b/index.js
index 2ef8159..0c73ea4 100644
--- a/index.js
+++ b/index.js
@@ -1,5 +1,44 @@
+/* OpenTimestamps functions */
+
 const OpenTimestamps = window.OpenTimestamps
 
+// an empty list would be equivalent to the default calendars
+const calendarsList = [
+    'https://test-calendar.aniasafe.it',  // testnet
+    'https://calendar.aniasafe.it',       // mainet
+    'https://alice.btc.calendar.opentimestamps.org', 
+    'https://bob.btc.calendar.opentimestamps.org',
+    'https://finney.calendar.eternitywall.com'
+]
+
+// an empty list is not acceptable here
+const wcalendars = [
+    'https://test-calendar.aniasafe.it',  // testnet
+    'https://calendar.aniasafe.it',       // mainet
+    'https://alice.btc.calendar.opentimestamps.org',
+    'https://bob.btc.calendar.opentimestamps.org',
+    'https://finney.calendar.eternitywall.com'
+]
+const whitelistedCalendars = new OpenTimestamps.Calendar.UrlWhitelist(wcalendars)
+
+const blockexplorers = {
+	bitcoin: {
+	  explorers: [
+    	{url: 'https://blockstream.info/api', type: 'blockstream'},
+    	{url: 'https://blockexplorer.com/api', type: 'insight'}
+      ],
+      timeout: 5
+    },
+    bitcoinTestnet: {
+	  explorers: [
+		{url: 'https://blockstream.info/testnet/api', type: 'blockstream'},
+		{url: 'https://testnet.blockexplorer.com/api', type: 'insight'}
+	  ],
+      timeout: 5
+    }
+}
+
+
 $("#btn-hash").click(function(event) {
     event.preventDefault()
     // begin processing...
@@ -63,11 +102,13 @@ $("#btn-stamp").click(function(event) {
 
     const hashValue = $("#stamp-hashValue").val()
     const hashData = hexToBytes(hashValue)
-    const detachedOriginal = OpenTimestamps.DetachedTimestampFile.fromHash(op, hashData)
 
     const filename = $("#stamp-filename").val()
 
-    OpenTimestamps.stamp(detachedOriginal).then( () => {
+    const detachedOriginal = OpenTimestamps.DetachedTimestampFile.fromHash(op, hashData)
+	const options = { calendars: calendarsList }
+
+    OpenTimestamps.stamp(detachedOriginal, options).then( () => {
         const byteots = detachedOriginal.serializeToBytes()
         const hexots = bytesToHex(byteots)
         $("#stamp-output").val(hexots)
@@ -165,7 +206,8 @@ $("#btn-upgrade").click(function(event) {
     const filename = $("#upgrade-filename").val()
     $("#verify-filename").val(filename)
 
-    OpenTimestamps.upgrade(detachedStamped).then( (changed)=>{
+    const upgradeOptions = { whitelist: whitelistedCalendars }
+    OpenTimestamps.upgrade(detachedStamped, upgradeOptions).then( (changed)=>{
         const timestampBytes = detachedStamped.serializeToBytes()
         const hexots = bytesToHex(timestampBytes)
         if (changed === true) {
@@ -205,7 +247,8 @@ $("#btn-verify").click(function(event) {
     const filename = $("#verify-filename").val()
     var outputText = ""
 
-    OpenTimestamps.upgrade(detachedStamped).then( (changed)=>{
+    const upgradeOptions = { whitelist: whitelistedCalendars }
+    OpenTimestamps.upgrade(detachedStamped, upgradeOptions).then( (changed)=>{
         const timestampBytes = detachedStamped.serializeToBytes()
         hexots = bytesToHex(timestampBytes)
         if (changed === true) {
@@ -225,7 +268,7 @@ $("#btn-verify").click(function(event) {
             outputText += "No proof upgrade available"
         }
         $("#verify-output").val(outputText + "\nWaiting for verification results...")
-        return OpenTimestamps.verifyTimestamp(detachedStamped.timestamp)
+        return OpenTimestamps.verifyTimestamp(detachedStamped.timestamp, blockexplorers)
     }).then( (results)=>{
         if (Object.keys(results).length === 0) {
             if (!detachedStamped.timestamp.isTimestampComplete())