Move the 'signing key' code for BAR into common-hash

www/common/common-hash.js

@@ -28,6 +28,13 @@ var factory = function (Util, Crypto, Keys, Nacl) {
         };
     };
 
+    Hash.getSignPublicFromPrivate = function (edPrivateSafeStr) {
+        var edPrivateStr = Crypto.b64AddSlashes(edPrivateSafeStr);
+        var privateKey = Nacl.util.decodeBase64(edPrivateStr);
+        var keyPair = Nacl.sign.keyPair.fromSecretKey(privateKey);
+        return Nacl.util.encodeBase64(keyPair.publicKey);
+    };
+
     var getEditHashFromKeys = Hash.getEditHashFromKeys = function (secret) {
         var version = secret.version;
         var data = secret.keys;

www/common/sframe-common-outer.js

@@ -384,10 +384,7 @@ define([
 
             // This is a burn after reading URL: make sure our owner key is still valid
             try {
-                var nacl = window.nacl;
-                var key = nacl.util.decodeBase64(Crypto.b64AddSlashes(burnAfterReading));
-                var kp = nacl.sign.keyPair.fromSecretKey(key);
-                var publicKey = nacl.util.encodeBase64(kp.publicKey);
+                var publicKey = Utils.Hash.getSignPublicFromPrivate(burnAfterReading);
                 Cryptpad.getPadMetadata({
                     channel: secret.channel
                 }, waitFor(function (md) {