//Decrypt message using OpenPGP.js
function decrypt_message(privkey, passphrase, encoded_message) {
           jQuery("#keyerror").addClass("hide");
   var openpgp = window.openpgp;
   var privKeys = openpgp.key.readArmored(privkey);
   var privKey = privKeys.keys[0];
   if(!privKey) {
           jQuery("#keyerror").removeClass("hide");
           jQuery("#keyerror").html("Error: your private key is wrong.");
           return "";
   }
   var success = privKey.decrypt(passphrase);
   if(!success) {
           jQuery("#keyerror").removeClass("hide");
           jQuery("#keyerror").html("Error: your passphrase is wrong.");
           return "";
   }
   var message = openpgp.message.readArmored(encoded_message);
   var decrypted = openpgp.decryptMessage(privKey, message);
   return decrypted;
}