var keyStr = "ABCDEFGHIJKLMNOP" +
             "QRSTUVWXYZabcdef" +
             "ghijklmnopqrstuv" +
             "wxyz0123456789+/" +
             "=";

function encode64(input) {
  var output = "";
  var chr1, chr2, chr3 = "";
  var enc1, enc2, enc3, enc4 = "";
  var i = 0;

  do {
     chr1 = input.charCodeAt(i++);
     chr2 = input.charCodeAt(i++);
     chr3 = input.charCodeAt(i++);

     enc1 = chr1 >> 2;
     enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
     enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
     enc4 = chr3 & 63;

     if (isNaN(chr2)) {
        enc3 = enc4 = 64;
     } else if (isNaN(chr3)) {
        enc4 = 64;
     }

     output = output +
        keyStr.charAt(enc1) +
        keyStr.charAt(enc2) +
        keyStr.charAt(enc3) +
        keyStr.charAt(enc4);
     chr1 = chr2 = chr3 = "";
     enc1 = enc2 = enc3 = enc4 = "";
  } while (i < input.length);

  return output;
}

function decode64(input) {
  var output = "";
  var chr1, chr2, chr3 = "";
  var enc1, enc2, enc3, enc4 = "";
  var i = 0;

  // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
  var base64test = /[^A-Za-z0-9\+\/\=]/g;
  if (base64test.exec(input)) {
     alert("There were invalid base64 characters in the input text.\n" +
           "Valid base64 characters are A-Z, a-z, 0-9, .+., ./., and .=.\n" +
           "Expect errors in decoding.");
  }
  input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

  do {
     enc1 = keyStr.indexOf(input.charAt(i++));
     enc2 = keyStr.indexOf(input.charAt(i++));
     enc3 = keyStr.indexOf(input.charAt(i++));
     enc4 = keyStr.indexOf(input.charAt(i++));

     chr1 = (enc1 << 2) | (enc2 >> 4);
     chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
     chr3 = ((enc3 & 3) << 6) | enc4;

     output = output + String.fromCharCode(chr1);

     if (enc3 != 64) {
        output = output + String.fromCharCode(chr2);
     }
     if (enc4 != 64) {
        output = output + String.fromCharCode(chr3);
     }

     chr1 = chr2 = chr3 = "";
     enc1 = enc2 = enc3 = enc4 = "";

  } while (i < input.length);

  return output;
}