function decode64(input) {
    
 var output = "";
 var chr1, chr2, chr3 = "";
 var enc1, enc2, enc3, enc4 = "";
 var i = 0;
 var keyStr = "ABCDEFGHIJKLMNOP" +
 "QRSTUVWXYZabcdef" +
 "ghijklmnopqrstuv" +
 "wxyz0123456789+/" +
 "=";

 // 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 unescape(output);
 }