var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + //all caps

"abcdefghijklmnopqrstuvwxyz" + //all lowercase

"0123456789+/="; // all numbers plus +/=

function base64_decode(inp)

{

var out = ""; //This is the output

var chr1, chr2, chr3 = ""; //These are the 3 decoded bytes

var enc1, enc2, enc3, enc4 = ""; //These are the 4 bytes to be decoded

var i = 0; //Position counter

// remove all characters that are not A-Z, a-z, 0-9, +, /, or =

var base64test = /[^A-Za-z0-9\+\/\=]/g;

if (base64test.exec(inp)) { //Do some error checking

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.");

}

inp = inp.replace(/[^A-Za-z0-9\+\/\=]/g, "");

do { //Here’s the decode loop.

//Grab 4 bytes of encoded content.

enc1 = keyStr.indexOf(inp.charAt(i++));

enc2 = keyStr.indexOf(inp.charAt(i++));

enc3 = keyStr.indexOf(inp.charAt(i++));

enc4 = keyStr.indexOf(inp.charAt(i++));

//Heres the decode part. There’s really only one way to do it.

chr1 = (enc1 << 2) | (enc2 >> 4);

chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);

chr3 = ((enc3 & 3) << 6) | enc4;

//Start to output decoded content

out = out + String.fromCharCode(chr1);

if (enc3 != 64) {

out = out + String.fromCharCode(chr2);

}

if (enc4 != 64) {

out = out + String.fromCharCode(chr3);

}

//now clean out the variables used

chr1 = chr2 = chr3 = "";

enc1 = enc2 = enc3 = enc4 = "";

} while (i < inp.length); //finish off the loop

//Now return the decoded values.

return out;

}