Fiesta Exploit Kit String Decrypter

function decrypt(fragment, offset) {
    var key = 'iZ2HN7b_c5re4h3dDf18R96ajO0QP';
    var tmp_result = '';
    var additional_offset = 0;
    for (var i = 0; i < fragment.length; i++) {
        additional_offset += offset;
        var key_index = key.indexOf(fragment.charAt(i));
        key_index = (key_index + additional_offset) % key.length;
        tmp_result += key.charAt(key_index)
    }

    var result = '';
    for (var i = 0; i < tmp_result.length; i += 2) {
        var hexval = tmp_result.substr(i, 2);
        var chrcode = parseInt(hexval, 16);
        result += String.fromCharCode(chrcode);
    }
    return result;
}