function randomString(len) {
len = len || 32;
var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefhijklmnoprstuvwxyz1234567890";
var maxPos = chars.length;
var pwd = '';
for (i = 0; i < len; i++) {
pwd += chars.charAt(Math.floor(Math.random() * maxPos));
}
return pwd;
}