1 var salt = 'secret key' 

     2 

     3 function mk_hash(s) {

     4     return crypto.createHash('sha1').update(s).digest('hex')

     5 }

     6 

     7 function mk_cookie(c) {

     8     return c.toString() + '-' + mk_hash(c.toString() + salt)

     9 }

    10 

    11 function gt_cookie(s) {

    12     var splits = s.split("-", 2);

    13     var counter = parseInt(splits[0])

    14     var hash = splits[1]

    15     if (mk_hash(counter.toString() + salt) == hash) {

    16         return counter

    17     } else { return 0 }

    18 }

    19 

    20 app.get('/', function(req, res){ .... });