async.until(
        function() {return found},
        function(callback) {
            var hash_array = []
            var possible = 'qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM'
            for (var i = 0; i <= hash_length - 1; i++) {
                var n = (Math.floor(Math.random() * possible.length))
                hash_array.push(possible.charAt(n))
            }

            hash = hash_array.join('')

            cache.get(hash, function(err, res) {

                if (res == false) {
                    found = true
                }
                callback()
            })
        },
        function() {
            cb(hash)
        }
    )