gistfile1.py

import hashlib
import base64
import hmac
import time
    
def _decrypt_cookie(name, value, cookie_secret, include_name=True):
    
    def _cookie_signature(*parts):
        hash = hmac.new(cookie_secret,
                        digestmod=hashlib.sha1)
        for part in parts: hash.update(part)
        return hash.hexdigest()

    def _time_independent_equals(a, b):
        if len(a) != len(b):
            return False
        result = 0
        for x, y in zip(a, b):
            result |= ord(x) ^ ord(y)
            return result == 0
    parts = value.split("|")
    if len(parts) != 3: 
        return None
    if include_name:
        signature = _cookie_signature(name, parts[0], parts[1])
    else:
        signature = _cookie_signature(parts[0], parts[1])
    if not _time_independent_equals(parts[2], signature):
        return None
    timestamp = int(parts[1])
    if timestamp < time.time() - 31 * 86400:
        return None
    if timestamp > time.time() + 31 * 86400:
        return None
    try:
        return base64.b64decode(parts[0])
    except:
        return None