cookie.py

from operator import or_ as bit_or
from operator import xor as bit_xor
from itertools import imap
import hmac
from pack.util import codec

class CookieStore(object):
  def __init__(self, secret_key):
    if not secret_key:
      self.secret_key = secure_random_bytes(16)
    elif isinstance(secret_key, str):
      self.secret_key = get_bytes(secret_key)
    else:
      self.secret_key = secret_key
  def read_session(self, data):
    if data:
      return unseal(self.secret_key, data)
    else:
      return {}
  def write_session(self, _, data):
    return seal(self.secret_key, data)
  def delete_session(self, _):
    return seal(self.secret_key, {})

def seal(key, data):
  data = encrypt(key, get_bytes(repr(data)))
  return "%s--%s" % (codec.base64_encode(data), hmac(key, data))

def unseal(key, string):
  "Restore a sealed object from a string."
  data, mac = string.split("--")
  data = codec.base64_decode(data)
  if secure_compare(mac, hmac(key, data)):
    return read_string(decrypt(key, data))

def encrypt(key, data):
  cipher = 

def decrypt(key, data):
  cipher = 

def hmac(key, data):
  return codec.base64_encode(hmac.new(key, data, hashlib.sha256).digest())

def secure_compare(a, b):
  if a and b and len(a) == len(b):
    return 0 == reduce(bit_or,
      imap(bit_xor, get_bytes(a), get_bytes(b)))
  else:
    return False

def secure_random_bytes(size):
  seed = bytearray

def get_bytes(string):
  return [ord(x) for x in string]