python - Decrypting Chromium cookies

Question

I'm trying to use Chromium cookies in Python, because Chromium encrypts its cookies using AES (with CBC) I need to reverse this.

I can recover the AES key from OS X's Keychain (it's stored in Base 64):

security find-generic-password -w -a Chrome -s Chrome Safe Storage
# From Python:
python -c 'from subprocess import PIPE, Popen; print(Popen(['security', 'find-generic-password', '-w', '-a', 'Chrome', '-s', 'Chrome Safe Storage'], stdout=PIPE).stdout.read().strip())'

Here's the code I have, all I'm missing is decrypting the cookies:

from subprocess import PIPE, Popen
from sqlite3 import dbapi2

def get_encryption_key():
  cmd = ['security', 'find-generic-password', '-w', '-a', 'Chrome', '-s', 'Chrome Safe Storage']
  return Popen(cmd, stdout=PIPE).stdout.read().strip().decode('base-64')

def get_cookies(database):
  key = get_encryption_key()
  with dbapi2.connect(database) as conn:
    conn.rollback()
    rows = conn.cursor().execute('SELECT name, encrypted_value FROM cookies WHERE host_key like ".example.com"')

  cookies = {}
  for name, enc_val in rows:
    val = decrypt(enc_val, key) # magic missing
    cookies[name] = val

  return cookies

I tried a bunch of things with pyCrypto's AES module but:

1. I have no Initialization Vector (IV)
2. enc_val is not a multiple of 16 in length

Here are some links that seem useful:

• the commit that started it all
• components/encryptor/keychain_password_mac.mm
• AES key generation (not used in OS X but could help someone else)
• cookie insertion function

Can you help me figure this out?

Answer 1

You're on the right track! I've been working on this for a few days and finally figured it out. (Many thanks to the OP for the helpful links to the Chromium source.)

I've put up a post with a little more detail and a working script, but here is the basic idea:

#! /usr/bin/env python3

from Crypto.Cipher import AES
from Crypto.Protocol.KDF import PBKDF2

# Function to get rid of padding
def clean(x): 
    return x[:-x[-1]].decode('utf8')

# replace with your encrypted_value from sqlite3
encrypted_value = ENCRYPTED_VALUE 

# Trim off the 'v10' that Chrome/ium prepends
encrypted_value = encrypted_value[3:]

# Default values used by both Chrome and Chromium in OSX and Linux
salt = b'saltysalt'
iv = b' ' * 16
length = 16

# On Mac, replace MY_PASS with your password from Keychain
# On Linux, replace MY_PASS with 'peanuts'
my_pass = MY_PASS
my_pass = my_pass.encode('utf8')

# 1003 on Mac, 1 on Linux
iterations = 1003

key = PBKDF2(my_pass, salt, length, iterations)
cipher = AES.new(key, AES.MODE_CBC, IV=iv)

decrypted = cipher.decrypt(encrypted_value)
print(clean(decrypted))