Decrypt Chrome Linux Blob Encrypted Cookies in Python

Decrypt Chrome Linux BLOB encrypted cookies in Python

I've posted an example Python script here for decoding the encrypted cookies in either OSX or Linux.

Decrypting Chromium cookies

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))

Chrome 80 how to decode cookies

Since Chrome version 80 and higher, cookies are encrypted using AES-256 in GCM mode. The applied key is encrypted using DPAPI. The details are described here, section Chrome v80.0 and higher.

The encrypted key starts with the ASCII encoding of DPAPI (i.e. 0x4450415049) and is Base64 encoded, i.e. the key must first be Base64 decoded and the first 5 bytes must be removed. Afterwards a decryption with win32crypt.CryptUnprotectData is possible. The decryption returns a tuple whose second value contains the decrypted key:

import os
import json
import base64 
import win32crypt
from Crypto.Cipher import AES

path = r'%LocalAppData%\Google\Chrome\User Data\Local State'
path = os.path.expandvars(path)
with open(path, 'r') as file:
    encrypted_key = json.loads(file.read())['os_crypt']['encrypted_key']
encrypted_key = base64.b64decode(encrypted_key)                                       # Base64 decoding
encrypted_key = encrypted_key[5:]                                                     # Remove DPAPI
decrypted_key = win32crypt.CryptUnprotectData(encrypted_key, None, None, None, 0)[1]  # Decrypt key

The encryption of the cookies is performed with AES-256 in GCM mode. This is authenticated encryption, which guarantees confidentiality and authenticity/integrity. During encryption an authentication tag is generated, which is used for integrity verification during decryption. The GCM mode is based on the CTR mode and uses an IV (nonce). In addition to the 32 bytes key, the nonce and the authentication tag are required for decryption.

The encrypted data start with the ASCII encoding of v10 (i.e. 0x763130), followed by the 12 bytes nonce, the actual ciphertext and finally the 16 bytes authentication tag. The individual components can be separated as follows:

data = bytes.fromhex('763130...') # the encrypted cookie
nonce = data[3:3+12]
ciphertext = data[3+12:-16]
tag = data[-16:]

whereby data contains the encrypted data. The decryption itself is done using PyCryptodome with:

cipher = AES.new(decrypted_key, AES.MODE_GCM, nonce=nonce)
plaintext = cipher.decrypt_and_verify(ciphertext, tag) # the decrypted cookie

Note: Generally, there are also cookies stored that have been saved with Chrome versions below v80 and are therefore DPAPI encrypted. DPAPI encrypted cookies can be recognized by the fact that they start with the sequence 0x01000000D08C9DDF0115D1118C7A00C04FC297EB, here and here, section About DPAPI. These cookies can of course not be decrypted as described above, but with the former procedure for DPAPI encrypted cookies. Tools to view cookies in unencrypted or encrypted form are ChromeCookiesView or DB Browser for SQLite, respectively.

Decryption problem when using linux cookies on windows

... when I download it directly and copy-paste it to my profile directory, my chromedriver logs error:

[... ERROR:os_crypt_win.cc(61)] Failed to decrypt: The parameter is incorrect. (0x57)

It looks like it is not possible. Or maybe not possible they way you are trying to do it. It takes extra effort.

The question Decrypting Chrome's cookies on windows has a link to os_crypt_win.cc. os_crypt_win.cc uses DPAPI, which is the old WinCrypt gear. DPAPI ties encryption to a user's Windows login. DPAPI also places a MAC on the encrypted data. I believe the MAC is the reason for the message you are seeing: "The parameter is incorrect". DPAPI sees the MAC over the encrypted data is wrong, and it gives you the generic error message.

So if you truly want to use the Linux cookie on Windows, you will need to decrypt it using the Linux spec, and then re-encrypt it using the Windows spec.

If you are going to pursue it, then you may want to visit this BlackHat talk: Reversing dpapi and stealing windows secrets offline. It will allow you to encrypt the user's data on Linux for Windows.

Encrypted cookies in Chrome

Alright, so in case anyone is interested, I found a solution to this problem after alot of trial, error and googling.

Google Chrome cookies DB has 2 columns for storing values: "value" and "encrypted_value", the latter being used when the cookie stored was requested to be encrypted - often the case with certain confidential information and long-time session keys.

After figuring this out, I then needed to find a way to access this key, stored as a Blob value. I found several guides on how to do this, but the one that ended up paying of was: http://www.codeproject.com/Questions/56109/Reading-BLOB-in-Sqlite-using-C-NET-CF-PPC

Simply reading the value is not enough, as it is encrypted. - Google Chrome uses triple DES encryption with the current users password as seed on windows machines. In order to decrypt this in C#, one should use Windows Data Protection API (DPAPI), there are a few guides out there on how to make use of it.

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