Encode in Laravel, decode in Python

Question

I'm using Laravel's encryptString method to encrypt some data on my website. This uses OpenSSL's 256-bit AES-CBC encryption without any serialization. I'm now trying to decrypt that data in Python but I keep getting errors about key length and can't seem to figure out why.

Example data to decrypt: eyJpdiI6ImdxY0VcLzFodmpISFV4allSWmJDdEpRPT0iLCJ2YWx1ZSI6IkxXd0ZJaUd2bTUweW5pNm0wUjQwOFM2N1wvWEs5SlYrNB4xNlR7Qkh1U3FvPSIsIm1hYyI6Ijc5ZWM0YTYxYjljZGFiNzgwNjY2NDU1ZmQ5Yjc1ZmJlOGU4NzBkMjQzMzA3MmVhYzE3NzY4ZmU1MWIyMjZlOTQifQ==

Example Key to use for decryption (from laravel .env):
base64:/AZejP0lh3McL/+Vy5yZcADdTcR65qnx5Jqinuw7raK=

I changed those values around so actually decrypting with those values won't give any real data, just figured it'd be good for example. I then try to decrypt this data in Python 3.7 with:

import base64
from Crypto.Cipher import AES

def decrypt(enc, key):
    IV = 16 * '\x00'
    decobj = AES.new(key, AES.MODE_CBC, IV)
    data = decobj.decrypt(base64.b64decode(enc))
    print(str(data.decode()))

if __name__ == "__main__":
    key = b"/AZejP0lh3McL/+Vy5yZcADdTcR65qnx5Jqinuw7raK="
    decrypt("eyJpdiI6ImdxY0VcLzFodmpISFV4allSWmJDdEpRPT0iLCJ2YWx1ZSI6IkxXd0ZJaUd2bTUweW5pNm0wUjQwOFM2N1wvWEs5SlYrNB4xNlR7Qkh1U3FvPSIsIm1hYyI6Ijc5ZWM0YTYxYjljZGFiNzgwNjY2NDU1ZmQ5Yjc1ZmJlOGU4NzBkMjQzMzA3MmVhYzE3NzY4ZmU1MWIyMjZlOTQifQ==", key)

And it seems like this should work, but when I run it I get the error: ValueError: Incorrect AES key length (60 bytes) so I'm not sure what I'm doing wrong. I've tried padding/unpadding the data/key but that doesn't seem to change anything. I'm wondering if I'm getting the wrong key to use for decryption from Laravel, but from what I could tell in the linked documentation, it should just be the APP_KEY in my .env file.

If anyone could help me or point me in the right direction, that would be amazing!

This question is unique to other similar questions because I'm trying to figure out primarily if I'm getting the correct AES key from Laravel, I don't actually overly need help decrypting, I just think I'm grabbing the wrong key from Laravel.

EDIT: New code that seems like it works:

import base64
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad

def decrypt(enc, key):
    IV = 16 * '\x00'.encode()
    decobj = AES.new(key, AES.MODE_CBC, IV)
    data = decobj.decrypt(pad(base64.b64decode(enc), 16))
    print(base64.b64decode(data))

if __name__ == "__main__":
    key = base64.b64decode(b"/AZejP0lh3McL/+Vy5yZcADdTcR65qnx5Jqinuw7raK=")
    decrypt("eyJpdiI6ImdxY0VcLzFodmpISFV4allSWmJDdEpRPT0iLCJ2YWx1ZSI6IkxXd0ZJaUd2bTUweW5pNm0wUjQwOFM2N1wvWEs5SlYrNB4xNlR7Qkh1U3FvPSIsIm1hYyI6Ijc5ZWM0YTYxYjljZGFiNzgwNjY2NDU1ZmQ5Yjc1ZmJlOGU4NzBkMjQzMzA3MmVhYzE3NzY4ZmU1MWIyMjZlOTQifQ==", key)

The print statement now prints some bytes, but when I run .decode() on it I get the error: UnicodeDecodeError: 'utf-8' codec can't decode byte 0xfa in position 0: invalid start byte and can't seem to figure out what I need to do to make it be able to be printed as a string.

Answer 1

import base64
import json
from Crypto.Cipher import AES
from Crypto.Util.Padding import unpad

encoded_key = '' #Remove the 'base64:' prefix from the APP_KEY value
decoded_key = base64.urlsafe_b64decode(encoded_key.encode()) 

enc_pass = '' #encryption string

p_obj = json.loads(base64.b64decode(enc_pass).decode())
decobj = AES.new(decoded_key, AES.MODE_CBC, base64.b64decode(p_obj['iv']))
data = decobj.decrypt(base64.b64decode(p_obj['value']))
dec_pass = unpad(data, 16).decode()
print(dec_pass)

Answer 2

Full Working Code with MAC Validation

Adding to Gonzalo's submission, Laravel's encrypted message is a base64 json-encoded array consisting of the following key pairs:

[
      'iv' => 'generated initialization vector (iv)',
      'value' => 'encrypted, base64ed, signed value',
      'mac'  => 'message authentication code (mac)'
]

The 'value' is signed using a message authentication code (MAC) to verify that the value has not changed during transit.

The MAC extracted from the payload (encrypted message) should be checked against the mac extracted from the 'value' (this can be done using the key, iv, and value). Laravel's encryption scheme can be found on GitHub: src/Illuminate/Encryption/Encrypter.php

Referencing a discussion thread on Laravel, I traced a partial solution on Github: orian/crypt.py (which is a fork of fideloper/crypt.py).

I have forked off of Orian's code and fixed an input parameter issue. The code works as expected as long as the encryption key (passed in as an input to decrypt()) is base64 decoded and does not include the 'base64:' that is typically prepended to the APP_KEY environmental variable string assignment found in the .env file.

Solution: pilatuspc12ng/crypt.py

The code snippet of the crypt.py is shown below:

import base64
import json
from Crypto.Cipher import AES
from phpserialize import loads
import hashlib
import hmac


def decrypt(payload, key):
    """
    Decrypt strings that have been encrypted using Laravel's encrypter (AES-256 encryption).
    Plain text is encrypted in Laravel using the following code:
    >>> ciphertext = Crypt::encrypt('hello world');
    The ciphertext is a base64's json-encoded array consisting of the following keys:
       [
          'iv' => 'generated initialization vector (iv)',
          'value' => 'encrypted, base64ed, signed value',
          'mac'  => 'message authentication code (mac)'
       ]
    The 'value' is signed using a message authentication code (MAC) so verify that the value has not changed during
    transit.
    Parameters:
    payload (str): Laravel encrypted text.
    key (str): Encryption key (base64 decoded). Make sure 'base64:' has been removed from string.
    Returns:
    str: plaintext
    """

    data = json.loads(base64.b64decode(payload))
    if not valid_mac(key, data):
        return None

    value = base64.b64decode(data['value'])
    iv = base64.b64decode(data['iv'])

    return unserialize(mcrypt_decrypt(value, iv, key)).decode("utf-8")

def mcrypt_decrypt(value, iv, key):
    AES.key_size=128
    crypt_object=AES.new(key=key,mode=AES.MODE_CBC,IV=iv)
    return crypt_object.decrypt(value)

def unserialize(serialized):
    return loads(serialized)

def valid_mac(key, data):
    dig = hmac.new(key, digestmod=hashlib.sha256)
    dig.update(data['iv'].encode('utf8'))
    dig.update(data['value'].encode('utf8'))
    dig = dig.hexdigest()
    return dig==data['mac']

Answer 3

I notice this haven't been active for a while but I'm trying to do the same and can't seem to make it work.

What I noticed is that the encoded password string stored by Laravel is a base 64 encoded json object, which wasn't taken into consideration in the original question:

pass_obj = base64.b64decode('eyJpdiI6ImdxY0VcLzFodmpISFV4allSWmJDdEpRPT0iLCJ2YWx1ZSI6IkxXd0ZJaUd2bTUweW5pNm0wUjQwOFM2N1wvWEs5SlYrNB4xNlR7Qkh1U3FvPSIsIm1hYyI6Ijc5ZWM0YTYxYjljZGFiNzgwNjY2NDU1ZmQ5Yjc1ZmJlOGU4NzBkMjQzMzA3MmVhYzE3NzY4ZmU1MWIyMjZlOTQifQ==')
print(pass_obj)
>>> b'{"iv":"gqcE\\/1hvjHHUxjYRZbCtJQ==","value":"LWwFIiGvm50yni6m0R408S67\\/XK9JV+4\x1e16T{BHuSqo=","mac":"79ec4a61b9cdab780666455fd9b75fbe8e870d2433072eac17768fe51b226e94"}'

From that you can get the IV and the encrypted value, both seem to be base64 encoded. But I still get a decoding error at the end like;

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xfa in position 0: invalid start byte

Here is my complete code;

password = 'eyJpdiI6ImJGNDNNZjN3YWtpcDQ5VEJVXC9IazF3PT0iLCJ2YWx1ZSI6IkNVRW1VQUY1dXArYlFkU3NlY1pnZUE9PSIsIm1hYyI6ImM3ODk0NWQ0NjgxMzM4YjE0M2JhN2MzZWRmOWEwMWJiMjI2Y2FhYmUxYjFhYzAyYjY4YWZkZGE3N2EyMDYwNWYifQ=='
key = 'some secret key that i can't share'.encode()
p_obj = json.loads(base64.b64decode(password).decode())
decobj = AES.new(key, AES.MODE_CBC, base64.b64decode(p_obj['iv']))
data = decobj.decrypt(base64.b64decode(p_obj['value']))
print(data)
>>> b'l\xee:f\x9eZ\x90rP\x99\xca&@\x1d1\x9f'
data.decode()
>>> Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xee in position 1: invalid continuation byte

@Pecans did you ever figure this out?

Thank you.

---

Full working code EDIT

I fugured it out, I had a problem with my key initially. So here's the full snippet for future reference;

import base64
import json
from phpserialize import unserialize
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad

key = b'my secret key'
enc_pass = 'eyJpdiI6ImJGNDNNZjN3YWtpcDQ5VEJVXC9IazF3PT0iLCJ2YWx1ZSI6IkNVRW1VQUY1dXArYlFkU3NlY1pnZUE9PSIsIm1hYyI6ImM3ODk0NWQ0NjgxMzM4YjE0M2JhN2MzZWRmOWEwMWJiMjI2Y2FhYmUxYjFhYzAyYjY4YWZkZGE3N2EyMDYwNWYifQ=='

p_obj = json.loads(base64.b64decode(password).decode())
decobj = AES.new(key, AES.MODE_CBC, base64.b64decode(p_obj['iv']))
data = decobj.decrypt(base64.b64decode(p_obj['value']))
dec_pass = unserialize(unpad(data, 16)).decode()

You will have the decrypted password in dec_pass.

Note that sometimes Laravel generates the key in base64. In that case the string will be something like base64:sdfsdjfhjsdf32, then you have to decode first.

Cheers!

Answer 4

Question: ...trying to decrypt that data in Python but I keep getting errors about key length

I can use your key, in the code of the linked answer, after doing .b64decode(....
The example code .encode(... and decode(... works as expecte.
Conclusion: There is nothing wrong, with your Key!

key = b"/AZejP0lh3McL/+Vy5yZcADdTcR65qnx5Jqinuw7raK="
key = base64.b64decode(key)

---

But with your code, I got TypeError, related to the IV parameter:

  expect_byte_string(iv)
File "/usr/local/lib/python3.4/dist-packages/Crypto/Util/_raw_api.py", line 172, in expect_byte_string
  TypeError: Only byte strings can be passed to C code

Fixed with IV = 16 * '\x00'.encode(), results in ValueError, related to enc:

  data = decobj.decrypt(base64.b64decode(enc))
File "/usr/local/lib/python3.4/dist-packages/Crypto/Cipher/_mode_cbc.py", line 209, in decrypt
  ValueError: Error 3 while decrypting in CBC mode

This leads to github issues:10

Error 3 means "ERR_NOT_ENOUGH_DATA"

According to the linked GitHub page, you have to reread the documentation, about padding data while you are encoding.

---

Working example from GitHub:

import base64
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad

key = b"/AZejP0lh3McL/+Vy5yZcADdTcR65qnx5Jqinuw7raK="
key = base64.b64decode(key)

BLOCK_SIZE = 32
encryption_suite = AES.new(key, AES.MODE_CBC, b'This is an IV...')
cipher_text = encryption_suite.encrypt(pad(b'A really secret message...', BLOCK_SIZE))

decryption_suite = AES.new(key, AES.MODE_CBC, b'This is an IV...')
print(unpad(decryption_suite.decrypt(cipher_text), BLOCK_SIZE).decode())
>>> A really secret message...

Tested with Python: 3.4.2