How to decrypt Zend2 encrypted data? - php

Question

I'm using Zend2 Crypt module to encrypt a data. Here's my code.
$cipher = BlockCipher::factory('mcrypt', array(
'algorithm' => 'aes',
));
$cipher->setKey('mypassphrase');
$encrypted = $cipher->encrypt('Hey, I am the secret data');
Cool, it works well! Now, I need to decrypt that $encrypted data (Hey, I am the secret data) in Python.
I am using pycrypto to do that. What the steps to decrypt data outside my PHP environment?
from Crypto.Cipher import AES
import base64
import hashlib
password = 'mypassphrase'
key = hashlib.sha256(password).digest()
decoded = base64.standard_b64decode(encrypted)
cipher = AES.new(key, AES.MODE_CBC)
data = cipher.decrypt(decoded)
I need to specify an IV because Zend uses MODE_CBC by default. How can I specify it in my Python code?
Here's the Zend2 documentation:
The output of the encryption is a string, encoded in Base64 (default), that contains the HMAC value, the IV vector, and the encrypted text. The encryption mode used is the CBC (with a random IV by default) and SHA256 as default hash algorithm of the HMAC. The Mcrypt adapter encrypts using the PKCS#7 padding mechanism by default. You can specify a different padding method using a special adapter for that (Zend\Crypt\Symmetric\Padding). The encryption and authentication keys used by the BlockCipher are generated with the PBKDF2 algorithm, used as key derivation function from the user’s key specified using the setKey() method.
Can someone help me to adapt my Python code to decrypt the data?
Thanks

Answer 1

I found a way to decrypt the data encrypted by Zend2. Here's my code:
from base64 import b64decode
from Crypto import Random
from Crypto.Cipher import AES
from Crypto.Hash import SHA256, HMAC
from Crypto.Protocol.KDF import PBKDF2
# The hmac starts from 0 to 64 (length).
hmac_size = 64
hmac = data[:hmac_size]
# The cipher text starts after the hmac to the end.
# The cipher text is base64 encoded, so I decoded it.
ciphertext = data[hmac_size:]
ciphertext = b64decode(ciphertext)
# The IV starts from 0 to 16 (length) of the ciphertext.
iv = ciphertext[:16]
# The key size is 256 bits -> 32 bytes.
key_size = 32
# The passphrase of the key.
password = 'mypassphrase'
# The key is generated using PBKDF2 Key Derivation Function.
# In the case of Zend2 Crypt module, the iteration number is 5000,
# the result length is the key_size * 2 (64) and the HMAC is computed
# using the SHA256 algorithm
the_hash = PBKDF2(password, iv, count=5000, dkLen=64, prf=lambda p, s:
HMAC.new(p, s, SHA256).digest())
# The key starts from 0 to key_size (32).
key = the_hash[:key_size]
# The hmac key starts after the key to the end.
key_hmac = the_hash[key_size:]
# HMAC verification
hmac_new = HMAC.new(key_hmac, 'aes%s' % ciphertext, SHA256).hexdigest()
if hmac_new != hmac:
raise Exception('HMAC verification failed.')
# Instanciate the cipher (AES CBC).
cipher = AES.new(key, AES.MODE_CBC, iv)
# It's time to decrypt the data! The ciphertext starts after the IV (so, 16 after).
data = cipher.decrypt(ciphertext[16:])
Mission succeeded!