AES - Encryption with Crypto (node-js) / decryption with Pycrypto (python)

I'm writing this question + answer because I struggled a lot (maybe because of a lack of experience), got lost in many different ways of encrypting/decrypting things with node or python.

I thought maybe my case could help people in the future.

What I needed to do:

Get data from a form, encrypt them using Crypto (node-js)
Pass the encrypted data in Python and decrypt it using PyCrypto.

I chose to use the AES encryption.

Here is how I started (I'm not gonna go through everything I tried):

I followed the example at the end of this page

Which gave in my case:

(this might be a very bad mix between javascript and coffeescript)

crypto = require "crypto"
[...]
key = "mykeywhatever"
cipher = crypto.createCipher('aes192', key)
cipher.update('string i want to encode', 'binary', 'hex')
encoded_string = cipher.final('hex')
[...]

This worked pretty fine to encode my string.

Then I wrote my python script to decrypt this string, using the readme on PyCrypto's github's page:
```
from Crypto.Cipher import AES
[...]
my_string = data_coming_from_rabbitmq
obj = AES.new('mykeywhatever', AES.MODE_CBC)
obj.decrypt(ciphertext)
[...]
```
This obviously didn't work: in the readme there is an IV but since I didn't gave one in the node script, why would I give one in the python one?

After more googling, I learnt that node's Crypto uses OpenSSL, while PyCrypto apparently doesn't. So I looked into that and found those pages:

So things got complicated, no one is doing the same thing to decrypt data, I got lost, and asked for help.

The answer is what my coworker and I came up with (well, mostly my corworker).

Solution

So we started from the "How can i decrypt... OpenSSL" 's answer.

We needed to modify the encryption script which gave:

crypto = require "crypto"
[...]
var iv = new Buffer('asdfasdfasdfasdf')
var key = new Buffer('asdfasdfasdfasdfasdfasdfasdfasdf')
var cipher = crypto.createCipheriv('aes-256-cbc', key, iv);
cipher.update(new Buffer("mystring"));
var enc = cipher.final('base64');
[...]

iv needs to be 16bytes long, key is 32bytes. And we changed createCipher to createCipheriv.

Back to the python decryption script:

Process was simply reading PyCrypto's documentation, and compare with the code we started from.

Then we decided to just stick to the API, and start from scratch. And it gave:

from base64 import b64decode
from Crypto.Cipher import AES
[...]
iv = 'asdfasdfasdfasdf'
key = 'asdfasdfasdfasdfasdfasdfasdfasdf'
encoded = b64decode('my_encrypted_string')

dec = AES.new(key=key, mode=AES.MODE_CBC, IV=iv)
value = dec.decrypt(encoded)

And it was as simple as that... Hope it'll help some of you!

Update:

As Perseids wrote in the comments of his answer, the IV has to be random and different for every message