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

Question

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:

• How can I decrypt something with PyCrypto that was encrypted using OpenSSL?
• Is AES the same in libraries PyCrypto & Node.JS Crypto
• and a lot more...

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).

Answer 1

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