["python","encryption","padding","pycrypto","initialization-vector"]
Encrypt and decrypt using PyCrypto AES-256

I'm trying to build two functions using PyCrypto that accept two parameters: the message and the key, and then encrypt/decrypt the message. I found several links on the web to help me out, but each one of them has flaws: This one at codekoala uses os.urandom, which is discouraged by PyCrypto. Moreover, the key I give to the function is not guaranteed to have the exact length expected. What can I do to make that happen? Also, there are several modes, which one is recommended? I don't know what to use :/ Finally, what exactly is the IV? Can I provide a different IV for encrypting and decrypting, or will this return in a different result?
Here is my implementation, and it works for me with some fixes. It enhances the alignment of the key and secret phrase with 32 bytes and IV to 16 bytes: import base64 import hashlib from Crypto import Random from Crypto.Cipher import AES class AESCipher(object): def __init__(self, key): self.bs = AES.block_size self.key = hashlib.sha256(key.encode()).digest() def encrypt(self, raw): raw = self._pad(raw) iv = Random.new().read(AES.block_size) cipher = AES.new(self.key, AES.MODE_CBC, iv) return base64.b64encode(iv + cipher.encrypt(raw.encode())) def decrypt(self, enc): enc = base64.b64decode(enc) iv = enc[:AES.block_size] cipher = AES.new(self.key, AES.MODE_CBC, iv) return AESCipher._unpad(cipher.decrypt(enc[AES.block_size:])).decode('utf-8') def _pad(self, s): return s + (self.bs - len(s) % self.bs) * chr(self.bs - len(s) % self.bs) @staticmethod def _unpad(s): return s[:-ord(s[len(s)-1:])]