Edit Question - KnowledgeHub

Title Body

I'm trying to understand how PyCrypto works to use in a project but I'm not fully understanding the significance of the Initialization Vector (IV). I've found that I can use the wrong IV when decoding a string and I still seem to get the message back except for the first 16 bytes (the block size). Am simply using it wrong or not understanding something? Here's a sample code to demonstrate: import Crypto import Crypto.Random from Crypto.Cipher import AES def pad_data(data): if len(data) % 16 == 0: return data databytes = bytearray(data) padding_required = 15 - (len(databytes) % 16) databytes.extend(b'\x80') databytes.extend(b'\x00' * padding_required) return bytes(databytes) def unpad_data(data): if not data: return data data = data.rstrip(b'\x00') if data[-1] == 128: # b'\x80'[0]: return data[:-1] else: return data def generate_aes_key(): rnd = Crypto.Random.OSRNG.posix.new().read(AES.block_size) return rnd def encrypt(key, iv, data): aes = AES.new(key, AES.MODE_CBC, iv) data = pad_data(data) return aes.encrypt(data) def decrypt(key, iv, data): aes = AES.new(key, AES.MODE_CBC, iv) data = aes.decrypt(data) return unpad_data(data) def test_crypto (): key = generate_aes_key() iv = generate_aes_key() # get some random value for IV msg = b"This is some super secret message. Please don't tell anyone about it or I'll have to shoot you." code = encrypt(key, iv, msg) iv = generate_aes_key() # change the IV to something random decoded = decrypt(key, iv, code) print(decoded) if __name__ == '__main__': test_crypto() I'm using Python 3.3. Output will vary on execution, but I get something like this: b"1^,Kp}Vl\x85\x8426M\xd2b\x1aer secret message. Please don't tell anyone about it or I'll have to shoot you."

Tags (comma-separated) Cancel