pycrypto: what am I doing wrong?

[Johannes Bauer]

On 24.10.2013 09:33, Johannes Bauer wrote:
> On 24.10.2013 07:22, Paul Pittlerson wrote:
> 
>> What am I doing wrong?
> 
> You're not reinitializing the internal state of the crypto engine. When
> you recreate "cipher" with the same IV every time, it will work.

Code that works:

#!/usr/bin/python3
import hashlib
from Crypto.Cipher import AES
from Crypto import Random

h = hashlib.new('sha256')
h.update(b'my key')
key = h.digest()

iv = Random.new().read(AES.block_size)
cipher = AES.new(key, AES.MODE_CFB, iv)
txt = 'hello world'

msg = cipher.encrypt(txt)
print(msg)

cipher = AES.new(key, AES.MODE_CFB, iv) # Use *same* IV!
origtxt = cipher.decrypt(msg)
print(origtxt)


Also note that manually deriving a symmetric secret using SHA256 is an
INCREDIBLY bad idea. Have a look at PBKDF2.

Best regards,
Joe

-- 
>> Wo hattest Du das Beben nochmal GENAU vorhergesagt?
> Zumindest nicht öffentlich!
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