Path: csiph.com!usenet.pasdenom.info!news.franciliens.net!fdn.fr!usenet-fr.net!nerim.net!novso.com!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
MIME-Version: 1.0
In-Reply-To: <97dbe3cc-b739-4876-9221-1143dc1b8c73@googlegroups.com>
References: <97dbe3cc-b739-4876-9221-1143dc1b8c73@googlegroups.com>
Date: Thu, 24 Oct 2013 18:07:16 +1100
Subject: Re: pycrypto: what am I doing wrong?
From: Chris Angelico <rosuav@gmail.com>
To: python-list@python.org
Content-Type: text/plain; charset=ISO-8859-1
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.1447.1382598445.18130.python-list@python.org>
Lines: 42
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:57422

On Thu, Oct 24, 2013 at 4:22 PM, Paul Pittlerson <menkomigen6@gmail.com> wrote:
> msg = cipher.encrypt(txt)
>
>>>> '|s\x08\xf2\x12\xde\x8cD\xe7u*'
>
> msg = cipher.encrypt(txt)
>
>>>> '\xa1\xed7\xb8h<l\x7f\xd7\xba\xed'
>
> # etc

Is this strictly the code you're using? AES is a stream cipher; what
you've effectively done is encrypt the text twice, once as a follow-on
message from the other. To decrypt the second, you'll need to include
the first - or treat it as a stream, and decrypt piece by piece.
Untested code:

import hashlib
from Crypto.Cipher import AES
from Crypto import Random

# Shorter version of your key hashing:
key = hashlib.sha256("my key").digest()

iv = Random.new().read(AES.block_size)
cipher = AES.new(key, AES.MODE_CFB, iv)
txt = 'hello world'

msg1 = cipher.encrypt(txt)
msg2 = cipher.encrypt(txt)
# You may need to reset cipher here, I'm not sure.
# cipher = AES.new(key, AES.MODE_CFB, iv)
cipher.decrypt(iv) # Initialize the decrypter with the init vector
print(cipher.decrypt(msg1))
print(cipher.decrypt(msg2))



I don't have pycrypto to test with, but running the same code with
Pike's Crypto module does what I expect here.

ChrisA