I spent a little bit of time last night and this morning trying to find some examples for AES encryption using Python and PyCrypto. To my surprise, I had quite a difficult time finding an example of how to do it! I posted a message on Twitter asking for any solid examples, but people mostly just responded with things I had seen before--the libraries that do the encryption, not examples for how to use the libraries.

It wasn't long after that when I just decided to tackle the problem myself. My solution ended up being pretty simple (which is probably why there weren't any solid examples for me to find). However, out of respect for those out there who might still be looking for a solid example, here is my solution:

#!/usr/bin/env python

from Crypto.Cipher import AES
import base64
import os

# the block size for the cipher object; must be 16 per FIPS-197
BLOCK_SIZE = 16

# the character used for padding--with a block cipher such as AES, the value
# you encrypt must be a multiple of BLOCK_SIZE in length.  This character is
# used to ensure that your value is always a multiple of BLOCK_SIZE
PADDING = '{'

# one-liner to sufficiently pad the text to be encrypted
pad = lambda s: s + (BLOCK_SIZE - len(s) % BLOCK_SIZE) * PADDING

# one-liners to encrypt/encode and decrypt/decode a string
# encrypt with AES, encode with base64
EncodeAES = lambda c, s: base64.b64encode(c.encrypt(pad(s)))
DecodeAES = lambda c, e: c.decrypt(base64.b64decode(e)).rstrip(PADDING)

# generate a random secret key
secret = os.urandom(BLOCK_SIZE)

# create a cipher object using the random secret
cipher = AES.new(secret)

# encode a string
encoded = EncodeAES(cipher, 'password')
print 'Encrypted string:', encoded

# decode the encoded string
decoded = DecodeAES(cipher, encoded)
print 'Decrypted string:', decoded

Edit: thanks to John and Kaso for their suggestions, though John's didn't seem to work for me (?)

Edit 2015.12.14: thanks to Stephen for pointing out that the block size for AES is always 16, and the key size can be 16, 24, or 32. See FIPS-197 for more details.

If you plan to use this script, you'll need to have PyCrypto installed on your computer. I have had a difficult time finding this for Windows in the past, so I will mirror the installer that I found over here: http://jintoreedwine.wordpress.com/2008/07/20/python-25-and-encryption-pycrypto-under-windows/. I haven't tried it on Mac OS X yet, but it should be fairly simple to install it. Same goes for Linux.

The output of the script should always change with each execution thanks to the random secret key. Here's some sample output:

$ python aes_encryption.py
Encrypted string: aPCQ8v9WzLM/JusrJPS19K8uUA/34Xiu/ZR+arzl1oM=
Decrypted string: password

$ python aes_encryption.py
Encrypted string: F0cp4hMk8RXjcww270leHnigH++yqysIyPy8Em/qEbI=
Decrypted string: password

$ python aes_encryption.py
Encrypted string: 7gH2QCIPOxXVBjTXrMmdgU2l7Iku5Lch5jpG9OScGZw=
Decrypted string: password

$ python aes_encryption.py
Encrypted string: oJUq0/XHdmYgC3ILgFgF6Tpuo8ZhoEHN9wmnuYvV58Y=
Decrypted string: password

If the comments in the script aren't explanatory enough, please comment and ask for clarification. I will offer any that I am capable of, and I invite others to do the same.

I just had a buddy of mine ask me to write a script that would send an e-mail to you whenever you get an "@reply" on Twitter. I've recently been doing some work on a Twitter application, so I feel relatively comfortable with the python-twitter project to access Twitter. It didn't take very long to come up with this script, and it appears to work fine for us (using a cronjob to run the script periodically).

I thought others on the Internets might enjoy the script as well, so here it is!

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
A simple script to check your Twitter account for @replies and send you an email
if it finds any new ones since the last time it checked.  It was developed using
python-twitter 0.5 and Python 2.5.  It has been tested on Linux only, but it
should work fine on other platforms as well.  This script is intended to be
executed by a cron manager or scheduled task manager.

Copyright (c) 2009, Josh VanderLinden
All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

- Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this
list of conditions and the following disclaimer in the documentation and/or
other materials provided with the distribution.
- Neither the name of the organization nor the names of its contributors may
be used to endorse or promote products derived from this software without
specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""

import twitter
import ConfigParser
import os
import sys
from datetime import datetime
import smtplib
from email.MIMEMultipart import MIMEMultipart
from email.MIMEText import MIMEText
from email.Utils import formatdate

# get the user's "home" directory
DIRNAME = os.path.expanduser('~')
CONFIG = os.path.join(DIRNAME, '.twitter_email_replies.conf')
FORMAT = '%a %b %d %H:%M:%S +0000 %Y'
REPLY_TEMPLATE = """%(author)s said: %(text)s
Posted on %(created_at)s
Go to http://twitter.com/home?status=@%(screen_name)s%%20&in_reply_to_status_id=%(id)s&in_reply_to=%(screen_name)s to post a reply
"""

# sections
AUTH = 'credentials'
EXEC = 'exec_info'
EMAIL = 'email_info'

# make the code a bit "cleaner"
O = lambda s: sys.stdout.write(s + '\n')
E = lambda s: sys.stderr.write(s + '\n')
str2dt = lambda s: datetime.strptime(s, FORMAT)

def get_dict(status):
    my_dict = status.AsDict()
    my_dict['screen_name'] = my_dict['user']['screen_name']
    my_dict['author'] = my_dict['user']['name']
    return my_dict

def main():
    O('Reading configuration from %s' % CONFIG)
    parser = ConfigParser.SafeConfigParser()
    config = parser.read(CONFIG)

    # make sure we have the proper sections
    if not parser.has_section(AUTH): parser.add_section(AUTH)
    if not parser.has_section(EMAIL): parser.add_section(EMAIL)
    if not parser.has_section(EXEC): parser.add_section(EXEC)

    try:
        # get some useful settings from the configuration file
        username = parser.get(AUTH, 'username')
        password = parser.get(AUTH, 'password')

        to_address = parser.get(EMAIL, 'to_address')
        from_address = parser.get(EMAIL, 'from_address')
        smtp_server = parser.get(EMAIL, 'smtp_server')
        smtp_user = parser.get(EMAIL, 'smtp_user')
        smtp_pass = parser.get(EMAIL, 'smtp_pass')

        if '' in [username, password, to_address, from_address, smtp_server]:
            raise Exception('Not configured')
    except Exception:
        E('Please configure your credentials and e-mail information in %s!' % CONFIG)

        # create some placeholders in the configuration file to make it easier
        sections = {
            AUTH: ('username', 'password'),
            EMAIL: ('to_address', 'from_address', 'smtp_server', 'smtp_user', 'smtp_pass')
        }

        for section in sections.keys():
            for opt in sections[section]:
                if not parser.has_option(section, opt):
                    parser.set(section, opt, '')
    else:
        # determine the last time we checked for replies
        try:
            last_check = str2dt(parser.get(EXEC, 'last_run'))
        except ConfigParser.NoOptionError:
            last_check = datetime.utcnow()
        last_check_str = last_check.strftime(FORMAT)

        info = 'Fetching updates for %s since %s' % (username,
                                                       last_check_str)
        O(info)

        # attempt to connect to Twitter
        api = twitter.Api(username=username, password=password)

        # not using the `since` parameter for more backward-compatibility
        timeline = api.GetReplies()
        new_replies = []
        for reply in timeline:
            post_time = str2dt(reply.GetCreatedAt())
            if post_time > last_check:
                new_replies.append(reply)

        count = len(new_replies)
        if count:
            # send out an email for this user
            O('Found %i new replies... sending e-mail to %s' % (count, to_address))
            reply_list = '\n\n'.join([REPLY_TEMPLATE % get_dict(r) for r in new_replies])
            is_are = 'is'
            plural = 'y'
            if count != 1:
                is_are = 'are'
                plural = 'ies'

            params = {
                'is_are': is_are,
                'count': count,
                'replies': plural,
                'username': username,
                'reply_list': reply_list,
                'last_check': last_check_str
            }

            text = """There %(is_are)s %(count)i new @repl%(replies)s for %(username)s on Twitter since %(last_check)s:

%(reply_list)s""" % params

            # compose the e-mail
            msg = MIMEMultipart()
            msg['From'] = from_address
            msg['To'] = to_address
            msg['Date'] = formatdate(localtime=True)
            msg['Subject'] = 'New @Replies for %s' % username
            msg.attach(MIMEText(text))

            # try to send the e-mail message out
            email = smtplib.SMTP(smtp_server)
            if smtp_user and smtp_pass:
                email.login(smtp_user, smtp_pass)
            email.sendmail(from_address,
                           to_address,
                           msg.as_string())
            email.close()

        # save the current time so we know where to pick up next time
        parser.set(EXEC, 'last_run', datetime.utcnow().strftime(FORMAT))

    # write the config
    O('Saving settings...')
    out = open(CONFIG, 'wb')
    parser.write(out)
    out.close()

if __name__ == '__main__':
    main()

Feel free to copy this script and modify it to your desires. Also, please comment if you have issues using it.

I've decided that if I ever want to really understand Linux, I'll have to give as many distributions as possible a chance. In the past, I've tried to use OpenSUSE on my HP Pavilion dv8000 laptop, but it never seemed quite as robust or useful as many other distributions that I've tried on the same machine.

With the recent release of OpenSUSE 11.1, I downloaded the final 32-bit DVD ISO as I normally do for newly released distributions (even if I don't plan on using them--it's an addiction). I proceeded to install the GNOME version of it in a virtual machine to see what all the hubbub was about. Evaluating an operating system within a virtual machine is not the most effective way to do things, but everything seemed fairly solid. As such, and since I have always had difficulties keeping any RPM-based distro around for any length of time, I plan on using OpenSUSE 11.1 through March 2008 (perhaps longer if it grows on me). If it hoses my system, I will go back to something better. If it works, I will learn to use and appreciate it better.

/usr/sbin/install_bcm43xx_firmware
modprobe b43

wget https://a248.e.akamai.net/f/674/9206/0/www2.ati.com/drivers/\
linux/ati-driver-installer-8-12-x86.x86_64.run

zypper in kernel-source gcc make patch

sh ati-driver-installer-8-12-x86.x86_64.run

rm /usr/lib/dri/fglrx_dri.so && ln -s /usr/lib64/dri/fglrx_dri.so \
/usr/lib/dri/fglrx_dri.so

cp /etc/X11/xorg.conf /etc/X11/xorg.conf.orig
aticonfig --initial -f

sax2 -r -m 0=fglrx

display: :0.0  screen: 0
OpenGL vendor string: ATI Technologies Inc.
OpenGL renderer string: ATI Radeon Xpress Series
OpenGL version string: 2.1.8304 Release