Author: Guy

Statistical Tests for My Audio Based Random Number Generator

In May I’ve written about a way to generate random number from audio noise. Basically it went like this:

  1. Get audio sample from the microphone.
  2. Push the least significant bit to a buffer.
  3. Repeat steps 1-2 until the buffer is full (buffer size == block size for the hash function).
  4. Apply the hash function on the buffer.
  5. Get random bits from the digest.

In order to continue developing this random number generator (RNG), I’ve written a C++ class that simplifies working with it.
Continue reading Statistical Tests for My Audio Based Random Number Generator

Deleting Comments from Tickets in Trac

Spammers apparently love Trac. After trying to fighting spam tickets and later installing the SpamFilter plugin, I’ve managed to control spam tickets in the Open Yahtzee Trac site.. But now spammers started spamming in the ticket comments. The bad news is that Trac (at least in version 0.11) doesn’t have built-in facilities to completely remove ticket comments.


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Audio Based True Random Number Generator POC

Few days ago I came up with an idea to create a true random number generator based on noise gathered from a cheap microphone attached to my computer. Tests showed that when sampling the microphone, the least significant bit behaves pretty randomly. This lead me to think it might be good source for gathering entropy for a true random number generator.
Continue reading Audio Based True Random Number Generator POC

Python’s base64 Module Fails to Decode Unicode Strings

If you’ve got a base64 string as a unicode object and you try to use Python’s base64 module with altchars set, it fails with the following error:

TypeError: character mapping must return integer, None or unicode

This is pretty unhelpful error message also occurs if you try any method that indirectly use altchars. For example:

base64.urlsafe_b64decode(unicode('aass'))
base64.b64decode(unicode('aass'),'-_')

both fail while the following works:

base64.urlsafe_b64decode('aass')
base64.b64decode(unicode('aass'))

While it’s not complicated to fix it (just convert any unicode string to ascii string), it’s still annoying.

URL-Safe Timestamps using Base64

Passing around timestamps in URLs is a common task. We usually want our URLs to be as shortest as possible. I’ve found using Base64 to result in the shortest URL-safe representation, just 6 chars. This compares with the 12 chars of the naive way, and 8 chars when using hex representation.

The following Python functions allow you to build and read these 6 chars URL-safe timestamps:
Continue reading URL-Safe Timestamps using Base64

Hash Puppy 0.2

This is an update for my simple easy-to-use checksum calculator. It supports md4, md5, and sha1 hash functions. I wrote the project as a way to experience and learn Qt.

Changes since the previous version (Hash Puppy 0.1) include ability to abort a checksum calculation and improved GUI responsiveness. Also there were other minor tweaks to make Hash Puppy easier to use.
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Improved FTP Backup for WordPress

This script backups both the database and files of a WordPress blog into a remote FTP server (while keeping a local copy). It’s an update of my WordPress Backup to FTP script. The main changes are auto-detecting database settings and better support for caching plugins (specifically WP-Cache). The new version makes it easier to backup multiple WordPress blogs to the same FTP server.
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“CC Yourself” and Spam

Every good web programmer will note that the following contact form markup is probably flawed

<form>
...
    <input type="hidden" name="to" value="support@example.com" />
...
</form>

as it is likely that if the value of the “to” field changes the message will be sent to the modified address. The problem with this kind of functionality is that it allows a malicious user to send emails from your mail server. More specifically, it can allow spammers to user your benign server t send their spam (and as a side effect you might be flagged as a spammer yourself).

As this case is pretty obvious one doesn’t see many real-life uses of it anymore (but careless programmers used it more often n the past until they learned better). However one can achieve similar goals (spam-wise) by utilizing a common feature in contact forms: the “CC yourself” checkbox.

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Disable Touchpad Tapping in Kubuntu

In Ubuntu (gnome) there is an easy graphical way to disable tapping on the touchpad. However, KDE lacks such thing. But lacking graphical configuration doesn’t mean this should be difficult. All you need is the gsynaptics package. The package provides a small utility called synclient. Now you can disable tapping by doing

 synclient TapButton1=0

To disable the tapping permanently you should use the following to run the command at the start of every KDE session. 

echo "synclient TapButton1=0" > ~/.kde/env/disable-tapping.sh