PhotoJoin, a photo synchronization tool

(November 4, 2012)

In this post, I’ll present a solution to a common problem that occurs quite often nowadays: Merging photos from multiple people into one continuous, consistent stream. It is definitely not the first solution to that problem, but since I couldn’t find a tool that solves this in exactly the way I want, I just did it myself, as usual ;)
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Fake screen resolutions in kkapture

(September 27, 2011)

(Disclaimer: This posting is likely of no interest to people outside of the demoscene :)
The small tool kkapture by ryg of Farbrausch is the only sane way to get a video dump of demos, intros and similar stuff. By grabbing all video and audio output directly from their respective APIs (OpenGL/Direct3D and WinMM/DirectSound) and simulating a fixed time base for the client application, it produces perfect-quality smooth video files suitable for Blu-ray Discs, for example. kkapture doesn’t alter the demos in any other way, though – in particular, the screen setup code from the demos is left untouched, with the result that it’s not possible to kkapture most demos in resolutions higher than the display currently attached to the computer. I did a little modification to kkapture’s code that changes this and allows things like 8-megapixel kkaptures.
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Real Steganography with TrueCrypt

(February 24, 2011)

Disclaimer: This article has been written at a time when TrueCrypt was still a viable encryption software. This is no longer the case. TrueCrypt has been discontinued and everybody who has been using it should use one of the maintained forks like VeraCrypt instead.
That being said, this article mostly deals with TrueCrypt as a file format, not the application itself. However, the newer forks (and VeraCrypt in particular) use the same file format, so everything in this article is applicable to VeraCrypt as well. So, when this article talks about TrueCrypt and .tc files, you can just mentally replace this with VeraCrypt and .vc files.

You probably know TrueCrypt, the perhaps most popular tool for encrypting filesystems. As an alternative to full filesystem or even full disk encryption, TrueCrypt can also work with filesystems inside encrypted container files. These are files that look like they’re full of purely random data, but when provided the correct decryption key, they reveal their true contents: A FAT or NTFS filesystem full of your secret data.

In addition to this basic functionality, TrueCrypt also offers a simple form of steganography. For the uninformed, steganography is the term for techniques that conceal the existence of secret data. This means that the secret information is hidden inside another unsuspicious piece of data. TrueCrypt does support this with its »hidden volume« feature. If this is used, a container can be opened with two different keys: The first not-so-secret key opens the »outer volume« with not-so-secret data and a second really secret key opens the hidden volume with the real secrets. There are two problems with this approach, though: First, it’s very simple to destroy the hidden volume since it’s embedded in the outer volume’s data area without proper marking in the outer volume filesystem’s meta-data (otherwise they would give away the presence of the hidden volume). This means that you can overwrite the hidden volume just by putting enough files inside the outer volume. TrueCrypt can protect the hidden volume when mounting the outer volume, but for this to work, you need to provide the hidden volume’s key.

The second issue with TrueCrypt’s approach to steganography is that TrueCrypt container files are just large files with random data and as such, they’re easily detectable. You can disguise them by giving them unsuspicious filenames – pagefile.sys or hiberfil.sys in a drive’s root directory are good candidates on Windows systems, for example. But then again, even these filenames are highly suspicious when found on removable media. So let’s use the next best thing: video files. These also tend to be very large and offer a good disguise for hidden data, but unfortunately, they are very easy to detect: Just try to play such a pseudo-video file and whatever player you use, it will tell you that something’s wrong.

So what we really want to call it proper steganography is a usable file that can be opened with standard software so it doesn’t raise any suspicion, but when opened in TrueCrypt with the right key, it should reveal the real payload – a filesystem full of secrets. Video files are the natural choice as for this kind of hack: Multi-gigabyte videos are completely common nowadays and encoders are so good that even large differences in bitrate don’t necessarily mean large differences in quality. In other words: A well-encoded fifteen-minute HD video clip of 1 gigabyte can look just as good as a not-quite-as-well encoded 4 gigabyte version. So let’s put the 3 gigs we can save to good use and store secret data there.

Unfortunately, this can’t be done using TrueCrypt directly. However, with a little bit of file format tweaking, it turns out to be possible anyway. In this blog post, I will describe a method of hiding TrueCrypt containers inside QuickTime / MP4 video files.
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Choosing the right video format

(January 31, 2011)

There’s a wide variety of devices out there which are capable of video playback – computers, music players, mobile phones, game consoles, you name it. However, all of them support a different set of formats and there’s no combination to catch them all. So if you want to generate a video, you will always have to pick a format based on a selection of devices that are important to you. To make this a little bit easier, I prepared a little tool for you:

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Video encoder comparison

(February 25, 2010)

There has been some buzz about HTML5 web video lately. I won’t retell the story here, because it’s almost completely political and not technical, while I’m only interested in the technical side of things. One thing that struck me, though, is that many people believe that the two contenders, H.264 and Ogg Theora, are comparative in quality and performance. As someone who implements video codecs for a living, this struck me as quite odd: How can a refined version of an old and crippled MPEG-4 derivate come anywhere close to a format that incorporates (almost) all of the the latest and greatest of video compression research? I decided to give it a try and compare H.264, Theora and a few other codecs myself.
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pdfgen, an image-to-PDF converter tool

(December 14, 2009)

Converting images of scanned documents into proper PDF files is quite a hard task. What I usually want is

  • put the images on a page of a well-defined size (e.g. A4 or Letter)
  • don’t resample the image data
  • have precise control over compression – in particular, I want to use JPEG images as-is, without any recompression

This sounds simple and reasonable, but I’ve yet to find a tool that does exactly that. Adobe Acrobat handles the latter two constraints well, but I don’t know how to set the paper size when importing an image. This is no problem when using a normal vector graphics or page layout tool, but then you usually don’t have much influence on what nasty things the PDF output code does to your images. Furthermore, you mostly end up with useless cruft in the PDF files, like XML metadata or even fonts (even though there’s not a single letter of text anywhere in the document). So I decided to end this mess once and for all and write my own image-to-PDF converter. Here it is: pdfgen.
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Proposal: A file system for Live CDs

(August 20, 2009)

CDs or DVDs containing a full Linux system for installation, testing, repair or other special purposes are quite common these days. Chances are high that people make their first steps with the Linux, BSD or Solaris operating system using these so-called Live CDs: They are convenient (no need to install the OS), they are safe (doesn’t write anything to disk unless you really want it to) … but they are slow. Booting from a Live CD like Knoppix or the Ubuntu Desktop CD takes ages and makes you wonder if your CD/DVD drive will actually survive that whole operation, considering that it is permanently seeking. And even if you made it to the desktop, you’ll still have to be patient if you intend to open any application, because the drive has to spin up again and load libraries and data for whatever program you start. Or even worse: In the modern GUI-based environments you have to wait for icons to load even if you just click on a launcher menu. As useful as those Live CDs might be, this a major source of annoyance.

In this post, I will present a method to solve this problem. I do not claim to be the first one to invent it – in fact, I refuse to believe that no one had this idea before me.
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NanoJPEG: a compact JPEG decoder

(April 29, 2009)

If you followed my works, you know that I like compact, single-file implementations of decoders for various media formats, and where such a thing doesn’t exist, I tend to write or at least port one myself. Now I’d like to add the third format to that list: Baseline JPEG images.
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Four generations of iPod nanos compared

(February 16, 2009)

Over the last few years, I bought one specimen of all four generations of Apple’s iPod nano media player, mainly to make rePear compatible with each new model. (In fact, rePear’s main development target are iPod nanos.) Here are my thoughts about the benefits and drawbacks of each generation.
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Late Christmas Gift: A Wallpaper Generator

(December 30, 2008)

This post and the software described in it were originally planned to be released before or on December 24th, but I didn’t manage to finish either. So consider my random wallpaper generator as a late christmas gift.

The idea for this program was born rather quickly: I wanted to have some nice and fancy desktop background images (»wallpapers«), and I wanted them to change every day. This is nothing new, I already did that in the past by writing scripts that choose one random image from a certain directory, scale them to fit on the screen and use them as wallpaper. This approach is simple and common; it’s supported by all major desktop enviroments now, if I remember correctly. However, it has two drawbacks: First, you need to update the pool of available images every now and then so it doesn’t get boring. Second, everyone who’s looking at your desktop (maybe because you do a presentation, or you want to show something, or you requested some help) will be distracted by the wallpaper. You’ll likely end up talking about the things that can be seen on the wallpaper rather than the real subject.
A proper solution for this is having a generator that procedurally creates random images that are suitable as background images – that is, nice, soothing images that don’t distract too much. Basically the kind of background images that shipped as default in Ubuntu up to 7.10 and Mac OS X up to 10.4. My program is trying to do exactly that.
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