Audio steganography

A few thoughts. (It's too early in the morning) D

I'd start by looking for any stego programs. This might help in finding out which program/algorithm was used.

From Wetstone's FAQ

Today we supply algorithms that process the most common image types. They include paletted images such as bmp, gif, and png, and true color images like 24-bit BMP files and lossy compressed images such as JPG. In addition, we have detectors that analyze audio wav file embedding as well.

CD Audio files are of a different format than WAV files so hopefully the above quote is out of date, however they both use PCM (Pulse Coded Modulation).

As you are probably aware, there are several places to hide data on a CD, and it may not be in the Audio data.

I haven't done much in file system steganography so it's beyond me. shock My specialty is MP3 and MP4 files.

It may be possible to find the original audio tracks used to make the CD and make a comparison. The audio on the CD could also have been generated from MP3 files.

If so, the software may be available on the computer and can be used to generate PCM based files for comparison with the Audio on the CD.

Hope this info helps.

Thanks a lot, it helps indeed…

I searched the web to find the original CD but it looks like it is some kind of "homemade" compilation…

As for stego softs, I asked for the PC but it looks like I will never get it jurisdiction problems.

I may end up going through comparison of the songs with … I don't know yet what kind of files ! )

Anyway thanks for the much appreciated help.

I may end up going through comparison of the songs with … I don't know yet what kind of files !

Windows should be able to extract the PCM to PCM WAV files, however;

I searched the web to find the original CD but it looks like it is some kind of "homemade" compilation…

It might have been made from MP3 files. For example, iTunes allows you to make Audio CD collections from your collection of MP3s. Therefore the PCM audio on the CD will be missing certain frequencies.

If you can ascertain if frequencies are missing, ie above 16 K, then you will know that the CD was sourced from MP3s. If not and it appears to be a good quality PCM file, then you may be able to find one of the songs on another Audio CD for comparison.

Also depending on the size of the payload you may be looking for, would depend on where to look, but the LSBs of the PCM data would be a good place to start.

Another thought, check if there are extended periods of silence at the start or end of each song. While this applies to MP3 files, it may not apply to PCM Audio. It's slightly out of my area of expertise.

Happy Hunting

I am facing a case with suspected hidden data into an audio CD … did anyone already deal with that kind of problem ?

Hi )

Just a couple of thoughts; First I'd ask about the source of the CD, and why you believe it has suspected hidden data, if you're able to say (e.g. because of tools found on PC of the issuer, because of how it was being used, because this is part of an exam and you've been told to analyse it, etc)? Depending on the answer to that will likely cause different approaches, which tools may be applicable, how the data may have been hidden (depending on what type/volume of data you believe has been hidden, for example).

There are many ways to hide data on an audio CD. First question, is it 'just' an ordinary audio CD (it could appear as audio CD, but with additional data tracks in unused space, etc), i.e. unless you already know otherwise, in addition to use of stego (or bespoke/corporate) tools to add data 'within' the mp3/wav files used, could the data simply be hidden from normal viewing rather than embedded in the audio track itself. Another area of possible use would be deliberate errors on the created CD, which are automatically corrected during CD read unless this is disabled; such a pattern of errors can also be used to hide information on a CD. Worth checking/searching CD/audio watermarking and data embedding using perceptual techniques.

Hope that helps,

Phil.