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I recently made a post about an audio steganography program and had another concern I thought I might ask. I understand that most music has DRM in them. If I hide secret files in audio files with DRM can an adversary see that I have hid files in it because of that? Also, wouldn't this be breaking the law as well because I'm technically modifying that file?

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  • Hide secret files "with DRM"? What does that mean? As for whether or not this breaks the law, this depends on your jurisdiction. We are not lawyers and you need to get your own if you want legal questions answered.
    – forest
    Commented May 23, 2018 at 23:49
  • What I meant was, Isn't DRM supposed to detect whether or not a file has been modified or distributed in any way?
    – user178802
    Commented May 23, 2018 at 23:54
  • No, not really. DRM is simply a way to prevent the playback of unauthorized files. For something like a plain music file, it may make it so that iTunes will refuse to play unauthorized files. In fact, in order to modify data, you often have to strip the DRM and turn it into a regular audio file.
    – forest
    Commented May 23, 2018 at 23:58

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You probably mean watermark rather than DRM. DRM forces you somehow to use subject in accordance to the license.

Watermark (signal modified using the steganography) can be supporting technology for DRM (i.e. you can't hear audio when PlayStation detects that movie is not legal - based on audio steganography watermark it prevents you to watch the movie).

As far as I know, it is very hard to find steganography data in any kind of media, because you have to know the algorithm used to encode the data to the signal.

What you definitely can do is you can compare original signal with modified one and based on these data to try to analyse if there is some pattern in it.

Good math guy can maybe make it :)

Regarding the law (European one), when I buy a CD nobody can tell me anything when I make a backup copy in any form (i.e. MP3). Also, when I put some hidden data to it it is my problem.

For distribution it will depend on the license the owner of rights will provide. If they will say you can't modify, you can't do that ;)

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  • I'm not aware of any watermarking that is actually used to detect unauthorized playback. As far as I know, watermarking is only used to track down individual pirates (or the source account from which a pirated movie came)
    – forest
    Commented May 24, 2018 at 0:04
  • Try to play an illegally downloaded movie, ideally released by Columbia Pictures, on PlayStation over DLNA ;)
    – Fis
    Commented May 24, 2018 at 0:08
  • Well of course they use DRM (and will likely even refuse to output nearly anything over HDMI unless HDCP is enabled), but do they actually use watermarking for detection, not just non-repudiation?
    – forest
    Commented May 24, 2018 at 0:09
  • See this techspot.com/news/… and this screenshot from PS3 i.imgur.com/gUuUAuD.jpg
    – Fis
    Commented May 24, 2018 at 0:15
  • Oh that's interesting. Well, I learned something today!
    – forest
    Commented May 24, 2018 at 0:19

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