VolodyA! V Anarhist wrote:
> Brian Mearns wrote:
>> On Thu, Sep 10, 2009 at 6:54 AM, SmallSister development
>> <smallsis...@xs4all.nl> wrote:
>>> Brian Mearns wrote:
>>>> I understand the basic architecture of Freenet and how it protects
>>>> contributors, but I'm concerned that the files themselves might
>>>> contain identifying information about the source of the file. In
>>>> particular, for audio files such as MP3, Ogg Vorbis, and Flac. Does
>>>> anyone have any information on making sure there are no
>>>> "fingerprints" left on these files when posting?
>>> There is no way to be certain. There could be a future algorithm piecing
>>> together just enough bits from a file to identify you. Word frequency
>>> analysis has been used to discern likely writers of a plain text file.
>>> Yes, you can avoid stupid mistakes by checking for "known signatures"
>>> and removing them, but that is something that would be different for
>>> different file types (ogg would be somewhat different from mp3; but doc
>>> and pdf require totally different approaches.) It would be useful to
>>> have tools that can identify and remove watermarks and Freenet would be
>>> a great place to publish them (with source code please!)
>> Bugger, I didn't even think of steganographic watermarks (shame on
>> me), I was thinking more in terms of meta data known to be stored with
>> various file formats (like ID3 tags), but this seems to be more
>> complicated than I expected. Thanks for the insight.
> For audio and video the best approach could be to take the streams and remux
> them into the same container type, then to copy only the metadata which the 
> user
> knows about (for example some audio files have autogain settings, etc).
> You would still have a potential for watermarking, as Peter already pointed 
> out,
> and these watermarks will become more and more common as Internet Music Shop
> software develops (this is not to assume that internet shops is the only 
> source
> of watermarked audio, other groups can watermark a file, this is most 
> dangerous
> in countries where freenet is illegal(*)).
I have heard noticed that multiple rips of the same CD can produce
different .wav files; some of the differences are caused by the
CD-player firmware and some caused by scratches/defects on the CD. Add
some compression artefacts of the mp3 encoder (subtle algorithm
differences between implementations) and you're very likely able to
identify each mp3 uniquely. Even re-encoding may be detectable.
NOTE: this is all without explicitly inserting a watermark.

Remuxing and detection and removal of "steganographic" watermarks is
likely to bring you 95% of the way; which could be good enough.
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