The scenario is the following: a proprietary software can save files in its own file format. I want to build a free/open-source software capable of decoding those files for further processing.

Given that there is no documentation for the file format, I create a few files and reverse engineer them. After experimenting with them and after understanding the rules behind them, I write my software. Note that I only worked with the files, I didn't attempt to disassemble the proprietary software itself.

Now, supposing there are no patents covering the file format, can I release my software to the public? Are patents the only thing I should worry about? Can the software license restrict what I can do with the files it produces?


2 Answers 2


Disclaimer: IANAL, and this strikes me as an area where the principle that 'anyone can sue anyone' might be sadly relevant.

This will depend on the nature of the intellectual property of the file format. So, let's imagine that there is proprietary software package that produces and consumes this format, and that the producers of that software considers the file format to be proprietary, and perhaps even 'trade secret'. Very likely, their license will not permit reverse engineering. Depending on whether this license is a click-through, a shrink-wrap, or a real, signed, SLA, and depending on the jurisdiction, this lack of permission may be enforceable, or it may not.

However, if the owner is trying to prevent reverse-engineering, and you have reverse-engineered, and you make a public spectacle of that fact, you are painting a 'please sue me' sign on your forehead. Will you be sued? Who knows? It depends on how seriously the particular vendor takes this question.

Now, I've tried to paint the most scary scenario here that I could, since you didn't provide details. Maybe the company in question doesn't care, or doesn't exist any longer. Maybe the format is an open secret. Maybe their license doesn't try to prevent this. But the situation I described is fairly typical.


If the copyright for the files is owned by you (the project creator) or owned by the person using your software, then I believe patents are your only concern.

You did not make a copy of the proprietary software, so nothing to worry about with regard to copyright.

Your users are allowed to do anything they choose with the files, because they own them. Or if you own the file, then you are allowed to give other people permission to do things with them (providing software issues an implied license for users to use that software with your files). So again, nothing to worry about.

If this was something like music or a movie or a game or a font where the user typically only has a license to use the files in a limited fashion, then the DMCA would be a concern.

Based on the limited details you've provided I think you are fine. Also, keep in mind that as long as you're likely to win your court case it should be fairly easy for an open source project to get free legal help if somebody tries to file an invalid lawsuit against you. There are plenty of non-profit organisations that provide legal help to open source projects.

  • Could you indicate how the DMCA comes into the picture here?
    – Martijn
    Aug 22, 2015 at 18:24
  • @Martijn If the file is a Taylor Swift song in a proprietary format (rather than a standard one like MP3), and the user has a license to play that song using their headphones but your program allows the song to be played using their headphones or speakers, then you would be facilitating the breach of an "access control" under the DMCA. There other ways you could breach it too, the DMCA is a ******* minefield of over-reaching legislation. I clarified that it doesn't apply to this question in comments and so decided to only touch on it briefly in my answer. Aug 22, 2015 at 21:19

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