Is it legal to write software to convert data from a proprietary format?

Question

I have created a piece of software that converts a proprietary format from the database blob of a large, well known commercial software company into the equivalent open source data type. The large commercial software company states the following on their copyright and trademarks page "This work is protected under United States copyright law and other international copyright treaties and conventions." and links to the DMCA.

I was able to create the software because most details of the format were published in a post on their support forums and the rest I reverse-engineered.

I now wish to open-source my software so others can use it. My question has two parts:

1. Can I open-source this at all without getting sued?
2. Can I refer to the trademarked product the file format came from in my software and documentation? (I'm assuming I can't use it in the name of my software)

I'm in the UK. The large software company is in the US.

Answer 1

There's several different parts to this.

1. Is it legal to reverse engineer the program
2. Is it legal to reverse engineer the format (from files)
3. Is it legal to distribute software that consumes the proprietary format
4. Can you be sued for any of this

---

For #1, EFF has a good FAQ for the US.

Acts in the UK up to 2020 (Brexit) would be covered under EU Directive 2009/24/EC, which makes reverse engineering for compatibility purposes legal in many circumstances (including if you don't have the author's permission to use the software). This article has a good overview.

---

For #2 it's important to know that the output of a program is not copyrighted by the author of a program, although it might be copyrighted by the user who operated the program.

So you should have permission to hold a copy of the files you're inspecting if they contain copyrightable elements (for example, the text inside a .doc file belongs to the person that wrote it).

---

#3 could be illegal if there's a software patent.

Famously the distribution of software that read GIF files was hampered by a patent on the LZW compression method. Another famous example is Microsoft's FAT filesystem, which resulted in lawsuits to companies reading SD cards.

In some of these cases people found restricted ways of reading the formats that were not covered by the patents.

This is extremely dependent on your jurisdiction. You might want to consider publishing your program from a friendly jurisdiction to avoid legal problems

---

#4 is the easiest to answer. You can be sued by anyone for any reason at any time.

Lawsuits involving proprietary formats are usually brought against commercial use of the format (as in the FAT case).

If you're working on open source and a company threatens to sue you and you're confident what you're doing is legal you might want to consider asking for legal assistance from the EFF

Answer 2

The words "proprietary format" are important.

Are you sure the format is proprietary? If it is, then it's likely protected in which case they might have grounds to sue (but that does not mean they would definetly win).

If the format is not proprietary, and so long as you don't share data which is proprietary then I believe you fine.

I'm not a lawyer - but I cite GIF files as an example. They were still protected by the US and some other countries until at least the late 90s and there were various threats to open source linux companies who shared code that used the file format. I'm not aware of anything other than threats and never heard of any company being sued, let alone winning or losing.

Another example that comes to mind is the RedHat ISO format. My understanding is RedHat could not stop anyone from sharing open source, but they could prevent folks from sharing the format they assembled and shared the open source. Again, I am not sure if it was ever tested in any court of law anywhere.