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I wouldn't venture to say this doesn't belong on HN since it really is interesting (if it was actually done correctly), but the files available for download are most likely illegal, were most likely created with pirated tools (IDA Pro/Hex-Rays, and yes, as a customer of theirs for over a dozen years I've reported it), and of course, the usual vilification of reverse engineering.

If you're reading this on a desktop or laptop system (rather than a phone), then you are most likely using an "IBM PC Compatible" even if you're using an Intel based Apple, and hence, you're using the fruits of completely legal reverse engineering.

The way to do reverse engineering legally is to have one team reverse engineer the target and completely document how it works. Once it's documented, another disconnected team writes a new implementation from the documentation. This process is how you're using an IBM PC Compatible today, so yes, reverse engineering for compatibility is perfectly legal.

If there is a patented algorithm required, it's not a sure thing. There are most likely compatible ways around the patent, but there's also the fact that the patent is only valid in the US. With open source hosted in some other country, who are you going to sue? The users in the US? --Nope, users are the ones paying for skype.

You might say, "But we forbid reverse engineering in our license!!!"

Contract clauses forbidding reverse engineering are invalid in many countries and jurisdictions, and of course, you also have to prove the other party agreed to the contract/license. With this said, it's very easy to create a international jurisdictional nightmare to render any such contract clause tactically impossible to enforce.

The easiest way to think about this is security research. The folks finding and reporting exploitable flaws in software are obviously reverse engineering it. Occasionally companies have tried to legally go after people who have published security research on their products, but usually this ends very badly for the company. Additionally, doing security research is protected use in some countries and jurisdictions.

In short, competition is good for markets, and competing by studying and mimicking the competition is both normal and legal.

For the "rights" advocates out there, there are legal problems with the three file downloads available:

1.) According to the first file name, the original binaries are being redistributed which may be (and usually is) against the license terms and default rights granted by copyrights.

2.) The IDA Pro database (most likely) contains the entire target binary, so you do have (illegal) redistribution of a copyrighted work. You can load only parts of a target binary into IDA, but that doesn't matter since it is still a portion of the original work. As for whether or not said portion could fall under fair use is debatable (i.e. lawsuit). In general usage, the entire binary is loaded, since without it, you're limited to static analysis (i.e. no debugging).

3.) Decompilation, and to a lesser degree disassembly, are equivalent to "machine translation" in the sense of copyright. Creating a translation is considered creating a "derivative work" and unless you have been given rights to create derivative works, then you're in trouble. One of the comments here on HN claims the "source code" file is the output of the Hex-Rays Decompiler.

I've never used skype and I've never read their license so I don't know if they specifically allow redistribution.

I have no love for skype or microsoft, but if this had been done CORRECTLY by releasing written documentation so an entirely new implementation could be written, then I'd have no problem with it. There are right ways and wrong ways to legally create compatible (open source) software through reverse engineering, and this is a perfect example of the wrong way.

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