Legality and license choice for reverse-engineered project
<p>I reverse engineered (by sniffing+x32dbg) part of the protocol for a board game client in order to build an alternative client on top of it while still using the official servers. I open-sourced the work so that others can contribute to it as well. I'm based in the EU and the product owners are based in China.</p>
<p>Is this legal? And if so, what license is appropriate for it?</p>
<p>Note: I'm not benefiting commercially from this work.</p>

<h2>Check your license!</h2>
<p>By operating the original client, you might have agreed to a license, the EULA. Check that license for what it says about you being allowed to do with the product.</p>
<p>In a recent case of <a href="https://www.courtlistener.com/docket/60204895/bungie-inc-v-elite-boss-tech-incorporated/" rel="noreferrer">Bungie vs. Elite Boss Tech</a>, a US court found in a <a href="https://ia804501.us.archive.org/23/items/gov.uscourts.wawd.302469/gov.uscourts.wawd.302469.75.1.pdf" rel="noreferrer">default judgment</a> that a certain cheat software that would interact with both the game's client and the company's servers among other things did...</p>
<ul>
<li>constitute copyright infringement [as a derivative work]</li>
<li>was a breach of contract [formed by the EULA and agreeing to the Terms of Service for the game]</li>
<li>was interference with Contractual allegations [of other users that obtained the software]</li>
</ul>
<p>However, not all internet games or experiences are locked down like that. Other companies do offer an open API set or terms under which a client's software may be modified. As a very generous example, <a href="https://www.lindenlab.com/" rel="noreferrer">LindenLabs</a> does for its SecondLife Virtual World, <a href="https://wiki.secondlife.com/wiki/APIs_and_Web_Services_Portal" rel="noreferrer">for which they provide not just the framework</a>, but also <a href="https://secondlife.com/corporate/third-party-viewers" rel="noreferrer">the terms under which you are allowed to make a third party <em>Viewer</em></a></p>
<p>Sometimes, the Terms of service are rather hidden. For example, the <a href="https://senseis.xmp.net/?FoxWeiqi" rel="noreferrer">Chinese Go platform Fox Weiqi</a> operates in china. To get to the terms of service, you need to download the free client, go to <em>Settings</em> (via the cog), then choose 野狐围棋用户协议, which is Chinese for Wild Fox Go User Agreement. This links to <a href="https://edu.foxwq.com/complex/useragreement.html" rel="noreferrer">https://edu.foxwq.com/complex/useragreement.html</a>. The user agreement is of course in Chinese, but Google Translate manages to get that to English. It contains the following clause:</p>
<blockquote>
<p>7.2 Unless permitted by law or with the written permission of Yehu, you shall not engage in the following acts during the use of this software:</p>
<p>( 1 ) Delete the copyright information on the software and its copies;</p>
<p>( 2 ) <strong>Reverse engineer, reverse assemble, reverse compile the software</strong>, or try to find the source code of the software in other ways;</p>
<p>( 6 ) Log in or use Yehu Go and its services <strong>through third-party software</strong>, plug-ins, plug-ins, systems not authorized by Yehu, or make, publish, and disseminate the above tools;</p>
<p>( 7 ) <strong>Interfering with the software</strong> and its components, modules, and data <strong>by</strong> itself or authorizing others or <strong>third-party software</strong></p>
</blockquote>
<p><a href="https://ironcladapp.com/journal/contracts/terms-and-conditions-legally-binding/" rel="noreferrer">While it takes a court to see if the terms hold water and are actually enforceable because of how the EULA is offered</a>, the face value of those clauses is, that it is forbidden unless you have a specific law that allows such or you obtain written permission.</p>
<p>With that kind of possible liability that might cost millions, there might be serious legal problems. <strong>Read your license agreement and terms of service</strong> and consult a lawyer.</p>

licensing open-source-software