The Feistel function of the <a href="https://en.wikipedia.org/wiki/Blowfish" class="extiw" title="w:Blowfish">Blowfish</a> cipher.
Benjamin D. Esham (<a href="//commons.wikimedia.org/wiki/User:Bdesham" title="User:Bdesham">bdesham</a>)
Own work  by <a href="//commons.wikimedia.org/wiki/User:Bdesham" title="User:Bdesham">bdesham</a> using:  <a href="https://en.wikipedia.org/wiki/Inkscape" class="extiw" title="w:Inkscape">Inkscape</a>. Own work based on: <a href="//commons.wikimedia.org/wiki/File:Blowfish_(cipher)_InfoBox_Diagram.png" title="File:Blowfish (cipher) InfoBox Diagram.png">Blowfish (cipher) InfoBox Diagram.png</a> <i>by</i> <a href="//commons.wikimedia.org/wiki/User:Dake~commonswiki" title="User:Dake~commonswiki">Dake</a>.