See also Martin Hellman&#x27;s oral history on trap doors: <a href="https:&#x2F;&#x2F;conservancy.umn.edu&#x2F;bitstream&#x2F;handle&#x2F;11299&#x2F;107353&#x2F;oh375mh.pdf?sequence=1" rel="nofollow">https:&#x2F;&#x2F;conservancy.umn.edu&#x2F;bitstream&#x2F;handle&#x2F;11299&#x2F;107353&#x2F;oh...</a>