&gt; why was this classified??<p>It wasn&#x27;t, it isn&#x27;t clear to me what it even has to do with NSA. It was published in Journal of the ACM, Volume 12, 1965: <a href="http:&#x2F;&#x2F;dl.acm.org&#x2F;citation.cfm?doid=321264.321274" rel="nofollow">http:&#x2F;&#x2F;dl.acm.org&#x2F;citation.cfm?doid=321264.321274</a>.<p>Actually the -1+i base was proposed by S. Khmelnik a year earlier (at least according to Wikipedia, I can&#x27;t read Russian...)