If you look at the SecurID wikipedia[1] page, in the references you can find a paper discussing two factor authorization in 1996[1]. Also, it's not defining two factor authentication, it assumes the reader knows what it is.<p>[1]: <a href="http://en.wikipedia.org/wiki/SecurID" rel="nofollow">http://en.wikipedia.org/wiki/SecurID</a><p>[2]: <a href="http://www.homeport.org/~adam/dimacs.html" rel="nofollow">http://www.homeport.org/~adam/dimacs.html</a>