In [[cryptography]], the '''S-1 block cipher''' was a [[block cipher]] posted in [[source code]] form on [[Usenet]] on [[11 August]][[1995]].<ref>{{cite newsgroup |title=this looked like it might be interesting |author=Anonymous|date=1995-08-09 |newsgroup=sci.crypt |message-id=40b50l$oa8@utopia.hacktic.nl |url=http://groups.google.com/group/sci.crypt/msg/68a25b11b28c6e8e?dmode=source |access-date=2009-05-28}}</ref> Although incorrect security markings immediately indicated a [[hoax]], there were several features of the code which suggested it might be leaked source code for the [[Skipjack encryption algorithm(cipher)|Skipjack]] cipher, which was still [[classified information|classified]] at the time.
However once [[David A. Wagner|David Wagner]] had discovered a severe<ref>[http://groups.google.com/group/sci.crypt.research/browse_thread/thread/e4dd336ab5385cfb/a4acecc197ec93dc Cryptanalysis of S-1], Aug 27, 1995, </ref> [[product defect|design flaw]], involving the [[key schedule]] but not the underlying round function, it was generally accepted as being a hoax - buthoax—but one with an astonishing amount of work behind it. [[Bruce Schneier]] noted that S-1 contained a feature never seen before in the open literature; a G-table that results in key and data dependent rotation of S-boxes to use in a given round.<ref>[https://groups.google.com/d/msg/sci.crypt/l4nsjVu27lU/LIycdmVxJZ0J The S-1 Algorithm], Sep 6, 1995,</ref> When Skipjack was eventually declassified in [[1998]], it was indeed found to be totally unlike S-1.
==References==
"S-1" also was the United States's government codename for the [[atomic bomb]]. Throughout many government papers, [[Henry Stimson]] and others within the State Department referred to the bomb as S-1.
