1
by Benson, Robert Louis
Published 1997
Center for Cryptologic History, National Security Agency

2
by Foot, M. R. D.
Published 2004
Routledge

4
by Hargreaves, E. L.
Published 2013
Routledge

5
by Kahn, David
Published 2014
CRC Press, Taylor & Francis Group

6
Published 2014
Center for Cryptologic History

7
by Parker, Frederick D.
Published 1993
National Security Agency, Center for Cryptologic History