The National Security Agency has declassified an eye-opening pre-history of computers used for code-breaking between the 1930s and 1960s. The report, entitled It Wasn’t All Magic: The Early Struggle to Automate Cryptanalysis (pdf), it is available on the Government Attic web site. Government Attic has also just posted a somewhat less declassified NSA compendium from 1993: A Collection of Writings on Traffic Analysis. Special thanks and courtesy of GovernmentAttic.org.
Wasn't All Magic: The Early Struggle to Automate Cryptanalysis [362 Pages, 49MB]