Haynes, John Earl and Harvey Klehr. Venona: Decoding Soviet Espionage in America. New Haven, CT: Yale University Press, 1999. ISBN 0-300-08462-5.
Messages encrypted with a one-time pad are absolutely secure unless the adversary obtains a copy of the pad or discovers some non-randomness in the means used to prepare it. Soviet diplomatic and intelligence traffic used one-time pads extensively, avoiding the vulnerabilities of machine ciphers which permitted World War II codebreakers to read German and Japanese traffic. The disadvantage of one-time pads is key distribution: since every message consumes as many groups from the one-time pad as its own length and pads are never reused (hence the name), embassies and agents in the field require a steady supply of new one-time pads, which can be a logistical nightmare in wartime and risk to covert operations. The German invasion of the Soviet Union in 1941 caused Soviet diplomatic and intelligence traffic to explode in volume, surpassing the ability of Soviet cryptographers to produce and distribute new one-time pads. Apparently believing the risk to be minimal, they reacted by re-using one-time pad pages, shuffling them into a different order and sending them to other posts around the world. Bad idea! In fact, reusing one-time pad pages opened up a crack in security sufficiently wide to permit U.S. cryptanalysts, working from 1943 through 1980, to decode more than five thousand pages (some only partially) of Soviet cables from the wartime era. The existence of this effort, later codenamed Project VENONA, and all the decoded material remained secret until 1995 when it was declassified. The most-requested VENONA decrypts may be viewed on-line at the NSA Web site. (A few months ago, there was a great deal of additional historical information on VENONA at the NSA site, but at this writing the links appear to be broken.) This book has relatively little to say about the cryptanalysis of the VENONA traffic. It is essentially a history of Soviet espionage in the U.S. in the 1930s and 40s as documented by the VENONA decrypts. Some readers may be surprised at how little new information is presented here. In essence, VENONA messages completely confirmed what Whittaker Chambers (Witness, September 2003) and Elizabeth Bentley testified to in the late 1940s, and FBI counter-intelligence uncovered. The apparent mystery of why so many who spied for the Soviets escaped prosecution and/or conviction is now explained by the unwillingness of the U.S. government to disclose the existence of VENONA by using material from it in espionage cases. The decades long controversy over the guilt of the Rosenbergs (The Rosenberg File, August 2002) has been definitively resolved by disclosure of VENONA—incontrovertible evidence of their guilt remained secret, out of reach to historians, for fifty years after their crimes. This is a meticulously-documented work of scholarly history, not a page-turning espionage thriller; it is probably best absorbed in small doses rather than one cover to cover gulp.

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