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Acknowledgements
The reviewer thanks Frode Weierud, John Gallehawk, and the late Ralph Erskine for their assistance in obtaining documents used in the preparation of this review.
Notes
1 Ferris defines Comint as material taken from reading messages, and Sigint as widening this to include material obtained from assessing the external features of signals.
2 Except for information already in the public domain. Ferris hints that GCHQ read much postwar diplomatic traffic, for example during the Suez crisis (though without mentioning Wright (Citation1987), 82–86), Konfrontasi with Indonesia, the Falklands campaign, and even recently.
3 For example, see Aldrich (Citation2010), Appendix 2.
4 Denniston had served in Room 40 during WWI, but not as its leader.
5 “C” was the head of SIS, and therefore already responsible to the FO.
6 The Air Section was not formed until 1935.
7 Pinches: cryptographic material obtained via clandestine methods such as burglary or espionage.
8 Ultra was a general codename for intelligence derived from breaking the highest-level Axis cryptosystems.
9 Travis received a knighthood in 1944. Denniston received a CMG in 1941, but nothing further; his reputation was further damaged by the unfair portrayal of his character in the 2014 film The Imitation Game.
10 See Travis (Citation1943).
11 See Erskine (Citation2000, Citation2003) on what was exchanged, though the former does not include some seemingly valuable items listed by Ferris. Much important information on Enigma was provided verbally.
12 Happenstance heightened these concerns: a large proportion of the earliest Venona decrypts related to Soviet espionage in Australia, thus presenting a distorted picture. (Venona is discussed later.)
13 The Director of the NSA.
14 Unfortunately, the journey to professionalism caused friction between the Trust and the volunteers who had fought to save the site. Eventually, this caused the rebuilt Colossus and bombe machines, which should be star attractions, to be relocated to the adjacent site of the National Museum of Computing.
15 Ferris does not explain how his term “cyber commons” differs from the more common “cyberspace” – perhaps he intended an allusion to the “tragedy of the commons.”
16 See Anderson (Citation2016).
17 See https://en.wikipedia.org/wiki/Investigatory_Powers_Act_2016, accessed 27 Jan 2022.
18 For example, Max Newman, Shaun Wylie, and Peter Hilton. Bill Tutte worked on graph theory, which might be considered an applied field today, but probably not in the 1940s.
19 Chief engineer of the British Tabulating Machine Company (BTM) and designer of the British bombe.
20 From the Dollis Hill research station of the General Post Office (GPO), and designer of the Colossus.
21 Respectively the female branches of the RAF and the RN. Conscription was the British term for the draft.
22 See Erskine and Freeman (Citation2003) on John Tiltman’s long and distinguished career.
23 A German diplomatic code with an unusually strong superencipherment system.
24 German army radio-teleprinter traffic enciphered using Lorenz SZ40 or SZ42 machines.
25 Modern readers studying wartime GC&CS documents, particularly reports from the mechanized cryptanalysis sections, will surely notice the sexist language used.
26 Wireless intelligence (“Y”): the detailed study of enemy wireless networks and their operation.
27 Ferris gives contradictory dates, stating that NSA had had two female Deputy DIRNSAs by 1995. On a related topic, he claims that NSA was more progressive with respect to women than any other security agency in the world, yet two female Directors-General have already led MI5, while no woman has yet headed GCHQ, MI6, or NSA, and only recently was one formally confirmed as Director of the CIA.
28 Two-part codes assign codegroups to their plaintext equivalents in random order. Thus, each correspondent requires two physical codebooks, one in codegroup order, the other in plaintext order.
29 Ferris’s numbers seem questionable, implying an average of over 600,000 intercepts per day throughout the war. Elsewhere, he states that a captured codebook (the Signalbuch der Kaiserlichen Marine) contained about 300,000 three-letter codegroups using the 40 symbols available in German morse, yet 403 = 64,000.
30 Ferris finds no evidence supporting the legend that Churchill received decrypts even when out of office.
31 Cooper led GC&CS’s Air Section.
32 A precursor to the better-known “Purple” machine. See Deavours and Kruh (Citation1985), Chapter VI, which includes photographs of an American-built device (an analog) that emulated the Red machine.
33 Implying that it was used mainly after the necessary decryption keys had been found.
34 Using Turing’s “comic strips,” a paper emulation of the Enigma, to decrypt a few letters will make the point (see Turing (Citation1939–1942), Chapter I).
35 See Bouchaudy (Citation2021). By then, the French had shared critical information with GC&CS: instructions for using the machine, a long message with its ciphertext and key, and a wiring diagram showing how the plugboard worked.
36 See Kozaczuk (Citation1979), Appendix D, p. 251.
37 TNA HW 14/22 shows Denniston’s tact and firmness when dealing with Knox.
38 The late Mavis Batey showed this reviewer a set of rods, probably made after the war, that were about 15 inches long. See also Batey (Citation2009), Appendix 2, and Turing (Citation1939–1942), Chapter II.
39 See Hinsley and Stripp (Citation1994), Chapter 16, and Kozaczuk (Citation1979), Appendix D, p. 257. Once given this permutation, Peter Twinn took just two hours to recover the wiring of two Enigma rotors, using Knox’s methods.
40 See Erskine (Citation2006) and references therein.
41 Ferris may have relied on Rejewski, quoted in Kozaczuk (Citation1979, 60): “I don’t know how Knox’s method was supposed to work, most likely he had hoped to vanquish Enigma with the batons.”
42 See Erskine (Citation2006) and references therein.
43 Delivered in November 1938, the Bomba became obsolete in January 1939 when German keys began to include more plugboard connections, even before the indicating system was changed.
44 The first bombe, Victory, was delivered without DBs. Fortunately, they were easily added to Keen’s design. See TNA HW 25/19 and Welchman (Citation1982), Chapter 4.
45 See, for example, Herivel (Citation2008, 123–4).
46 See Mahon (Citation1945) and Alexander (Citation1945). Hut 8 was responsible for cryptanalysis of naval Enigma.
47 The three-rotor naval Enigma allowed 336 rotor orders; Ferris states (incorrectly) that the four-rotor naval machine (M4) increased this number to 8736 (336 x 26). Initially, it remained unchanged at 336; later deployments increased it to 1344 (336 x 4). See Erskine and Weierud (Citation1987).
48 Cribs: stretches of ciphertext whose corresponding plaintext was known or guessed. Ferris’s definition is broader: “anything which suggested the content of messages.”
49 Menus could be constructed from this evidence, but running them stressed the bombes.
50 An overlap (equivalently, a depth) occurs when portions of multiple messages are enciphered using the same stretch of key. The concept applies both to codebook systems and to cipher machines.
51 The sheets were printed in the town of Banbury. See Hosgood (Citation2007) and Alexander (Citation1945) for more detail.
52 Ferris cites Kahn (Citation1991), who makes this clear. By August 1940, BP knew the wiring of all eight naval rotors from the Poles and early wartime captures. The wiring of M4’s new rotors and reflectors was recovered cryptanalytically.
53 See Weierud (Citation2000) or Copeland and others (2006), Chapter 25.
54 See Reeds, Diffie, and Field (Citation2015), or Copeland and others (2006), for descriptions of the Lorenz SZ40/42.
55 See Hinsley and Stripp (Citation1994), Chapter 19.
56 See Tutte (Citation1998), and Copeland and others (2006), Appendix 4. To “set” a wheel was to find its starting position for a given message.
57 WWII teleprinters used the Baudot alphabet, which encoded each letter into 5 binary impulses. The SZ42’s “chi” key wheels generated a stream of pseudo-random letters used in the first stage of encryption.
58 The “Heath Robinson” mentioned by Ferris was just one of several design iterations.
59 See the Testery report (TNA HW 25/28), released 18 years after the Newmanry report (HW 25/5).
60 From late 1944, the Testery received some mechanized help in psi- and motor-wheel setting from the relay-based “Dragon” machines. See Hinsley and Stripp (Citation1994), and Reeds, Diffie, and Field (Citation2015).
61 For example: 17 sets of wheel-patterns were recovered during the week ending November 12th, 1944. Six were obtained from depths and one from a crib; the remainder came from “rectangling” on Colossus. See Small (Citation1944).
62 Desch designed the US Navy’s version of the bombe. Per Ferris, by 1943 NCR “produced a better bombe even than the final version, after viewing BTM’s system and receiving advice from Turing.” Desch never saw a BTM bombe during WWII, but likely examined drawings and photographs. Ferris’s claim of superiority is also debatable: NCR’s machine ran faster, but BTM’s was more flexible and ran multiple menus simultaneously; their effective throughput was similar. Desch’s design was innovative and began operation at a crucial time; it delivered excellent service against both 4-wheel and 3-wheel Enigma traffic.
63 In other words, the Newmanry was founded on Turing’s discovery. See Reeds, Diffie, and Field (Citation2015, 298). To “difference at one” was to subtract each letter of an input stream from its successor.
64 See also Ferris (Citation2005), Chapter 4.
65 The stencil was a grille laid over the pages of an additive table, prolonging its useful life by providing a pseudo-random selection of additive groups. Britain could have deployed it much earlier.
66 Both machines, as deployed, featured complex stepping patterns and far more rotor orders than was possible with Enigma. Later models of Typex also featured a pluggable reflector.
67 See, for example, In/7 War Diaries (Citation1941). In/7/VI, from 1940 to 1942 the Sigint organization of the German army’s high command (OKH), stopped work on Typex at the end of 1941, concluding that it was pointless when the rotor wirings were unknown. By then it had studied both traffic and captured machines (though without their rotors), and accurately determined Typex’s basic operating principles. The reviewer thanks Frode Weierud for this reference and an accompanying translation.
68 See Ferris (Citation2005), Chapter 5.
69 Rommel’s experienced Sigint unit under Capt. Alfred Seebohm was captured, and leaks via Bonner Fellers, the US military attaché in Egypt, were closed. Ferris also notes that British deception of the Abwehr began during the desert campaign, but says this resulted from the solution of its codebooks, rather than of its hand ciphers, as was the case.
70 The Beobachtungsdienst (B-Dienst) was the Sigint arm of the German navy.
71 See Donini and Buonafalce (Citation1990).
72 See Marks (Citation2001). The pluggable reflector was a major threat to BP’s grip on Enigma traffic.
73 See Welchman (Citation1982), Chapter 7.
74 See Gardner (Citation1999).
75 Ferris does not say so, but Hitler may have been more fixated than his generals, which was all that was needed.
76 Also known as the “Water Transport Code,” or “2468.” Sources differ on who first broke into this code.
77 See Hinsley (Citation1996).
78 Elint: intelligence derived from electronic emissions such as radar and telemetry.
79 See Budiansky (Citation2016, 300); Aldrich (Citation2010, 377); and Aid (Citation2009, 164). Authors differ on whether this success was compromised by GCHQ’s Geoffrey Prime or NSA’s Ronald Pelton.
80 See Budiansky (Citation2016, 182). ERA’s Atlas (delivered in 1950) was used to search for repeated use of keys in Russian one-time pad traffic. When GCHQ’s Oedipus joined the effort in 1954, it identified further examples from the mid-1940s. For more on Oedipus, see Lavington (Citation2006) and Aldrich (Citation2010, 349).
81 Some historians have concluded that Able Archer was so realistic that some Soviet leaders thought a NATO nuclear strike was imminent. See Wikipedia: “Exercise Able Archer” and references therein: https://en.wikipedia.org/wiki/Exercise_Able_Archer (accessed April 3rd, 2022).
82 See Aldrich (Citation2021).
83 See Aldrich (Citation2021) and Volmers (Citation2020).
84 Though the date of Rommel’s assessment before his Gazala offensive is given as May 1941, rather than May 1942. We should not find both “Zimmermann” and “Zimmerman,” or “Keen” and “Keene,” in close proximity in the text. Nor should “Herivel” be given as “Herrival,” or “Rowlett” as “Rowland.”
85 In the printed edition. Electronic versions allow the images to be displayed at more usable sizes.
86 For example, see Bouchaudy (Citation2021).
87 See Rejewski (Citation1982) on Hinsley et al. (Citation1979), Appendix 1. See also Welchman (Citation1986) on Kozaczuk (Citation1979).
88 The first major disclosure, in English, of the breaking of Enigma. See Winterbotham (Citation1974).
89 See West (Citation1986), Welchman (Citation1982), and Greenberg (Citation2014).
90 See Miller (Citation2020) and Dymydiuk (Citation2020). Dymydiuk discusses disclosures from 1995, analyzing why the operation nevertheless continued to be effective. On a separate story of “breakable” machines, Ferris flatly denies the legend that Britain sold surplus Enigma machines to developing countries after WWII.
91 See Aldrich (Citation2010, 312–9).
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Philip Marks
Philip Marks has been studying the history of WWII-era cryptography since 1974 and is currently a member of the editorial board of Cryptologia. His main research interest is in computer simulation of the cryptanalytical methods and machines used by the British and American signals intelligence agencies of that period.