Enigma-Z image from the April 2004 issue of Cryptologia Magazine. It was copied from
from a [circa] 1931 'sales' brochure. (Image provided by David Hamer, NCM Foundation).
The following article (found on the web) accompanies the image.
MODEL Z: A NUMBERS-ONLY ENIGMA VERSION
Cryptologia, Apr 2004 by Arturo Quirantes
[The Figures referenced in the original article are not available at this time]
ABSTRACT: A review of pre-WWII documents in the Spanish Foreign Affairs Ministry has discovered a hitherto unknown Enigma modification, called "Model Z", capable of encrypting numbers only. This model seems to be unknown to the Enigma community. The few known details concerning Enigma Z are outlined here.
In November 10, 1931, the Spanish Ministry of State (Foreign Affairs) made a request to its Berlin embassy to report on cipher machines used in Germany. Within a week, the Chiffriermaschinen Aktiengessellschaft answered the embassy's queries with an offer for three types of machines . The first, labeled "ENIGMA Model A 27", seems to be the standard, commercial model.
The second one, Model H 29, is an eight-rotor printing cipher machine and had a price of 12,000 Reichmarks; an accompanying brochure - which includes an encrypted test letter dated 1 October 1931 - shows it to be identical to the early model in Figure IA of Kruh and Deavours . However, the biggest surprise lies in the third model offered to the Spanish Embassy: a "10-glowlamp ciphering machine". It was labeled "Model Z 30 Enigma", and had a price tag of 600 Reichsmark.
Surprisingly, I have been unable to find any information whatsoever on any Z Enigma. Considering the lack of further documentation on any "Z Enigma" model, it might be argued that it refers to an already known model. However, two brochures at the Spanish Foreign Affairs Ministry archives suggest otherwise . One is an undated instruction manual typed in badly-translated Spanish. The other is a clean, printed brochure with two photographs of a machine that, while it resembles a standard commercial model, is clearly different (See figures 1 and 2)
The most striking difference is found on the keyboard. Instead of the usual 26 keys, the Z model has only ten numerical keys, 0 to 9 (see Figure 1, number 1). The glowlamps are likewise numbered to 9. The rotor core is made up of three movable rotors plus a rotating reflector. The rotors are clearly different from the commercial standard model since they are also numbered 0 to 9; as it has only ten contacts, the rotors cores have lesser diameter. According to the brochure, it has a period of 10,000 - that is, all wheels reach their original setting after 10,000 keystrokes- thereby suggesting a non-Enigma (odometer) stepping.
Once the machine cover is opened, eight more spare lamps can be seen under the main row ( see Figure 2, number 19). A 4-volt battery powers the machine, but it can also be hooked to an external power supply. The machine's dimensions and weight compare to that of a commercial model.
Data for both models are given for the machine only, without the box (in the case of Model Z, oak).
Since Model Z has no plugboard and, according to the brochure description, seems not to have a movable ring-core structure, the key is made up of only two elements. The so-called "inner key", gives the name and order of the rotors (there is no reference to spare rotors or reflectors), and the "outer key" gives the rotor setting. A particular key might, for instance, might have the structure "III I II 5 2 8 1"
Unfortunately, no wiring information whatsoever is given. Only an example is given. Cleartext numbers 25183 91467 are encrypted as 38760 15924. No machine settings are given for the example, but it can be seen that no number is encrypted as itself. We can think (though not prove) that the Enigma Z was also a nonreciprocal machine.
The question then arises: what is this machine useful for? The first logical explanation is to provide a second layer of encryption to a codebook, a so-called superencipherment. Spanish diplomatic codebooks in the 1930s show a crude version of superencipherment in the form of either constant or time-dependent additives to a common codebook.
If Enigma machines worked as advertised, there would be no need to use a book code in the first place. But traditions die hard; a 1931 report from the Spanish ambassador in Berlin (obviously no cryptographer) states that a cipher machine is a good option, "as long as it's combined with a [book code] key system" A second use is also possible: to encrypt weather reports, usually in numerical form. Of course, one can only wonder about the demand on cipher machines for such tasks in the early 1930s.
Did the Spanish government buy any Model Z Enigma? According to surviving files, it did not. The Enigma machines (either Model Z, Commercial or even the massive eight-rotor Model A) were not considered as an option. Considering later developments in Allied breakings of Enigma machine messages, we might think Spain was lucky. Not so. The chosen option was a Kryha machine, highly regarded by that time but nevertheless much weaker; legend says that Friedman took less than three hours to solve a Kryha-encrypted message. Only during the Spanish Civil War (1936-39) and afterwards was the Enigma option seriously considered by the Franco nationalist forces. Spanish Enigma users included the military and naval attaches in Berlin and Italy, and also the Spanish volunteer Blue Division which fought alongside the German forces in the Russian theater during World War II.
REFERENCES FOR ABOVE ARTICLE
1. Spanish Foreign Affairs Ministry Archives. Documents from the Spanish Embassy in Germany: dispatches and telegrams. Reference 007459-4-R.
2. Kruh, Louis and C. A. Deavours. 2002. The commercial Enigma: Beginnings of machine cryptography. Cryptologia. 26(1): 1-16
ADDRESS: C/Torre Hidalgos 1, 1° B. 18004 Granada SPAIN. firstname.lastname@example.org.
Arturo Quirantes holds a PhD in physics and is a full-time teacher at the University of Granada (Spain). He has a nonprofessional interest in cryptology, particularly in the fields of historical cryptography and crypt analysis. He's the editor of the Boletin Enigma (Enigma Bulletin), a Spanish e-zine on the history of crypology and the defense of digital privacy, available online at http : //www.ugr.es/~aquiran/cripto/enigma.htm.
Copyright Cryptologia Apr 2004
Contributors and References:
1) Enigma-Z image provided by David Hamer (NCM Foundation)
2) Enigma-Z article by Arturo Quirantes - http://www.findarticles.com/p/articles/mi_qa3926/is_200404/ai_n9373517