Page 190 - The Secret War in the Italian front in WWI (1915-1918)

THE SECRET WAR ON THE ITALIAN FRONT IN WWI (1915 – 1918)

In the last part of the letter mentioned above, the Intelligence Office also conveyed a general
warning as to Service cipher use for radio dispatches containing confidential information, with
reference to a new chipher based on groups of letters distributed in the early days of the month.

The servIce cIPhers of The “c” serIes
Having lost all the certaities it had shown off in August of the previous year regarding the safety of
figure-based service ciphers, the Telegraphic Inspectorate decided to replace it with a cipher based
on groups of letters, marked by the first letter C. The first cipher of the family, called C1 , followed
23
that based on groups of letters, unknown to the Austrians and reserved since the early months of
war for particularly confidential correspondence of the Higher Commands radio stations.
During the early days of March 1916, “the mobile 0.3, 0.5, 1.5, 3 kW radiotelegraphic stations
and the fixed stations of Udine, Treviso, Osoppo, Pieve di Cadore, Arsiè, Arsiero, Verona, Brescia,
Milan received a numbered copy of a new service cipher based on groups of letters. […] which
will start being used at 5 am of next 1 April” .
24
st
As the following ciphers of the C group, the C1 was based on the replacement of letters, figures and
words with code words formed by letters of a 17-letter Italian alphabet reduced by the exclusion of
E, J, K, M, T, U, W, X, and Y. The C1 structure was analogous to that of the figure cipher because
it employed two tables, a main table and an auxiliary one, which allowed code groups of two or
three letters to be generated. As for the previous numerical cipher, in cryptograms the code groups
were grouped, to form sets with the number of letters varying from 2 to 6, facilitating the discovery
of the cipher type .
25
In his memoirs, Figl describes the breaking process of C1: the reconstruction of first line of the
main table needed only a few days while the sub-rows required more time . The main reason
26
behind the Austrian success was the strong similarity with the previous number-based cipher and
particularly the regularity shared by both, as it clearly results from the analysis of C1 tables shown
in Annex A.
The circular radio transmission, every Saturday morning, of the key repeated three times - which
is why the cipher was called ‘weekly’ - by the station in Treviso and using the previous key, shows
the cryptographic inexperience of the STM Inspectorate. Therefore, replacing the numbers with
letters did not produce any significant progress in terms of security of the Service Cipher.
During 1916, trying to escape enemy decryption, the ciphers of C series underwent numerous
changes. In mid-June during the Strafexpedition, a new cipher called CF was introduced in the 1
st
Army, adopting a dictionary formal structure. As shown in Annex A, the representations by table or
as a code are equivalent: the CF dictionary, including 17 pages, each with 17 lines and 6 columns,
corresponds to a main table of 17 lines and an equal number of columns plus an auxiliary table of
6 lines. The CF code groups containing three letters were grouped in couples in the body of the
cryptograms and the key word changed every day .
27
For fear that the previous versions might have fallen in enemy hands, on 20 August, nearly at
the end of the battle that led to the conquest of Gorizia, the C2 came into force, for coding

1
23 The acronym C initially identified the new cipher and was later changed into C1. In this book only C1, C2, etc. terms will
be used.
24 Chief Inspector of the STM, Military Journal, Service Order no. 39 of 8 March 1916 AUSSME, Series B1,105 S, Vol.88.
25 ibidem, Chief Inspector of the STM, Military Journal, Service Order no. 46, 5 July1916.
26 O.J. Horak, Oberst a.D. Andreas Figl, op. cit., p 133 and ff.
27 O. J. Horak, Andreas Figl Leben und Werk, op. cit., p.160. The adoption of the CF is not reported in the service orders of
the Chief Inspector of the STM, probably because it concerned the 1 Army only.
st

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