Page 130 - The Secret War in the Italian front in WWI (1915-1918)

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

not exist exclusively in the military domain, has been an issue for cryptologists for decades, until
the implementation of public-key systems.

6.6 STEGANOGRAPHY: A SPY’S INSTRUMENT

TechnIcal sTeganograPhy

During the WWI, agents operating beyond enemy lines, in order to convey the information
gathered to their contact persons, were often forced to use classic communication means such as
mail, public telegraphs, carrier pigeons, advertisements on newspapers, etc., and hence tried to
conceal their dispatches by steganography.
The term steganography comes from Greek and means hidden writing. It comprises systems
hiding the very existence of the message by technical or linguistic methods .
34
Invisible inks are among the most notorious technical steganography methods. In order to hinder
the detection of these apparently invisible writings, chemical laboratories - in particular German
ones - designed more and more sophisticated inks, constantly challenging the Entente’s specialists
who, in the meanwhile, were trying to identify the chemical substances that could reveal the
writings hidden by the new inks . The Italian Intelligence Service also achieved a valuable
35
level of specialization in the field, progressing from “the first basic means to finding out secret
correspondence […] to well-equipped chemical laboratories where it was almost impossible for
any sophisticated substance used to hide suspect correspondence to go undetected” .
36
Several other technical steganography methods, also used after the WWI, allowed for instance
photographically reducing an image to the size of a full stop in a typewritten document. More
recently, messages were hidden inside images transmitted via Internet.
Unlike technical steganography, linguistic or textual steganography aim to hide a secret text inside
an apparently harmless text that eventually can get through the most accurate checks, even by
censorship . The linguistic methods comprise the concealed ciphers and the concealed languages
37
(Jargon codes or language convenu).

concealed cIPhers
During the conflict, in addition to many classic versions of veiled secrete writing, such as acrostics,
grilles , etc., some numerical techniques strictly connected to cryptography were sometime
38
applied.
For instance, the number of vowels or consonants in each word of the plaintext can form code
groups: an even number can represent a 1 and an odd number represents a 0. Therefore, with
five consecutive words one can obtain five binary figures (1 to 0), generating 32 (2 ) possible
5
combinations, each corresponding to a letter of the alphabet or to a number, or to a symbol of the

34 The term was introduced by Abbot Trithemius (Johann von Heidenberg from Trittenheim), who entitled his book
“Steganographia”, first published in 1506.
35 The evolution of the technique and use of invisible inks during WWI is described in H.O. Yardley, op. cit., p. 55-89.
36 O. Marchetti: op. cit., p. 92.
37 Textual steganography introduced by Abbot Trithemius is still applied today to digital texts.
38 The initial letters of the words of an acrostic are used to make up the hidden message. Cardano’s grilles are made by holes
in a metal plate or on a sheet of paper. The message is written into the holes; a support text completes the message.

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