Page 310 - The Secret War in the Italian front in WWI (1915-1918)

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

13.4 THE SWITCHING TO NEW CODES IN THE AUSTRIAN ARMY

sIgnalordung and schlüsselhefT

The replacement of the Austrian two-parts codes take place in July 1918, with a new method
reproducing a divisional system applied by the German army since January of the same year: the
so called Schlüsselheft .
44
The new system consisted of two parts: the first called Signalordung (Signalling Regulations), was
a booklet that set out the communication rules at divisional level, while the second was a one-part
code called Schlüsselheft (Encoding Booklet) with two tables for encoding and decoding, named
Geheimklappe (Secret Handkerchief).
The Schlüsselheft could be applied to radiotelegraphy as well as to telephone communications,
light signals, and geo-telegraphy . This code consisted of 38 pages including an alphabetical
45
dictionary; a list of letters, syllables, and numbers; some short standard messages to be used
in combat; a series of abbreviations and a blank list, to be drawn up by each command. There
were no traces of homophones
in any list. Such a code ensured
no secrecy and could only be
used as such only in particular
circumstances, for example for
short communications by aircraft
in flight.
Over-encoding was therefore
needed through encoding and
decoding tables (Geheimklappe).
An example of the two completed
‘handkerchiefs’ is shown in
picture 13.14 . Each combat unit
46
had to fill the 100 empty boxes
of the coding table with random 13.14 Filled encoding and decoding handkerchief (F. Sinagra' book)
numbers from 00 to 99, drawn
by lot and changed frequently
to ensure secrecy. For over-encoding, two numbers from the code groups achieved from the
Schlüsselheft were read on the first line and the first column of the encoding table and replaced
with the group found at the intersection of the corresponding column and row. The decoding table,
filled as a function of the drawing by lot, are used subsequently.
These tables allow to over-encoding only the first two digits out of the three in each code group of
the Schlüsselheft. One weak point eventually useful to enemy analysts, lied in the lack to replace
the third digit. Moreover, for as long as each version of the tables remained valid, the absence
of homophones in the code could generate code groups repetitions, useful for analysts to start
breaking the cipher. In a second edition of the cipher, four-digit code groups were used that could

44 Two-parts codes were totally compromised also when captured during war actions.
45 It also included the visual signals made by strips of cloth spread on the ground for transmitting signals to the overflying
planes.
46 The entire codebook is included in a book to be published by F. Sinagra, from which the picture has been taken.

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