Code and ciphers: Julius Caesar, the Enigma and the internet

24
chapter 2
help or a hindrance to the cryptanalyst. In one extreme case a novel was
written which in over 50 000 words never used the letter E, but this was
done deliberately; the author having tied down the E on his typewriter so
that it couldn’t be used. This is a remarkable feat; here, as a sample, is one
sentence from the book:
Upon this basis I am going to show you how a bunch of bright young
folks did find a champion; a man with boys and girls of his own; a man
of so dominating and happy individuality that Youth is drawn to him
as is a fly to a sugar bowl. [2.3]
Even when shown a much longer extract from this book few people notice
anything unusual about it until they are asked to study it very carefully
and, even then, the majority fail to notice its unique feature.
Letter frequencies in languages other than English
A simple substitution cipher in any alphabetic language is solvable by the
method above: a frequency count followed by use of the language itself.
Obviously, the cryptanalyst needs to have at least a moderate knowledge
of the language, though with a simple substitution cipher he doesn’t need
to be fluent. Equally obviously the frequency count of letters in a typical
sample will vary from one language to another although the variation
between languages with a common base, such as Latin, will be less than
will be found between languages with entirely different roots. Not all languages
use 26 letters; some use fewer; Italian normally uses only 22, and
some, such as Russian, use more whilst others (Chinese) don’t have an
alphabet at all. Since the Italians normally don’t use K, W or Y these letters
are given a zero frequency, but an Italian text which includes a mention of
New York shows that even such letters may appear. In French and
German we should really distinguish between vowels with various
accents or umlauts but in order to simplify the tables below all forms of
the same letter were counted together. Thus, in French, E, É, Ê and È were
all included in the count for E. Also, numbers were excluded from the
count, unless they were spelled out, and all non-alphabetic symbols such
as space, comma, full stop, quotes, semi-colon etc. were considered as
‘other’. Upper and lower case letters were treated as the same. With these
conventions Table 2.6 shows the frequency of letters in samples of 1,000
in four European languages. The table of frequencies of letters in English
given above is repeated for convenience.