Evening star., 1951-06-24
Todoys Mechonized Codes Have Old Time Rivals
But Modern Ones
Are Nearly Proof
Against Betrayal
By Hermon R. Allen

By Herman R. Allen
When two young officials of the
British Foreign Office disappeared
recently, the question was raised
in Parliament whether they had
taken with them the British dip
lomatic code and might betray 1t
to the enemy In the cold war.
Actually. although 1t might be
embarrassing If files Of inter-
cepted code messages Of the past
should be translated, betrayal Of q
code means little more than an
inconvenience In setting up q new
one-assuming. that is. that you
know or suspect the old one has
been compromised.
A code is fairly easily con-
structed, but about the only way
to keep 1t secret is to guard the
key. To make q code message
more difficult to break down. the
coded words are often put into
cipher.
The main difference between
code and cipher is this:
In a code system. words stand
for other words--or for phrases or
even whole sentences. You can
make q code by scrambling the
dictionary so that dog" stands
for submarine" for example.
You can make up nonsense words,
so that "ABABC" might mean
wait for further orders" You
could use groups of figures. Or
you could draw q picture to rep
resent o word.
In q cipher system, letters or
symbols stand for letters.
Most ciphers are much more
intricate than codes. There are
two general kinds: "Transposi-
ton" ciphers, the simplest kind.
and substitution" ciphers, which
can be made extremely difficult.
A simple transposition cipher
familiar to every schoolboy-is the
reversed alphabet, in which "Z"
stands for "a" and "Y" stands
for "B." etc. This can be made
a little more complicated by
scrambling the alphabet, instead
OF simply reversing it.
Substitution Ciphers Horder
There are harder types of trans
position ciphers. But they pre-
sent no real problem to the skilled
cryptographer, as an expert in
codes and ciphers is known. Their
big defect is that it is known that
the most frequently used letters
in European languages are EFT
A-O-I-N. in that order.
Substitution ciphers are another
story.
Fundamentally almost every ci-
pher in use today is a substitution
cipher. based on something called
the Vigenere Table, named for the
Frenchman who invented it in
the 10th century.
The basic Vigenere Table is
shown in the box lower down in
the next two columns-the start
Of 1t. The table continues until
you have 26 complete alphabets,
each one set over by one letter.
To use it. you first select a
key word, Say the key word is
bad. You break your message
up into five letter units and write
the key word under it. repeating
as often as necessary. like this:
WEATT ACKAT DAWNT oMoRR
BADBA DBADB ADBAD BADBA
Then take the first letter Of your
message-"W." Find that letter in
the alphabet across the very top
OF the table Follow that column
down to the line with a "B" to
the left of it. The two meet at
"X." That's the first letter Of
your cipher message. The next
cipher letter will be e." the same
as in the original message, because
that's where the "E" column and
the "a" line meet. And SO on.
Actually no diplomat or military
man in his right mind would use
this basic table today. Any half
way competent cryptographer
could crack cipher based on it.
So all sorts of variations are used.
An obvious first step would be
to mix UP the alphabets in the
table. You could re-encipher the
message using a table of alphabets
scrambled in an entirely different
way. Or you could re-encipher it
using transposition system.
The cryptographer has many
such tricks. Sometimes he throws
In signal letters" to indicate he's
going to start using a new cipher
or key word altogether.
Cases have been known in his