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

84
chapter 7
We now turn our attention to the two remaining places where it looks
as if THEX might be in one of the texts, namely at positions 39 and 41.
These are obviously incompatible, since they overlap, so at most one of
them is right. There is a bit more evidence available since if THEX is
present it should be preceded by the separator, X. We accordingly decrypt
X at positions 38 and 40 where the cipher letters are X and L which give A
and O as the corresponding plaintext letters and so yield the possible
plaintext pentagraphs
ABEEO at position 38
OPENH at position 40
The first of these doesn’t look likely; the second looks better and since
a meeting is being mentioned it is quite possible that a place is named.
Even without collateral information, since COPENHAGEN fits the pentagraph
it is worth trying. We therefore try C at position 39 and A, G, E, N
and X in positions 45, 46, 47, 48 and 49 which produces the following
texts for positions 39 to 49:
Cipher ULILREJATVQ
Text1 S THE JUPIT
Text2 COPENHAGEN
This is very convincing and gives us an extra piece of useful information,
for The Jupiter is the name of Mozart’s last symphony and we might
therefore expect his name to occur in Text 1, somewhere between positions
19 and 38. Furthermore, the word COPENHAGEN should be preceded
by a separator and so, putting in the cipher letter, X, and the text
letter, which is also X in this case, we obtain A at position 38 of Text 1
which therefore reads
Text1 .AS THE JUPITE
Since we are dealing with Mozart’s last symphony the letter in position
37 might well be W and that at 36 would then be X. Substituting these
into the cipher we obtain, for positions 36 to 49,
Cipher FJXULILREJATVQ
Text1 WAS THE JUPIT
Text2 IN COPENHAGEN
There is a 50th cipher letter, B, which ought to give E in TEXT1 and
‘space’ in TEXT2, and this is the case, adding further confirmation, if