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

Ciphers for spies 85
that were necessary, to the decrypts obtained so far. The word IN in Text
2 should be preceded by a space, so we decrypt X at that point, position
35, where the cipher letter is Q, which produces T in Text 1. The full situation,
then, at this point is that we have decrypted positions 1 to 18
and positions 35 to 50, two-thirds of the total, and the cipher and texts
are
FLIQTNYQFKVACEHUCUACMOXRGEYYQJBNOEQFJXULILREJATVQB
THEXLASTXSYMPHONYXXXXXXXXXXXXXXXXXTXWASXTHEXJUPITE
MEETINGXISXONXTHEXXXXXXXXXXXXXXXXXXINXCOPENHAGEN
In Text 1 we are looking for the word MOZART and the T at position 35
might be the last letter of it, so we try XMOZAR at positions 29 to 34 which
give TXNOON in Text 2. The T is likely to be preceded by XA which yields
BY in TEXT1 in positions 27 and 28 and our texts now read
FLIQTNYQFKVACEHUCUACMOXRGEYYQJBNOEQFJXULILREJATVQB
THEXLASTXSYMPHONYXXXXXXXXXBYXMOZARTXWASXTHEXJUPITE
MEETINGXISXONXTHEXXXXXXXXXXATXNOONXINXCOPENHAGEN
The word BY should be preceded by X which gives (E�X)�H in Text 2
and since we would expect a date for this meeting we can reasonably try T
as the letter before H which gives (G�T)�N in position 25 in Text 1. There
are now only 6 letters to be deciphered and in TEXT2 these are almost
sure to represent a number, probably a date, which in its ordinal form
ends in TH. ELEVEN, with 6 letters, is a good candidate and subtracting
these 6 letters from the corresponding cipher letters, ACMOXR, produces
WRITTE for Text 1. The decryption is now complete and reads
FLIQTNYQFKVACEHUCUACMOXRGEYYQJBNOEQFJXULILREJATVQB
THEXLASTXSYMPHONYXWRITTENXBYXMOZARTXWASXTHEXJUPITE
MEETINGXISXONXTHEXELEVENTHXATXNOONXINXCOPENHAGEN
The cryptanalyst has not only decrypted the message he has also discovered
that the book being used as the key is probably a book either
about music or about Mozart, and this may be useful in decrypting later
messages.
This example, short and simple though it is, illustrates how the cryptanalyst
needs a combination of analytical and linguistic skills, general
knowledge, imagination and luck in order to achieve success. In addition,
do not forget that he would first of all have to realise that the message had