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

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solutions to problems
Table S.3
A B C D E
A A B S O L
B U T E C D
C F G H I K
D M N P Q R
E V W X Y Z
We begin the decryption by converting the monographs back into
digraphs:
BDCAC DCBAC CAAEB BABBD ECCEB CBCAA BCABC
CBBAB CBAEB EDCCD.
Table S.4
3 1 5 2 4
E B C C B
C D B A C
C C A A A
E A E E B
B C B B C
C D E B C
B C D A B
C B C B B
A A C B A
A C D D B
The transposition is 3-1-5-2-4 so we write this text vertically into a rectangle
with five columns in the column order given by the transposition: see
Table S.4. Finally we recover the plaintext by reading the text row by row
and converting the digraphs back to monographs using the 5�5 square
which produces the text
WHENSHALLWETHREEMEETAGAIN
or, inserting spaces,
WHEN SHALL WE THREE MEET AGAIN
– the opening line of Shakespeare’s Macbeth.
5.2 (Playfair)
With the keyword RHAPSODY the Playfair encipherment square is as
shown in Table S.5