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

Table 4.4
Key 3 1 5 2 4
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
26 27 28 29 30
31 32 33 34 35
and if we look at the intervals between the underlined numbers we find
that
and
1 and 2 are 14 places apart
2 and 3 are 28 places apart
3 and 4 are 21 places apart
4 and 5 are 14 places apart
i.e. the underlined numbers fall at intervals of multiples of 7, so that
when we arrange the ‘text’ in 7 rows of 5 they fall into the same row.
If however we take this ‘cipher’ text and apply the transposition again
(Table 4.5)
Table 4.5
Key 3 1 5 2 4
the ‘cipher’ text is
2 7 12 17 22
27 32 4 9 14
19 24 29 34 1
6 11 16 21 26
31 5 10 15 20
25 30 35 3 8
13 18 23 28 33
Jigsaw ciphers 45
7 32 24 11 5 30 18 17 9 34 21 15 3 28 2 27 19 6 31 25
13 22 14 1 26 20 8 33 12 4 29 16 10 35 23
and we see that pairs which were originally adjacent in the ‘plaintext’ are
now non-uniformly distributed in the ‘cipher’ text,