TheCodeBreakers
The simplest tableau is one that uses the normal alphabet in various
positions as the cipher alphabets. Each cipher alphabet produces, in
other words, a Caesar substitution.
This is precisely Trithemius' tableau, which he called his "tabula
recta." Its first and last few lines were:
abcdefghiklmnopqrstuxyzw
bcdefghiklmnopqrstuxyzwa
cdefghiklmnopqrstuxyzwab
defghiklmnopqrstuxyzwabc
efghiklmnopqrstuxyzwabcd
........................
zwabcdefghiklmnopqrstuxy
wabodefghiklmnopqrstuxyz
Trithemius used this tableau for his polyalphabetic encipherment, and in
the simplest manner possible. He enciphered the first letter with the first
alphabet, the second with the second, and so on. (He gave no separate
plaintext alphabet, but the normal alphabet at the top can serve.) Thus a
plaintext beginning Hunc caveto virum . . . became HXPF GFBMCZ FUEiB. ...
In this particular message, he switched to another alphabet after 24