Cryptology - Unofficial St. Mary's College of California Web Site

10.3. TURNING GRILLES 191
1 2 3 7 4 1
4 5 6 8 5 2
7 8 9 9 6 3
3 6 9 9 8 7
2 5 8 6 5 4
1 4 7 3 2 1
Figure 10.1: A 3 × 3 turning grille.
cut out boxes in the new sheet that are where and of the same size as the boxes
you highlighted on the first sheet. We have made a turning grille. In Figure
10.1 a set of numbers has been chosen, as the bold typeface indicates.
To encipher the message lay your grille onto a clean sheet of paper. Moving
from left to right and top to bottom, as usual, write your text in the holes in the
grille. Once you have filled the holes give your grill a quarter turn and continue
with your message. If your message is quite long you may have to repeat the
filling process on a second or even third sheet of paper, while if your message is
short, you’ll probably want to fill the remaining spots with nulls.
The deciphering process is the natural opposite of the enciphering: lay the
grill over the sheet and copy the letters off that you can see, turning the ciphersheet
one quarter each time you have copied down all the letters.
Examples:
(1) Encipher Girolomo Cardano was a mathematician using the grille in
Figure 10.1.
Nine letters at a time will be entered.
partial ciphertext looks like
After the first nine letters, the
O
I
O
R
M
G
L
O
C
Now give the grill one quarter twist and enter nine more. This make
A G
R I D
R A O
N L O
O W M
S O A C