Another type of transposition cipher uses a keyword. First choose a
keyword where each letter is unique; in this example we'll use
PRIVATE, which we'll use to encode the riddle:
Feed me and I live, give me a drink and I die.
Arrange the letters of your message as a block underneath the keyword,
filling in the block with dummy letters as needed:
P R I V A T E
F E E D M E A
N D I L I V E
G I V E M E A
D R I N K A N
D I D I E D U
Next, number the letters of the keyword in the order that they appear in
the
alphabet. A is 1, E is 2... and so on:
4 5 3 7 1 6 2
P R I V A T E
Then
re-arrange each column of letters so that they fall in
numerical
order:
1 2 3 4 5 6 7
A E I P R T V
M A E F E E D
I E I N D V L
M A V G I E E
K N I D R A N
E U D D I D I
The
ciphertext in this case can be arranged however you want, and
whoever knows the
keyword can reverse the process and
decipher it
fairly easily:
MAEFE EDIE INDVL MAV GIE EKNI DRANE UD DIDI