Form a square by writing the letters down in rows of 5.
Fill in the remaining square with unused letters in order
Example: Keyword Edinboro -> edinbor
e
d
i/j
n
b
o
r
a
c
f
g
h
k
l
m
p
q
s
t
u
v
w
x
y
z
Rules for encryption/decryption
Take the plaintext and split it into letter pairs
If a pair contains the same letter insert an x
If the last letter is not paired, add an x.
Find the letters in the table
If they are in the same row, shift each letter to the right by one, wrapping to the right if necessary
If they are in the same column, shift each letter down by one, wrapping to the top if necessary
Otherwise the letters form a square. Find the alternative corners of the square and use the letter on the same row for substation.
Example plaintext: the attack is at dawn
Letter Pairs: th ea tt ac ki sa td aw n
Split Duplicates: th ea tx ta ck is at da wn
th -> ql
ea -> io
tx -> sy
ta -> sc
ck -> al
is -> ax
at -> cs
da -> ir
wn -> yd
ciphertext qliosyscalaxcsiryd
How would you decode?
Encrypt "Send More Monkeys" with the keyword "Fun Times"