Uniliteral Polyalphabetic Substitution Ciphers
Multiliteral Polyalphabetic Substitution Ciphers
Monographic Polyalphabetic Substitution Ciphers
Polygraphic Polyalphabetic Substitution Ciphers
Polyalphabetic substitution ciphers use two or more cipher
cipher, the identity of each clear unit is changed [while its position is
retained] but the identity of each clear unit is changed over time. This
is a new dimension in the complexity of the encryption scheme. By using multiple
cipher alphabets, the clear symbol "T" can encrypt to "X" at one point in the
cipher text, "P" at another point, and so on.
confusing, but this system is accomplished via a key.
[with only two alphabets, no real key is required, so we simply alternate be
tween the two cipher alphabets when encrypting].
Clear Alphabet

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

Cipher Alphabet #1

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

Cipher Alphabet #2

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

then repeating this process
[the encrypted message is]: U J J U J U B U F E S G U O F U T C H G
[original message for comparison]: T H I S I S A S E C R E T M E S S A G E
likely with a short key  in this case the key length is 2]. "I" has the same
result. "S" is encrypted as "U" four times but encrypted to "T" once. "E" is
encrypted as "F" and "G" both twice.
the other points.
quencies of the underlying clear message. Not only that, the patterns of the
words are no longer the same. "T H I S" is a word with no redundancy [repetitive
letters] whereas the cipher word representing it, "U J J U", appears to have two
repretitive letters.
alphabets [where N is the key length]. In this case, the length is two, so you
would perform a frequency analysis [starting with the first letter] on every
other letter [encrypted by the first cipher alphabet] and then frequency
analysis [starting with the second letter] on every other letter [encrypted by
the second cipher alphabet]. In this case, because the message is so short, a
frequency analysis or IOC would not be very helpful.