This document discusses product ciphers, which combine substitution and transposition ciphers for stronger encryption. It provides an example of encrypting the plaintext "COMPUTER" using a two-step product cipher. First, substitution encryption is done using a 6x6 matrix. Then, transposition encryption is performed by rearranging the ciphertext columns according to a keyword. The document explains how to encrypt another plaintext "CRYPTOGRAPHY" using the same technique with a different keyword.

1. Prof. Neeraj Bhargava
Mrs. Shubha Chaturvedi
Department of Computer Science, School of Engineering
& System Sciences
MDS University Ajmer, Rajasthan

2. It is product cipher is a combination of substitution
and Transposition cipher.
Product cipher, data encryption scheme in which
the ciphertext produced by encrypting a plaintext
document is subjected to further encryption.
By combining two or more simple transposition
ciphers or substitution ciphers, a more secure
encryption may result.

3.  One of the most famous field ciphers of all time
was a fractionation system, the ADFGVX
cipher employed by the German army
during World War I.
 This system used a 6 × 6 matrix to substitution-
encrypt the 26 letters and 10 digits into pairs of the
symbols A, D, F, G, V, and X.

4.  Step-1
Substitution by modified polybius A D F G V X matrix.
A D F G V X
A
D
F
G
V
X
L E M O N A
B C D F G H
I J K P Q R
S T U V W X
Y Z 0 1 2 3
4 5 6 7 8 9

5. Plain text ->
C O M P U T E R
Intermediate cipher text ->
DD AG AF FG GF GD AD FX
In the above step draw 6*6 matrix , and fill the grid
with the random combination of 26 letters of the
alphabets and then 10 digits .( 0 TO 9).
STEP-2
Transposition by single columinar method . Apply
the single columinar transposition to the above
intermediate cipher text by using the second
Keyword ->
BREAD

6. Use matrix according to the length of key.
B R E A D
Intermediate
Cipher text
D D A G A
F F G G F
G D A D F
X

7. Now Re-arrange the columns in the ascending order.
A B D E R
Plain text -> COMPUTER
Cipher text ->
G D A A D
G F F G A
D G F A D

8. Find out the A D F G V X cipher for the :
Plain text -> ” CRYPTOGRAPHY“
Key -> “ATTACK”