1. Prof. Neeraj Bhargava
Mrs. Shubha Chaturvedi
Department of Computer Science, School of Engineering & System
Sciences
MDS University Ajmer, Rajasthan
2. It is also known as Multiple groups substitution.
It involves replacing a one group of character in the
plaintext message with another groups of character in
cipher text.
In a Polygraphic Substitution cipher, plaintext letters are
substituted in larger groups, instead of substituting
letters individually.
Here the plaintext is divided into groups of adjacent
letters of the same fixed length and than each such
group is transformed into a different group of same
length letters in cipher text.
n playfair cipher unlike traditional cipher we encrypt a
pair of alphabets(digraphs) instead of a single alphabet.
4. Hill cipher is a polygraphic substitution cipher based on
linear algebra.
Each letter is represented by a number modulo 26. Often
the simple scheme A = 0, B = 1, …, Z = 25 is used, but
this is not an essential feature of the cipher.
To encrypt a message, each block of n letters (considered
as an n-component vector) is multiplied by an invertible n
× n matrix, against modulus 26.
To decrypt the message, each block is multiplied by the
inverse of the matrix used for encryption.
The matrix used for encryption is the cipher key, and it
should be chosen randomly from the set of invertible n ×
n matrices (modulo 26).
5. The hill cipher formula can be expressed in
terms of columns ,vectors and matrics.
Encryption =c=(k*p) mod 26
Decryption=p=(k*c)mod 26
6.
7. We have to encrypt the message ‘ACT’ (n=3).The key is ‘GYBNQKURP’ which
can be written as the nxn matrix:
8. To decrypt the message, we turn the ciphertext back into a vector, then
simply multiply by the inverse matrix of the key matrix (IFKVIVVMI in
letters).The inverse of the matrix used in the previous example is:
9. Given Plaintext is = “DOG”
Step1-Put DOG in a matrix from according to
numbers. D= 3
O= 14
G= 6
Choose a random key according to the size of
plain text. Random key is 3*3
3 6 24 1
14 13 16 10
6 20 17 5