SOLUTION SET 1
B.TECH(CS) 4
TH
YEAR
CRYPTOGRAPHY & NETWORK SECURITY (ECS-084)
1. Attempt any four parts of the following:- [4x5=20] a). Give any three names of substitution techniques.
party
t
u
v
w x y
z

M
O
N
A
R
C
H
Y
B
D
E
F
G
I/J
K
L
P
Q
S
T
U
V
W
X
Z
The matrix is constructed by filling in the letters of the keyword (minus duplicates) from left to
right and from top to bottom, and then filling in the remainder of the matrix with the remaining
letters in alphabetic order. The letters I and J count as one letter. Plaintext is encrypted two
letters at a time, according to the following rules:
1.
Repeating plaintext letters that would fall in the same pair are separated with a filler
letter, such as x, so that
balloon
will be treated as
ba lx lo on
2.
Plaintext letters that would fall in the same row of matrix are each replaced with the
letter to the right, with the first element of the row circularly following the last. For example,
ar
is encrypted as
RM
.
3.
Plaintext letters that fall in the same column are each replaced by the letter beneath,
with the top element of the row circularly following the last. For example,
mu
is encrypted as
CM
.
4.
Otherwise, each plaintext letter is replaced by the letter that lies in its own row and
the column occupied by the other plaintext letter. Thus,
hs
becomes
BP
, and
ea
becomes
IM
(or
JM
, as the encipherer wishes).
As far as number of digrams is 26x26=676 is significantly greater than number of letters,
frequency analysis becomes much more difficult. For these reasons, Playfair cipher was for a

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