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VIT AP
Introduction to Cryptography [CSE1007 - 340]
Marks: 50 Duration: 90 mins.
SECTION-A
Answer all the questions.
Alice and Bob have decided to use a Cyclic Group as an algebraic structure. Help
them to identify all the cyclic subgroups of the group G= (Z7, +) and order of all the
elements in the group.
(5)
Alice and Bob wants to communicate with each other using Additive Cipher. The
Key used for encryption and decryption purpose is K = (146)128 mod 12. Find the
value of K.
(5)
Security officer wants a secure communication with his team. For that they have
use Autokey cipher and the key k1 is the multiplicative inverse of 550 mod 1759.
Find the value of key k1.
(5)
Find all solutions of the following modular arithmetic equation with suitable
procedure:
(5)
SECTION-B
Answer all the questions.
Your Cryptography subject teacher conveys you a cipher text message
"XECNKPDYIS" using affine cipher with keys K1=11 and K2=12. Decrypt the
cipher text to find the original message.
(10)
Alice sent some secret message to Bob. Attacker EVE exist in the network and
capturing the communications, EVE succeed to know that the security algorithm in
use is a playfair cipher and key is "NETWORK". If captured ciphertext is
"FWPUEZGOGCTU" then find out actual plaintext decrypted by the EVE.
(10)
To ensure confidentiality of the message " AMARAVATI" Alice and Bob decided to
use Hill cipher. Show your calculations and the results for computing the cipher
text. Also show the calculations for the decryption of the cipher text at receiver side
to recover the original plaintext. Considered key value is given below. Note: use
filler letter as 'X' if required.
(10)
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