Reference no: EM132282094
Q1 Cryptanalysis
(a) [Cryptanalysis on Simple Substituion Cipher]
Show step-by-step process to find the plaintext and the key for the following ciphertext using the concept of simple substitution cipher as discussed in Lecture-1:
BUJKIXQLUVKD
(b) [Cryptanalysis on Double Transposition Cipher]
Decrypt the following ciphertextusing the double transpositioncipher (as discussed in the Lecture-1 and Tute-1) using a matrix of 9 rows and 8 columns.
TAWETNSHENGAMINEQTNSUIOEFHYTUENLIUVOFHAYETCNSENEETSFRHIOOVOAUEGHENHUFDTO
(c) [Cryptanalysis on Substituion Cipher]
Assume that the following ciphertext has been produced using a substitution cipher. Please note that it may not be a simple ‘shift by n'substitution. The ciphertext is as follows:
AOEDQFTREDAENUFTREJSHGCTAJXGUTOC QD AOEAGUYDSJGFUAQJYJSQYSJGFUAQJYAJTGEVEYAJAOEGDSGJFJLDEGVQYXQADFEUYQYX. OEGE, BE TGEVEYAQYSJGFUAQJYSGJFGEUHOQYXUYEYEFCQY U KDULRESJGF. HJYSQMEYAQURQAC QD VQEBEMUDAOEHEYAGURQDDKEQYAOESQERMJSQYSJGFUAQJYTGJAEHAQJY.DEHKGEHJFFKYQHUAQJY QD AOEDAGUQXOASJGBUGMKDEJSHGCTAJXGUTOC.AOEIECFUYUXEFEYATGJLREFOUDTGEVEYAEMDEHKGEHJFFKYQHUAQJYSGJFLEHJFQYXHJFFJYTRUHE.AOEMEVERJTFEYAJSTKLRQH-IECHGCTAJXGUTOCHGEUAED U RUGXE-DHUREYEABJGIJSTEJTRE BOJ HUYHJFFKYQHUAEDEHKGERCBQAOJYEUYJAOEGEVEY QS AOECOUMYEVEGHJFFKYQHUAEMLESJGE.
Find the plaintext by frequency analysis technique as discussed in Lecture-1 and tutorial-1.
Q2 [Application of Hash Algorithm]
Assume that Alice, Bob and Trudy want to participate in an online auction to purchase an item. The idea here is that these are supposed to be sealed bids, i.e.each bidder gets one chance to submit a secret bid. In order to submit a secret bid, a bidder generates hashvalue of their bid amount using SHA-256 hash algorithm, and sends the hash value as their bid to the auctioneer. All of the bids are revealed when all of the participants send their secret bid to the auctioneer. Trudy is a smart person who is certain that Alice and Bob will both place their bids between $201 and $211. Trudy captures the following hash values of Alice and bob:
Hash value of Alice:
968076BE2E38CF897D4D6CEA3FACA9C037E1A4E3B4B7744FB2533E07751BD30A
Hash value of Bob:
FC56DBC6D4652B315B86B71C8D688C1CCDEA9C5F1FD07763D2659FDE2E2FC49A
i. Describe a forward search attackstep-by-stepby which Trudy can determine Alice's and Bob's bid from their respective hash values.
ii. Describe how the above bidding procedure cane be modified to prevent a forward search attack.
Q3 [RSA Encryption algorithm]
Say, Alice and Bob are two officers in the federal security services. Alice wants to send a secret message to Bob by encrypting the secret message. In other words, Alice is the sender and Bob is the receiver. However, Alice and Bob have no shared secret key. Therefore, they have to use Public-Key cryptography. Bob generates public and private keys using RSA encryption algorithm and sends the public key to Alice. Alice encrypts her secret message using RSA encryption and sends the encrypted message to Bob. Consider that Alice has a secret message M=9876 to send to Bob. Bob uses parameter p=1931 and q=947, and chooses a small public key parameter e. What are the values of suitable public and private keys? How would Alice encrypt message M=9876? How would Bob decrypt the encrypted message C with the private key?You need to show every step. [Hints: Use the concept that is discussed in Lecture-3 and Tutorial-3].
Q4 [Breaking RSA Encryption algorithm]
Recently, researchers have successfully decrypted the RSAciphertext without knowing the private key. In this question, we would like to examine your understanding on one of the RSA cryptanalysis techniques, called prime factorization. Assume that Alice wants to send a message to Bob. Bob generates public and private keys using RSA Encryption algorithm and publishes the public key (n=4717, e=19). Alice has a secret message M to send. Nobody knows the value of M. She encrypts the message Musing the public key and sends the encrypted message C=1466to Bob. Trudy is an intruder who knows RSA and prime factorization well. She captures the encrypted message C=1466. She also has the public key (n=4717, e=19) because it is known to all. How can she decrypt the encrypted message C and find the value of M? Show all the steps.[Hints: Use the concept that is discussed in Lecture-3].
Q5 [ElGamalEncryption algorithm]
Alice has a message M=51to send to Bob securely using ElGamal encryption algorithm. Bob chooses p=8167, g=4063, x=71. Alice chooses r=29. Show the encryption and decryption steps.[Hints: Use the concept that is discussed in Lecture-4 and Tutorial-4].
Q6 [PaillierEncryption algorithm]
Alice has a message M=3456to send to Bob securely using Paillier encryption algorithm. Bob chooses p=137, q=101,and selects an integerg=173. Alice selects a random number r=73. Show the encryption and decryption steps. [Hints: Use the concept that is discussed in Lecture-4 and Tutorial-4].
Attachment:- SECURITY IN COMPUTING.rar