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(a) 2 points List and briefly define categories of passive and active security attacks. Total for Question 1: 2 2. Classic Encryption (a) 1 points What are the two basic functions used in encryption a

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(a) 2 points List and briefly define categories of passive and active security attacks.
Total for Question 1: 2
2. Classic Encryption
(a) 1 points What are the two basic functions used in encryption algorithms?
(b) 1 points What are the two general approaches to attacking a cipher?
(c) 2 points List and briefly define types of cryptanalytic attacks based on what is known to the
attacker.
(d) 2 points What are two problems with the one-time pad?
(e) 2 points Calculate the determinant mod 26 of 
20 2
5 4
.
(...

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Question Preview:

(a) 2 points List and briefly define categories of passive and active security attacks.
Total for Question 1: 2
2. Classic Encryption
(a) 1 points What are the two basic functions used in encryption algorithms?
(b) 1 points What are the two general approaches to attacking a cipher?
(c) 2 points List and briefly define types of cryptanalytic attacks based on what is known to the
attacker.
(d) 2 points What are two problems with the one-time pad?
(e) 2 points Calculate the determinant mod 26 of 
20 2
5 4
.
(f) 3 points Encrypt the message “meet me” using the Hill cipher with the key 
9 4
5 7
. Show your
calculations and the result.
(g) 3 points Show the calculations for the corresponding decryption of the ciphertext in above part
to recover the original plaintext.
(h) 2 points Using the Vigenere cipher, encrypt the word “explanation” using the key “leg”.
(i) 5 points The following ciphertext was generated using a simple substitution algorithm. Given that
the plaintext is in English language, can you decrypt this message by exploiting the characteristics
of English Language (eg, alphabet e is the most recurring in plain text).
53305))6*;4826)4.)4);806*;48860))85;;]8*;:*883 (88)5*;46(;88*96*?;8)*(;485);5*2:*(;4956*2(5*4)88*
;4069285);)68)4;1(9;48081;8:81;4885;4)485528806*81 (9;48;(88;4(?34;48)4;161;:188;?;
Total for Question 2: 21
3. One Time Pad This problem explores the use of a one-time pad version of the Vigenre cipher. In this
scheme, the key is a stream of random numbers between 0 and 26. For example, if the key is 3 19 5
· · · , then the first letter of plaintext is encrypted with a shift of 3 letters, the second with a shift of 19
letters, the third with a shift of 5 letters, and so on.
(a) 3 points Encrypt the plaintext “sendmoremoney” with the key stream
9 0 1 7 23 15 21 14 11 11 2 8 9
(b) 3 points Using the ciphertext produced in part (a), find a key so that the cipher text decrypts
to the plaintext “cashnotneeded”.
Total for Question 3: 6
4. Block Ciphers
(a) 3 points Which parameters and design choices determine the actual algorithm of a Feistel cipher?
Total for Question 4: 3
5. AES
(a) 2 points What is the difference between Rijndael and AES?
(b) 1 point What is the purpose of the State array?
(c) 1 point Briefly describe the key expansion algorithm.
6. Given the plaintext 000102030405060708090A0B0C0D0E0F and the key 01010101010101010101010101010101.
Page 2 of 4
(a) 2 points Show the original contents of State, displayed as a 4 × 4 matrix.
(b) 2 points Show the value of State after initial AddRoundKey.
(c) 2 points Show the value of State after SubBytes.
(d) 2 points Show the value of State after ShiftRows.
(e) 2 points Show the value of State after MixColumns.
Total for Question 6: 10
7. Public Key Encryption
(a) 3 points What are three broad categories of applications of public-key cryptosystems?
(b) 3 points What requirements must a public-key cryptosystems fulfill to be a secure algorithm?
(c) 2 points What is a trap-door one-way function?
(d) 3 points Perform encryption using the RSA algorithm, as in Figure 9.5, for the following parameters:
c.
p = 7; q = 11, e = 17; M = 8
(e) 3 points Perform decryption using the RSA algorithm, as in Figure 9.5, for the following:
p = 17; q = 31, e = 7; C = 128
(f) 3 points Perform decryption using the RSA algorithm, as in Figure 9.5, for the following:
p = 11; q = 13, e = 11; C = 106
(g) 3 points In a public-key system using RSA, you intercept the ciphertext C = 10 sent to a user
whose public key is e = 5, n = 35. What is the plaintext M?
(h) 4 points In a RSA cryptosystem, the public key of Alice is e = 47, n = 4757. Find the private
key of Alice. Hint: First use trial-and-error to determine p and q; then use the extended Euclidean
algorithm to find the multiplication inverse of 47 modulo φ(n).
Total for Question 7: 24
8. Hash Functions
(a) 2 points What is the role of a compression function in a hash function?
Total for Question 8: 2
9. Message Authentication and Digital Signatures
(a) 2 points What two levels of functionality comprise a message authentication or digital signature
mechanism?
(b) 1 points When a combination of symmetric encryption and an error control code is used for
message authentication, in what order must the two functions be performed?
(c) 2 points What is the difference between a message authentication code and a one-way hash
function?
(d) 1 points Is it necessary to recover the secret key in order to attack a MAC algorithm?
(e) 2 points What requirements should a digital signature scheme satisfy?

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Solution preview

Passive attacks
Release of message contents: An Eavesdropper can listen and read the shared data between two parties.  

Traffic Analysis: The attackers or eavesdropper involves to analysis the packets which is are sent between sender and receiver. Attackers can sniff the passwords within packets.

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