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INFA 640- Cryptography and Data Protection Midterm Exam Spring 2020 (Due on Tueday) 11:59 EST

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Part I (Each 4 Pts. Total 40.) Choose the best one. Please provide reason of your choice in a few sentences or reasons not choosing the other choices. Reason must be in your own words. Use guidelines for reference as given in the instructions.

1. Virus constitute all the threats to information. By protecting against virus, we keep information safe.: True/False justify your answer

2. What is not a weakness of a shift cipher?

A. Natural language letter frequency makes them easy to decode.

B. The number of letters in the alphabet makes them easy to decode.

C. Once the shift is determined the message is decoded.

D. Once you have the code book you can decode the message instantly

Reason:

3. What is the basis of the modern cryptography? _________________

A. the laws of mathematics

B. manipulation of data

C. creating disguises for information

D. none of the above

Reason:

4. A _______________ requires that the cipher alphabet changes throughout the encryption process.

a. monoalphabetic substitution cipher

b. polyalphabetic substitution cipher

c. quantum cipher

d. alphanumeric shift cipher

5. Historically, the major driving force for advances in cryptography has been __________

a. protecting business assets

b. the need for individual privacy

c. wars

d. keeping diplomatic conversations secret

Reason: _

6. one of the Network threats is

A. buffer overflow

B. slowing the computer

C. denial of service

D. computer lock up

how does it happen: _

7. Risk is __.

A. a weakness in the system

B. a circumstance that may cause loss or is possible danger

C. a vulnerability that can be exploited

D. Nothing to worry about

Reason: _

8. The trustworthiness of a system is diminished because of.

a. exposure to risks

b. high demand for keys

c. decrease in confidence

d. bad weather

Reason: _

9. The _______ controls the action of the algorithm.

a. The receiver

b. the length of the plain text

c. cipher text

d. key

Reason:

10. What has become a major web problem with respect to security?

a. scripting errors

b. mapping attacks

c. on-line surveys

d. user ignorance

Reason: _

______________________________________________________________________________Part II (6 points each, Total 30)

Q1a Complete the following Truth Table: F denotes false and T denotes true

A	B	C=A or B	D= A xor B	E= A and B
F	F
F	T
T	T
T	F

Q1b In the following Θ denotes one of the following operators: ’or’, ‘xor’ or ‘and’.

Input1 Θ input2 = Result

where, input1 and, Inpuut2 are in columns ‘A’ and ‘B’ and Results are in columns C, D, or E from the above table.

Which operation will yield? (what is Θ?)

input1 Θ result = input 2

input2 Θ result = input 1

Please show proof for one, or disprove other two

Hint:

Check

Input1 OR result = Input2?

Input2 OR result = Input1? For results C, D and E, and inputs A and B

Repeat replacing OR with AND, and XOR

As soon as the given operator is not valid for an operation go to the next operator.

Please show proof. Without proof you will get partial credit only

Q2 Using the English alphabet (i.e., mod 26 arithmetic) let plaintext = {p1, p2, pn,} and corresponding cipher text = {c1, c2, cn}.

{start A as 1, B as 2 and so on}

Suppose the encryption function is ci = pi + 7 (mod 26).

You receive the cipher text message BTBJPZ JOHUNLKAVBTNJ

What type of cipher is this?

What is the decryption function, and the decrypted/recovered plaintext, (insert spaces to make readable)?

Show all your steps.

Q3 You are Alice. You have agreed with your friend Bob that you will use the Diffie-Hellman public-key algorithm to exchange secret keys. You and Bob have agreed to use the public base g = 11 and public modulus p = 733

.

You have secretly picked the value SA = 19 You begin the session by sending Bob your calculated value of TA. Bob responds by sending you the value TB = 516.

Sb=?

What is the value of TA

What is the value of your shared secret key?

Can you guess Bob’s secret value SB and what it would be?

Show each and every step of your calculations, if you use Excel for mod calculation include the spreadsheet, for any other method include the screenshot of that method

[without the spreadsheet or screenshot, you will not get the full credit]

for mod calculation, the following identity may be useful

mod(X*Y,p) = mod[mod(X,p)*mod(Y,p),p]

mod ( X^n, p) = mod [mod(X^k, p)*mod(X^m, p), p]; where k+m=n

e.g. mod (X^17, 733) = mod [mod (X^8, 733) *mod (X^9, 733), 733]; where 8+9=17

Q4 Bob believes that he has come up with a nifty hash function. He assigns a numeric value VChar to each letter in the alphabet equal to the letter’s position in the alphabet, i.e., VA = 1, VB = 2, …, VZ = 26. For a message, he calculates the hash value H = (VChar 1 x VChar 2 x VChar 3 …x VChar N) mod (26).

Bob uses this function to send a one-word message, “PLANET” to his supervisor Bill, along with his calculated hash value for the message. Alice is able to intercept the message and generates an alternative message that has a hash value that collides with Bob’s original hash value.

Give definition and properties of the hash function.

Show a message that Alice may have used to spoof Bob’s message and demonstrate that its hash value collides with Bob’s original hash.

Q5 Consider the following plaintext message: WE HAVEN’T CONQUERED THE CORONAVIRUS.

0. (3 pts) If this message is sent unencrypted and successfully received, what is its entropy? And why?

0. (3 pts) If this message is encrypted with DES using a random 56-bit key, what is the encrypted message’s entropy? And why

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Part III

Essay Question: Length: 800- 900 words. Use APA format for in-line citations and references. (30 pts.)

Compare and contrast symmetric and asymmetric encryption algorithms.

· Your response should include a brief overview of the cryptographic basis for each type of algorithm, and a comparison of their strengths and vulnerabilities. [20 pts]

· Describe how a hacker might go about cracking a message encrypted with each type of algorithm. [6 pts]

· Suggest a specific application for each type of algorithm (symmetric and asymmetric) where the advantages clearly outweigh the disadvantages. [4 pts]

· Remember to address all points