CPSC 433 Data Security and Encryption Techniques
Midterm Test
Multiple Choices (60%)
1.
In the OSI Security Service (X.800), which of the following is false?
a. Authentication - assurance that the communicating entity is the one claimed
b. Data Confidentiality –protection of data from unauthorized disclosure
c. Non-Repudiation - protection against denial by one of the parties in a communication
d. Access Control – restricted the access for public data or functions
e. Data Integrity - assurance that data received is as sent by an authorized entity
2.
denial of service is what kind of the attack below?
a. monitor traffic
b. obtain message contents
c. masquerade
d. passive attack
e. active attack
3.
In the model of Network Security, which of the following is wrong?
a. We need to design a suitable algorithm for the security transformation
b. We need to generate the secret information (keys) used by the algorithm
c. We need to specify a protocol enabling the principals to use the transformation and secret
information for a security service
d. develop methods to distribute and share the secret information
e. It does not need trusted third party acts as arbiter or distributor as security information.
4.
Which one of the following ciphering result of Caesar Cipher is correct? (Assume replaces each letter by
3rd letter and the plaintext is “meet me after the toga party”
a. PHHW PR DIWHU WKH WCJD SDUWB
b. PHHW PH DEWHU WKH WRJD SYUWB
c. PHHW PH DIWHU WKH WRJD SDUWB
d. PHHW PH DZWHX WKS WRJD SDUWB
e. SHHD PH DIWHU WKH WRJD SDUWB
5.
Which one below about “Cryptanalysis of Caesar Cipher” is wrong?
a. could simply try each in turn
b. we could do a brute force search
c. It only has only have 26 possible ciphers
d. If given cipher text, we could just try all shifts of letters
e. All of the above are wrong.
6.
Which one below about “Monoalphabetic Cipher” is wrong?
a. We have a total of 26! = 4 x 1026 keys
b. each plaintext letter maps to a different random ciphertext letter
c. We could shuffle (jumble) the letters arbitrarily
d. It is quite secure. No one could breaks it theoretically.
e. We could calculate letter frequencies for ciphertext to perform Cryptanalysis
7.
For the following “Monoalphabetic Cipher”, if we have
Plain: abcdefghijklmnopqrstuvwxyz
Cipher: DKVQFIBJWPESCXHTMYAUOLRGZN
Then what is the Cipher text of “ifwewishtoreplaceletters”?
a. WIRFRWAJUHYGTSDVFSFYUFYA
b. WIRFRSAJUHYFTSDVFDFUUFCA
c.
d.
e.
WIRCRWAJUHZFTDDVFSFUUFYA
WIRFRWAJUHYFTSDVFSFUUFYA
WIRABWAJUHYFTSDVDSFUUFYA
8.
Which one below about Playfair Cipher is wrong?
a. It is a 5X5 matrix of letters
b. if a pair is a repeated letter, insert a filler like 'X'
c. Does not need to use any keyword or key
d. if both letters fall in the same row, replace each with letter to right
e. if both letters fall in the same column, replace each with the letter below it
9.
Which one below about Polyalphabetic Cipher is wrong?
a. use a key to select which alphabet is used for each letter of the message
b. simplest polyalphabetic substitution cipher is the Vigenère Cipher
c. use each other alphabet in turn
d. repeat from start after certain letters in message
e. decryption simply works in reverse
10. Which one below of the “One-Time Pad” is wrong?
a. if a truly random key as long as the message is used, the cipher will be secure
b. is unbreakable since ciphertext bears no statistical relationship to the plaintext
c. can only use the key more than once
d. have problem of safe distribution of key
e. for any plaintext & any ciphertext there exists a key mapping one to other
11. Which one below about “Transposition Cipher” is wrong?
a. Transposition Cipher hide the message by rearranging the letter order
b. There is no need to alter the actual letters used
c. It is also called permutation ciphers
d. It includes Rail Fence cipher and Row Transposition Ciphers
e. It has the same frequency distribution as the original text
12. Which one below about Private Encryption and PK (Public Key) Encryption is wrong?
a. Private Encryption will use a shared key among sender and receiver
b. Public Key Encryption does need a third party to create key for communication
c. Private Encryption will also need a third party to create key for communication
d. In Public Key Encryption, anyone can encrypt using the public key, one only person can decrypt
using the private key
e. We can design a security structure so we can combine Private Encryption and PK Encryption.
13. Which statement below about Stream and Block Ciphers is wrong?
a. Stream ciphers process messages a bit or byte at a time when en/decrypting
b. Block ciphers process messages in into blocks, each of which is then en/decrypted
c. DES is one of the block ciphers that was commonly used before
d. Block ciphers would need table of 264 entries for a 32-bit block
e. Modern block ciphers involve substitution (S-Box) and permutation (P-Box) process.
14. What statement below about DES is wrong?
a. DES encrypts 64-bit data using 56-bit key
b. DES has the Permutation as the initial process (IP)
c. DES encrypts and decrypts the entire data block. No separation of the data bits needed.
d. DES has round functions to perform the permutation, S-Box mapping etc.
e. There is KEY schedule in regarding to the generation of the Keys of every round in DES
15. Which one is correct below in regarding to Confusion and Diffusion? (Choose the best answer)
a. The reason we need confusion and diffusion in cryptography is because cipher needs to
completely obscure statistical properties of original message
b. A one-time pad does this
c. Diffusion means dissipates statistical structure of plaintext over bulk of ciphertext
d. Confusion means makes relationship between ciphertext and key as complex as possible
e. All of above are correct answers
Questions and Answers (30%) – please write your answer on the blank area of the test sheets. Don’t spend too much
time to write long answer for each question. Try to be as neat and short as possible.
1.
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5.
What is the purpose of S-Boxes in DES? (5%)
Please use a diagram to represent the infrastructure of PK (Public Key Encryption). (5%)
What are differences between Rijndael and AES cipher? (5%)
What is the purpose of State Array in AES cipher? (5%)
Please use a diagram to represent how to implement authentication and digital signature with
encryption? (10%)
Comments (10%) – Please indicate what can I do to improve this class for your study.
- Good Luck to your test..