Cryptography Quiz

Question 1: What is the closest precise meaning of ‘Cryptography’?
a. A technique of military communication.
b. A study of hiding secret messages through encryption.
c. A study of principles/methods of deciphering ciphertext without knowing the key.
d. A technique of embedding one message into another.

Solution:  A study of hiding secret messages through encryption.

Question 2: What is the closest meaning of ‘Cryptanalysis’?
a. A study of principles/methods of deciphering ciphertext without knowing the key.
b. A technique of military communication.
c. A technique of embedding one message into another.
d. A study of hiding secret messages through encryption.

Solution: A study of principles/methods of deciphering ciphertext without knowing the key.

Question 3: Which ONE (1) of the following is NOT a security issue?
a. How can we know the technology used in a particular software?
b. How can we tell whether an email from a potential client is a genuine inquiry from the person that it claims to have come from?
c. How can we be sure that the content of an electronic file have not been altered?
d. How can we be sure that the email that we sent contains no malware?

Solution: How can we know the technology used in a particular software?

Question 4: Which ONE (1) of the following terms is defined by this statement: ‘A potential for violation of security, which exists when there is a circumstance, capability, action, or event that could breach security and cause harm’?
a. Exploit
b. Attack
c. Threat
d. Vulnerability

Solution: Threat

Question 5: A __________________ encrypts each plaintext digit one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream.
a. Block cipher
b. Stream cipher
c. RSA algorithm
d. Single Transposition Cipher

Solution: Stream cipher

Question 6: The term ‘Diffusion’ was introduced by Claude Shannon to thwart cryptanalysis based on statistical analysis. Which one of the following best describes the definition of this term?
a. The relationship between the statistics of the ciphertext and the value of the encryption key is made as complex as possible.
b. The statistical structure of the plaintext is dissipated into long range statistics of the ciphertext.
c. No elements are added or deleted or replaced in the sequence, rather the order in which the elements appear in the sequence is changed.
d. Each plaintext element or group of elements is uniquely replaced by a corresponding ciphertext element or group of elements.

Solution: The statistical structure of the plaintext is dissipated into long range statistics of the ciphertext.

Question 7: Which one of the following is NOT TRUE about Data Encryption Standard (DES)?
a. It has 3 variants namely DES-128, DES-192 and DES-256.
b. Data are encrypted in 64-bit blocks using a 56-bit key.
c. It was issued in 1977 by the United States National Bureau of Standards (now NIST) as Federal Information Processing Standard 46.
d. DES was broken due to differential attack that can deduce the key in less than 2^(56) time complexity.

Solution: It has 3 variants namely DES-128, DES-192 and DES-256.

Question 8: Which of the following contribute(s) to the failure of DES?
a. DES was designed to survive for less than 7 years.
b. The key length is short. Easy to conduct brute force attack.
c. The key length is sufficient. However, the round function is quite simple to perform reverse engineering.
d. DES produces poor avalanche effect.

Solution: The key length is short. Easy to conduct brute force attack.
DES produces poor avalanche effect.

Question 9: Why 3DES is still secure though DES was broken?
a. Because 3DES has 48 rounds.
b. Because the subkeys used are different for each round.
c. Because 3DES has 32 rounds.
d. Because 3DES does not implement the actual structure of DES.

Solution: Because 3DES has 48 rounds.
Because the subkeys used are different for each round.

Question 10: Which of the following is the transformation in AES that represent(s) Substitution?
a. MixColumn
b. AddRoundKey
c. SubByte
d. ShiftRow

Solution: SubByte

Question 11: Why the size of ciphertext is longer than the size of plaintext?
a. No, the size of the ciphertext is the same as the size of the plaintext.
b. Because there are some bits are padded to the last block of plaintext to make it a size of a defined block.
c. Because there are additional bits in subkeys are added up to the plaintext block during the encryption.
d. Because some bits in plaintext are removed during the encryption.

Solution: Because there are some bits are padded to the last block of plaintext to make it a size of a defined block.

Question 12: AES has three variants, namely AES-128, AES-192 and AES-256. In which applications that these three variants are used, respectively?
a. Military, E-Commerce, Government
b. Military, Government, E-Commerce
c. E-Commerce, Government, Military
d. Government, E-Commerce, Military

Solution: E-Commerce, Government, Military

Question 13: Why do you think AES is still secure until now?
a. The key length is long and makes it still infeasible to be broken.
b. AES implements low number of rounds.
c. AES has strong avalanche effect.
d. The structure is understandable but difficult to deduce the key.

Solution: The key length is long and makes it still infeasible to be broken.
AES has strong avalanche effect.
The structure is understandable but difficult to deduce the key.

Question 14: Which of the following represent(s) transposition in AES?
a. ShiftRow
b. SubByte
c. MixColumn
d. AddRoundKey

Solution: ShiftRow
MixColumn

Question 15: Which of the following is NOT TRUE about DES?
a. Though DES was broken, it was once useful for government.
b. DES was not used in any application before.
c. Though DES was broken, it was once useful for e-commerce.
d. Though DES was broken, it is still useful for military.

Solution: DES was not used in any application before.
Though DES was broken, it is still useful for military.