BCS515B CNS Quiz-2

In a symmetric cipher model, what must remain secret?

• The algorithm

• The key

• The plaintext

• The ciphertext

Which is NOT a cryptographic system classification dimension?

• Type of operations used

• Number of keys used

• Plaintext processing method

• Communication channel used

What does cryptanalysis aim to recover?

• Ciphertext

• Algorithm

• Key

• Random numbers

Which attack tries all possible keys until the correct one is found?

• Cryptanalysis

• Brute-force attack

• Replay attack

• Differential attack

An encryption scheme is said to be computationally secure if:

• The ciphertext is always random

• It cannot be mathematically described

• Breaking it takes more time/cost than its value

• The key is infinite

Caesar cipher involves shifting letters by:

• 1

• 2

• 3

• 4

The number of possible keys in Caesar cipher is:

• 10

• 25

• 52

• 26!

Caesar cipher is considered insecure because:

• Keys are too long

• Only 25 possible keys exist

• Algorithm is secret

• Uses binary numbers

Which type of substitution cipher uses a permutation of the alphabet?

• Caesar cipher

• Monoalphabetic cipher

• Polyalphabetic cipher

• Vernam cipher

The number of possible keys in a monoalphabetic cipher is:

• 25

• 100

• 26!

• 2^26