Cryptography Quiz

Which of the following correctly differentiates a stream cipher from a block cipher?

• Stream ciphers encrypt fixed-size blocks, while block ciphers encrypt individual bits.

• Stream ciphers operate on continuous streams of data, while block ciphers work on discrete blocks of bits.

• Both encrypt fixed-size data blocks but differ in key length.

• Stream ciphers and block ciphers use identical key scheduling techniques.

Which of the following stream ciphers uses a synchronous keystream generator approach?

• RC4

• DES

• AES

• Blowfish

In symmetric key cryptography, the primary challenge is:

• Large key sizes affecting computational efficiency

• Secure key distribution between sender and receiver

• High computational complexity of public key operations

• Vulnerability to chosen-ciphertext attacks only

Which block cipher mode of operation turns a block cipher into a self-synchronizing stream cipher?

• Cipher Block Chaining (CBC)

• Cipher Feedback Mode (CFB)

• Output Feedback Mode (OFB)

• Counter Mode (CTR)

A stream cipher can be more vulnerable to which of the following if the same key is reused?

• Replay attacks

• Frequency analysis

• Key collision attacks

• Two-time pad attack

The avalanche effect in block ciphers ensures:

• Minor key changes produce identical ciphertexts

• Small plaintext changes drastically alter ciphertext

• Large plaintext changes leave ciphertext mostly unchanged

• Key length does not affect ciphertext properties

Which of the following block cipher algorithms uses a Feistel network structure?

• AES

• RC4

• DES

• ChaCha20

In stream ciphers, the keystream is generated:

• By XORing the plaintext with a fixed key directly

• From a pseudorandom sequence generator seeded with the key

• Using public key algorithms for each bit

• By dividing the plaintext into fixed-size blocks

Which of the following is a disadvantage of block ciphers compared to stream ciphers?

• Inability to encrypt large messages

• Higher error propagation

• Lower throughput for real-time applications

• Lack of diffusion property

Which property of stream ciphers makes them preferable in certain real-time systems over block ciphers?

• Block-wise data encryption

• Lower error propagation

• Higher computational complexity

• Requirement for padding schemes