Essentials of Cyber Security — Quiz-4 Answer (Amrita University — Ahead Online BCA Quiz Answer)

1. How can we prevent replay attacks?
Group of answer choices

Option 1. By making use of random numbers sourced from both client and server to generate the symmetric keys

Option 2. By using hybrid encryption schemes instead of public key encryption schemes

Option 3. By blacklisting the IP’s that we assume to be Eve’s

Option 4. By making sure that the message is both encrypted and authenticated (data origin authentication)

ANSWER —By making use of random numbers sourced from both client and server to generate the symmetric keys

2. Block cipher operates on blocks of data of specific length. What happens when the message length is not a multiple of the block length?
Group of answer choices

Option 1. The remaining bytes can be discarded

Option 2. The remaining bytes can be encrypted using another algorithm whose block length matches with the length of remaining bytes.

Option 3. We can append some padding bytes to make another valid block

Option 4. Only messages whose length is a multiple of the block size can be encrypted

ANSWER — We can append some padding bytes to make another valid block

3. A cipher is said to have the property of confusion but not diffusion if

Option 1. changing a single plaintext bit would change multiple bits within the ciphertext, but at the same time, changing a single bit of the key wouldn’t change multiple bits within the ciphertext

Option 2. changing a single key bit would change multiple bits within the the ciphertext but at the same time, changing a single bit of the plaintext wouldn’t change multiple bits within the ciphertext

Option 3. changing a single key bit would change multiple bits within the plaintext and the ciphertext but at the same time, changing a single bit of the the ciphertext key wouldn’t change multiple bits within the plaintext and the key

Option 4. changing a single key bit would change multiple bits within the plaintext but at the same time, changing a single bit of the ciphertext wouldn’t change multiple bits within the key

ANSWER — changing a single key bit would change multiple bits within the the ciphertext but at the same time, changing a single bit of the plaintext wouldn’t change multiple bits within the ciphertext

4. Asymmetric encryption schemes usually require larger keys when compared to symmetric encryption schemes because

Option 1. symmetric keys can be essentially random while asymmetric keys should have specific properties

Option 2. Asymmetric encryption schemes only work on large keys

Option 3. Asymmetric encryption schemes are more brittle compared to symmetric encryption schemes

Option 4. Asymmetric encryption doesn’t rely on shared keys

ANSWER — symmetric keys can be essentially random while asymmetric keys should have specific properties