CompTIA CASP CAS-004 Question # 21 Topic 4 Discussion

Cipher feedback (CFB) is a mode of operation for block ciphers that allows them to encrypt streaming data. CFB uses an initialization vector (IV) and a block cipher to generate a keystream that is XORed with the plaintext to produce the ciphertext. CFB has low latency because it can encrypt each byte or bit of plaintext as soon as it arrives, without waiting for a full block. CFB is suitable for streaming data because it does not require padding or block synchronization.

B. Cipher block chaining message authentication code (CBC-MAC) is a mode of operation for block ciphers that provides both encryption and authentication. CBC-MAC uses an IV and a block cipher toencrypt the plaintext and generate a MAC value that is appended to the ciphertext. CBC-MAC has high latency because it requires the entire message to be processed before generating the MAC value. CBC-MAC is not suitable for streaming data because it requires padding and block synchronization.

C. Cipher block chaining (CBC) is a mode of operation for block ciphers that provides encryption only. CBC uses an IV and a block cipher to encrypt each block of plaintext by XORing it with the previous ciphertext block. CBC has high latency because it requires a full block of plaintext before encryption. CBC is not suitable for streaming data because it requires padding and block synchronization.

D. Electronic codebook (ECB) is a mode of operation for block ciphers that provides encryption only. ECB uses a block cipher to encrypt each block of plaintext independently. ECB has low latency because it can encrypt each block of plaintext as soon as it arrives. However, ECB is not suitable for streaming data because it requires padding and block synchronization. Moreover, ECB is insecure because it does not use an IV and produces identical ciphertext blocks for identical plaintext blocks.