Question

The _____________ mode turns a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext. A) ECB (Electronic Codebook)

B) CBC (Cipher Block Chaining)

C) CFB (Cipher Feedback)

D) OFB (Output Feedback)

Answer 1

The Output Feedback (OFB) mode turns a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext. The correct answer is (D).

Step-by-step explanation:

The correct answer is (D) OFB (Output Feedback).

The Output Feedback (OFB) mode turns a block cipher into a synchronous stream cipher. In this mode, keystream blocks are generated by encrypting an initial value (IV) with the block cipher. The generated keystream blocks are then XORed with the plaintext blocks to produce the ciphertext.

For example, if we have a plaintext block '10101010' and the corresponding keystream block is '11001100', the resulting ciphertext block will be '01100110', obtained by XORing the two blocks together.