Question

When using _____________ mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This means there is significantly more randomness in the final ciphertext. This is much more secure than electronic codebook mode and is the most common mode. A) ECB (Electronic Codebook)

B) CBC (Cipher Block Chaining)

C) CFB (Cipher Feedback)

D) OFB (Output Feedback)

Answer 1

CBC (Cipher Block Chaining) mode adds security to block ciphers by XORing each block of plaintext with the previous ciphertext block before encryption, preventing evident patterns and ensuring more randomness in the ciphertext.

Step-by-step explanation:

When using CBC (Cipher Block Chaining) mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted, as mentioned in the question. This process of mixing the plaintext with the previous ciphertext adds a layer of complexity which in turn increases security, since each block of ciphertext depends on the encryption of the previous block. This means that any change in a plaintext block will affect all subsequent ciphertext blocks, creating significantly more randomness in the final ciphertext compared to modes like ECB (Electronic Codebook). Essentially, in CBC mode, the dependency on previous blocks prevents patterns from becoming evident in the ciphertext, which is particularly useful in preventing certain types of cryptanalysis. This is one of the reasons why CBC is generally considered to be more secure than ECB, and as such, is one of the most commonly used modes of encryption.