Question

if a bit error occurs in the transmission of a ciphertext character in 8-bit cfb mode, then after decryption, how many blocks of plaintext will be affected? assume the block size is 32 bits?

Answer 1

In 8-bit CFB mode, if a bit error occurs in the transmission of a ciphertext character, only the corresponding plaintext character will be affected.

Step-by-step explanation:

In CFB (Cipher Feedback) mode, each plaintext block is XORed with the output of the encryption function to produce the ciphertext block. If a bit error occurs in the transmission of a ciphertext character in 8-bit CFB mode, only the corresponding plaintext character will be affected. This means that only one block of plaintext (32 bits) will be affected.

Answer 2

In 8-bit CFB mode, a bit error in the transmission of a ciphertext character will affect 31 blocks of plaintext.

Why would the blocks be affected ?

In 8-bit CFB mode, each ciphertext block is typically 8 bits (1 byte) in size, and a bit error in a ciphertext block can indeed affect 31 blocks of plaintext.

This is because CFB mode operates by encrypting the previous ciphertext block and then XORing the result with the plaintext to produce the ciphertext for the current block. If a bit error occurs in a ciphertext block, it will propagate to the next 8 ciphertext blocks, causing decryption errors in the corresponding 31 blocks of plaintext.