Question

Which of the following can be classified under advantages and disadvantages of OFB mode?

i) Transmission errors

ii) A bit error in a ciphertext segment

iii) Cannot recover from lost ciphertext segments

iv) Ciphertext or segment loss

(a) a) Advantages: None; Disadvantages: All

(b) Advantages: All; Disadvantages: None

(c) Advantages: i); Disadvantages: ii) iii) iv)

(d) Advantages: i); ii) Disadvantages: iii) iv)

The question was posed to me in my homework.

I'd like to ask this question from DES Modes of Operation in section Advanced Encryption Algorithm and Block Cipher Operation of Cryptograph & Network Security

Answer 1

Right answer is (d) Advantages: i); ii) Disadvantages: iii) iv)

The explanation is: Advantages:

More resistant to transmission errors.

A bit error in a ciphertext segment affects only the decryption of that segment.

Disadvantages:

Cannot recover from lost ciphertext segments.

If a ciphertext segment is lost, all following segments will be decrypted incorrectly (if the receiver is not aware of the segment loss).