What is the key difference between Electronic Codebook mode and other block cipher modes like Cipher Block Chaining, Cipher-Feedback and…

The defining characteristic and primary weakness of Electronic Codebook (ECB) mode is its deterministic nature. Each block of plaintext is encrypted independently of all other blocks using the same secret key. Consequently, if two plaintext blocks are identical, their corresponding ciphertext blocks will also be identical. This preserves plaintext patterns, allowing an attacker to infer information about the underlying data structure. In contrast, modes like Cipher Block Chaining (CBC), Cipher-Feedback (CFB), and Output-Feedback (OFB) use an Initialization Vector (IV) and a chaining or feedback mechanism. This ensures that the encryption of each block is dependent on the previous blocks, thus concealing patterns and making identical plaintext blocks result in different ciphertext blocks.

A. This describes a feature of chaining modes like CBC, where plaintext patterns are concealed, not a characteristic of ECB.

B. This accurately describes the benefit of modes like CBC, which is the direct opposite of how ECB functions.

D. This statement is contradictory. Randomizing the input to the block cipher is the very mechanism used to conceal plaintext patterns.

1. National Institute of Standards and Technology (NIST). (2001). Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation. Section 6.1

"Electronic Codebook (ECB) Mode

" states

"The disadvantage of the ECB mode is that identical plaintext blocks are encrypted into identical ciphertext blocks; thus

it does not hide data patterns well."

2. Katz

J.

& Lindell

Y. (2014). Introduction to Modern Cryptography (2nd ed.). CRC Press. In Chapter 3

Section 3.6.2

"Modes of Operation

" the text explains that for ECB

"if mi = mj

then ci = cj

" highlighting that this leaks information about the plaintext.

3. Massachusetts Institute of Technology (MIT) OpenCourseWare. (2017). 6.857 Computer and Network Security

Fall 2017. Lecture 5 notes on Block Ciphers II illustrate this difference

stating for ECB: "Identical plaintext blocks give identical ciphertext blocks. This is BAD." The notes contrast this with CBC

which randomizes the encryption.