GSEC · Question #124
What is the key difference between Electronic Codebook mode and other block cipher modes like Cipher Block Chaining, Cipher-Feedback and Output-Feedback?
The correct answer is C. Plaintext patterns encrypted with the same key will always generate the same Cipher text pattern. ECB mode encrypts each plaintext block independently with the same key, so identical plaintext blocks always produce identical ciphertext blocks, exposing data patterns that other modes prevent.
Question
What is the key difference between Electronic Codebook mode and other block cipher modes like Cipher Block Chaining, Cipher-Feedback and Output-Feedback?
Options
- APlaintext patterns are concealed by XO Ring with previous cipher text block but input to the block
- BPlaintext patterns are concealed and input to the block cipher is randomized by XO Ring with
- CPlaintext patterns encrypted with the same key will always generate the same Cipher text pattern
- DPlaintext patterns are not concealed but input to the block cipher is randomized by XO Ring with
How the community answered
(51 responses)- A4% (2)
- B16% (8)
- C75% (38)
- D6% (3)
Why each option
ECB mode encrypts each plaintext block independently with the same key, so identical plaintext blocks always produce identical ciphertext blocks, exposing data patterns that other modes prevent.
XORing each block with the previous ciphertext block before encryption describes Cipher Block Chaining (CBC) mode, which is one of the alternative modes specifically designed to conceal plaintext patterns.
Randomizing block cipher input via XOR with a keystream or feedback value describes Output Feedback or Cipher Feedback modes, not ECB, which performs no such randomization.
ECB applies the block cipher directly to each block in isolation using the same key with no chaining, feedback, or initialization vector, meaning two identical plaintext blocks always encrypt to the same ciphertext block. This deterministic, pattern-preserving property is ECB's defining weakness - famously demonstrated by the ECB penguin image where visual structure survives encryption - and is precisely what CBC, CFB, and OFB modes are designed to eliminate.
This partially describes CFB or OFB behavior where input randomization occurs - ECB neither conceals patterns nor randomizes input, it simply applies the cipher directly and identically to each independent block.
Concept tested: ECB block cipher mode deterministic pattern leakage
Source: https://csrc.nist.gov/publications/detail/sp/800-38a/final
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