A penetration tester has gained the ability to submit arbitrary plaintexts to an encryption oracle and receive the corresponding ciphertexts. The target uses a block cipher in ECB mode. Which attack would be most effective to demonstrate a weakness?

Perform a meet-in-the-middle attack by encrypting from both ends.

Use a rainbow table of common plaintext blocks to reverse the ciphertext.

Capture a large amount of ciphertext and perform frequency analysis on the blocks.

Submit plaintext blocks with controlled differences and observe the ciphertext to detect patterns and infer plaintext structure.

A network administrator is implementing a secure communication protocol between two servers. The administrator is concerned about man-in-the-middle attacks and replay attacks. Which combination of measures would best mitigate both threats?

Use mutual authentication (e.g., TLS with client certificates) and include a nonce or timestamp in each message.

Use a strong encryption algorithm (e.g., AES-256) and a long key.

Use a hash function with a large output size for message digests.

Use a VPN tunnel between the servers.

What is the primary characteristic of a dictionary attack?

It relies on analyzing ciphertext frequency

It uses a precompiled list of likely passwords or keys

It tries all possible combinations of characters

It exploits mathematical relationships between keys

Which cryptographic construction is most vulnerable to a meet-in-the-middle attack?

Double encryption with two independent keys

A single encryption with a long key

EC-CouncilCertified Ethical Hacker

Domain 9Objective 3

Cryptanalysis and Attacks CEH Practice Questions (Page 3)

Part of the Cryptography domain, which makes up ~9% of our current practice bank. EC-Council does not publish an official question count, but from its 240-minute exam (~95–160 total, ~9–14 in this domain), expect 2–4 from this objective — we provide 63 practice questions to prepare you well beyond it. (estimate)

63questions here

13free pages

16concepts

16 Concepts in This Objective

Cryptanalysis Fundamentals
Types of Cryptanalytic Attacks
Brute-Force Attack
Dictionary Attack
Rainbow Table Attack
Frequency Analysis
Known-Plaintext Attack
Chosen-Plaintext Attack
Chosen-Ciphertext Attack
Related-Key Attack
Side-Channel Attacks
Man-in-the-Middle Attack
Replay Attack
Birthday Attack
Meet-in-the-Middle Attack
Cryptanalytic Tools and Techniques

Questions 11–15

11application · medium
A penetration tester has gained the ability to submit arbitrary plaintexts to an encryption oracle and receive the corresponding ciphertexts. The target uses a block cipher in ECB mode. Which attack would be most effective to demonstrate a weakness?
Select an answer first
12expert · hard
A network administrator is implementing a secure communication protocol between two servers. The administrator is concerned about man-in-the-middle attacks and replay attacks. Which combination of measures would best mitigate both threats?
Select an answer first
13expert · hard
A security team is evaluating the strength of a custom encryption algorithm used in a legacy system. The team has the ability to submit chosen plaintexts to the system and observe the ciphertexts, but they do not have access to the decryption function. They also have a limited set of known plaintext-ciphertext pairs. Which attack model gives the team the most powerful capability to analyze the algorithm?
Select an answer first
14foundation · easy
What is the primary characteristic of a dictionary attack?
Select an answer first
15foundation · easy
Which cryptographic construction is most vulnerable to a meet-in-the-middle attack?
Select an answer first

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