WGU D830/D334 INTRODUCTION TO CRYPTOGRAPHY OA FINAL EXAM – 300 QUESTIONS 2026/2027 EDITION – VERIFIED QUESTIONS & ANSWERS (100% VERIFIED ANSWERS) WITH RATIONALES | ALREADY GRADED A+

WGU D830/D334 INTRODUCTION TO CRYPTOGRAPHY OA FINAL
EXAM – 300 QUESTIONS 2026/2027 EDITION –
VERIFIED QUESTIONS & ANSWERS (100% VERIFIED ANSWERS)
WITH RATIONALES | ALREADY GRADED A+

DOMAIN 1 – CRYPTOGRAPHIC PRINCIPLES, MATHEMATICS & HISTORY
(Questions 1–50)
1. Which cryptographic principle ensures that the sender of a message cannot
later deny having sent it?
A. Confidentiality
B. Integrity
C. Nonrepudiation
D. Availability

Correct Answer: C

Rationale: Nonrepudiation prevents a sender from falsely denying their
actions, typically achieved by signing data with the sender's unique private
key. Confidentiality protects data from unauthorized access, integrity
ensures data has not been altered, and availability ensures data is
accessible when needed.

2. What mathematical operation calculates the remainder when one integer is
divided by another, forming the basis of modular arithmetic?
A. Matrix multiplication
B. Modulo (mod) operator
C. Greatest Common Divisor (GCD)
D. Exclusive OR (XOR)

Correct Answer: B

Rationale: The modulo operator calculates the remainder after division,
which creates the cyclic mathematical fields required for modern encryption
algorithms. Matrix multiplication is used in some ciphers, GCD is used in
key generation, and XOR is a bitwise operation used in stream ciphers.

3. What is Kerckhoffs's Principle and why is it fundamental to modern

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, cryptography?
A. The algorithm must be kept secret at all times
B. A cryptosystem should remain secure even if everything except the key is
public
C. Keys should be as short as possible for efficiency
D. Only government-approved algorithms should be used

Correct Answer: B

Rationale: Kerckhoffs's principle states that a cryptosystem should be
secure even if everything about the system, except the key, is public
knowledge. This allows algorithms to be publicly scrutinized and standardized
(like AES), with security depending solely on key secrecy.

4. What is the difference between confusion and diffusion?
A. Confusion spreads plaintext bits; diffusion hides key relationships
B. Confusion obscures the relationship between key and ciphertext; diffusion
spreads plaintext influence over many ciphertext bits
C. Confusion is used in stream ciphers; diffusion in block ciphers
D. They are the same concept with different names

Correct Answer: B

Rationale: Confusion makes the relationship between the key and ciphertext
complex, while diffusion spreads the influence of one plaintext bit over many
ciphertext bits. These Shannon concepts thwart statistical analysis.

5. Why is the One-Time Pad (OTP) theoretically unbreakable?
A. It uses extremely long keys
B. It has never been successfully attacked
C. Ciphertext reveals no information about plaintext with truly random,
single-use keys as long as the message
D. It uses quantum mechanics

Correct Answer: C

Rationale: OTP provides perfect secrecy when the key is truly random, used
only once, and as long as the message. However, key distribution and

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,management make it impractical. It does not rely on quantum mechanics.

6. In the Vigenère cipher, what is the Kasiski examination used to determine?
A. The encryption algorithm
B. The length of the keyword
C. The plaintext language
D. The sender's identity

Correct Answer: B

Rationale: The Kasiski examination finds repeated sequences in ciphertext
and analyzes distances between them to determine keyword length, the first
step in breaking polyalphabetic ciphers.

7. What is the primary vulnerability of Electronic Codebook (ECB) mode?
A. It is too slow
B. Identical plaintext blocks produce identical ciphertext blocks,
revealing patterns
C. It requires too much memory
D. It cannot handle large files

Correct Answer: B

Rationale: ECB encrypts each block independently with the same key, so
patterns in plaintext appear in ciphertext. Images encrypted with ECB may
still show silhouettes.

8. Which cryptographic principle ensures that data has not been altered
during transmission?
A. Confidentiality
B. Integrity
C. Nonrepudiation
D. Authentication

Correct Answer: B

Rationale: Integrity ensures that data has not been modified in transit,
typically verified through hash functions or message authentication codes

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, (MACs). Confidentiality protects data from unauthorized viewing,
nonrepudiation prevents denial of sending, and authentication verifies
identity.

9. What is the difference between a block cipher and a stream cipher?
A. Block ciphers encrypt data one bit at a time; stream ciphers encrypt
fixed-size blocks
B. Block ciphers encrypt fixed-size blocks of data; stream ciphers encrypt
data one bit or byte at a time
C. Block ciphers are symmetric; stream ciphers are asymmetric
D. There is no difference

Correct Answer: B

Rationale: Block ciphers operate on fixed-size blocks of plaintext
(e.g., 128 bits for AES), while stream ciphers encrypt data continuously,
one bit or byte at a time, making them suitable for data streams.

10. What is the purpose of the Exclusive OR (XOR) operation in cryptography?
A. To perform modular arithmetic
B. To combine plaintext with a key stream in stream ciphers
C. To generate prime numbers
D. To compute hash values

Correct Answer: B

Rationale: XOR is a fundamental bitwise operation used in stream ciphers to
combine the plaintext with the key stream. It is also used in many block
cipher operations due to its reversible nature.

11. What is a "brute force attack" in cryptanalysis?
A. An attack that exploits a mathematical weakness in the algorithm
B. An attack that tries every possible key until the correct one is found
C. An attack that uses social engineering to obtain the key
D. An attack that intercepts the key during transmission

Correct Answer: B


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