# Symmetric Ciphers Questions and Answers – Pseudorandom Number Generators and Stream Ciphers – III

This set of Cryptography Multiple Choice Questions & Answers (MCQs) focuses on “Pseudorandom Number Generators and Stream Ciphers”.

1. Which mode is recommend for the NIST SP 800-90 Random number generator?
a) OFB
b) CBC
c) CFB
d) CTR

Explanation: OFB is the recommended mode for the NIST SP 800-90 Random number generator.

2. ANSI X9.17 uses which cryptographic algorithm?
a) DES
b) AES
c) RC5
d) 3DES

Explanation: ANSI X9.17 uses the Triple DES (3DES) algorithm.

3. Pretty Good Privacy(PGP) uses which PRNG?
a) ANSI X9.82
b) RFC 4086
c) NIST SP 800-90
d) ANSI X9.17

Explanation: Pretty Good Privacy(PGP) uses ANSI X9.17 as its PRNG.

4. Which of the following statements are true?
i) Stream Ciphers are fasters than Block Ciphers
ii) Block Ciphers can reuse keys
iii) Block ciphers use lesser code than stream ciphers

a) 1st and 2nd
b) 1st only
c) 2nd and 3rd
d) All are true

Explanation: Block ciphers use more code than stream ciphers.
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5. Which of the following statements are true?
i) RC4 is used in SSL/TLS
ii) File transfer, e-mail use stream ciphers
iii) Browser/Web Links use stream ciphers

a) 1st and 2nd
b) 1st only
c) 1st and 3rd
d) All are true

Explanation: File transfer, e-mail use block ciphers.

6. Which of the following statements are true?
i) PRNGs are slower than TRNGs
ii) PRNGs are periodic
iii) TRNGs are nondeterministic

a) 1st and 2nd
b) 1st only
c) 2nd and 3rd
d) All are true

Explanation: PRNGs are faster than TRNGs.

7. Deskewing is a method to modify bit stream to reduce bais that has been developed.
a) True
b) False

Explanation: The statement is true.

8. Intel digital random number generator uses which among the following methods to generate random bits?
a) pulse detectors of ionizing radiating events
b) gas discharge tubes
c) wind resistance
d) thermal noise

Explanation: Intel DRNGs use thermal noise for generation of the random bits.

9. Which of the following AES modes is used in the Intel DRNG?
i) AES CFB
ii) AES CTR
iii) AES CBC
iv) AEC OFB

a) 2nd and 3rd
b) 3rd and 4th
c) 1st and 2nd
d) All of the mentioned

Explanation: AES CTR and AES CBC are the 2 modes used in the INTEL DRNGs.

10. The number of transistors used in the INTEL DRNG
a) 8
b) 2
c) 4
d) 5

Explanation: 2 transistors are used which toggle the randomly generated bit from the thermal source.

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