CISSP PRACTICE QUESTIONS – 20210205

Effective CISSP Questions

You are learning cryptography. Which of the following is correct?
A. Secret-key encryption uses a shorter key than public-key encryption to achieve a lower work factor.
B. The CBC mode of public-key encryption hides ciphertext patterns, while ECB doesn’t.
C. Block ciphers have better performance than stream ciphers on constrained hardware.
D. Stream ciphers are more vulnerable to cryptanalytic attacks than block ciphers.

Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.

My suggested answer is D. Stream ciphers are more vulnerable to cryptanalytic attacks than block ciphers.

Credit: Guang Gong, University of Waterloo
Credit: Guang Gong, University of Waterloo

Speed, security, and simplicity are primary concerns for designing new encryption. The simplicity in view of software implementation is often quite complex in the hardware implementation. “The hardware implementations of today’s algorithms, such as AES cipher, are inefficient for devices with limited hardware area. So, stream ciphers are used in cases that the low hardware complexity is necessitated.” (Paris Kitsos)

  • Secret-key encryption can use a shorter key than public-key encryption to achieve an equal or higher work factor.
  • The CBC mode of secret-key encryption hides ciphertext patterns, while ECB doesn’t. Even though it’s hypothetically possible to use CBC mode in asymmetric encryption, we don’t classify asymmetric ciphers in terms of block or stream.
  • Stream ciphers have better performance than block ciphers on constrained hardware.
  • Stream ciphers are more vulnerable to cryptanalytic attacks than block ciphers.

Reference

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您正在學習密碼學。 以下哪項是正確的?
A. 密鑰(secret-key)加密使用比公鑰(public-key)加密更短的金鑰來實現較低的工作係數(work factor)。
B. 公鑰加密的CBC模式隱藏密文的樣態(pattern),但ECB模式則不會。
C. 區塊型(block)加密器在資源有限的硬體上比串流型(stream)加密器具有更好的性能。
D. 串流型加密器比區塊型加密器更容易受到密碼分析攻擊。

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