**RSA encryption requires a longer key length to provide the same level of security as symmetric encryption. Which of the following is incorrect or least related to this fact? (Wentz QOTD)**

A. RSA encryption requires more CPU cycles

B. RSA depends on prime numbers and boolean operations to encrypt data

C. RSA encryption typically encrypts plaintext of which the size is smaller than 512 bytes

D. The number of prime numbers to shape the keyspace is far less than natural numbers

**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 B. RSA depends on prime numbers and boolean operations to encrypt data.

Wentz’s book, *The Effective CISSP: Security and Risk Management*, helps CISSP and CISM aspirants build a solid conceptual security model. It is a tutorial for information security and a supplement to the official study guides for the CISSP and CISM exams and an informative reference for security professionals.

Asymmetric cryptography relies on **mathematic computations,** while symmetric cryptography relies on bitwise or **boolean operations**. RSA cryptography uses prime numbers to derive the key pair. The number of prime numbers is far less than natural numbers, and that results in a much longer key size to create sufficient keyspace and consumes more CPU cycles.

# Reference

**RSA 加密需要更長的密鑰長度才能提供與對稱加密相同的安全級別。 以下哪一項是不正確的或與上述事實最不相關？ (Wentz QOTD)**

A. RSA 加密需要更多的 CPU 週期

B. RSA 依賴質數和布林(boolean)運算來加密數據

C. RSA 加密一般對小於 512 字節的明文進行加密

D. 塑造keyspace的質數數量遠少於自然數