Which statement is true regarding key sizes in symmetric vs. asymmetric encryption?

The statement that symmetric encryption requires smaller key sizes for the same level of security is accurate due to the fundamental differences in how symmetric and asymmetric encryption algorithms work. In symmetric encryption, the same key is used for both encryption and decryption, which allows for faster processing and smaller keys to achieve a comparable level of security as asymmetric encryption.

Asymmetric encryption, on the other hand, utilizes a pair of keys—one public and one private. The mathematical frameworks behind asymmetric encryption are inherently more complex, requiring larger key sizes to maintain the same security level. This is because the algorithms involved in asymmetric encryption, like RSA, depend significantly on difficult mathematical problems such as integer factorization and discrete logarithm. Therefore, larger keys are necessary to ensure that the effort needed to break the encryption remains infeasible.

In contrast to this understanding, the other statements do not align with the characteristics of encryption key sizes. For instance, the assertion that key size does not impact security is misleading, as larger key sizes typically enhance security by making cryptanalysis more computationally demanding. The idea that block ciphers have no key size restrictions is also incorrect; most block ciphers have specified key size options that influence their security and performance.