Which encryption method involves key pairs for encryption and decryption?

• A. Asymmetric encryption
• B. Symmetric encryption
• C. Stream cipher
• D. Block cipher

Answer: (A)

Asymmetric encryption is the correct choice because it relies on a pair of keys: a public key and a private key. In this methodology, data encrypted with the public key can only be decrypted with the corresponding private key, and vice versa. This allows for secure communication, as one party can share their public key to allow others to send encrypted messages that only the intended recipient can decrypt. This characteristic inherently differentiates asymmetric encryption from methods like symmetric encryption, where a single key is used for both encryption and decryption.

Additionally, stream ciphers and block ciphers are types of symmetric encryption techniques. They process plaintext data in various ways (bit-by-bit for stream ciphers and in fixed-size blocks for block ciphers) but do not utilize key pairs, relying instead on a single shared key for both encryption and decryption. Thus, the use of key pairs in asymmetric encryption is what sets it apart as the correct answer.