Which statement best describes public key cryptography?

• A. It uses a pair of keys, a public key and a private key.
• B. It uses a single shared secret
• C. It uses hash only
• D. It uses symmetric encryption exclusively

Answer: (A)

Public key cryptography relies on a pair of keys: a public key that can be shared openly and a private key kept secret. Messages encrypted with the public key can only be decrypted with the private key, enabling secure communication without a pre-shared secret. It also supports digital signatures by using the private key to sign and the public key to verify, which provides authentication and non-repudiation. In practice, systems often use public-key methods to securely exchange a symmetric key, after which fast symmetric encryption handles the bulk data. The other descriptions describe symmetric or hash-only approaches, which do not capture the two-key, asymmetric nature of public key cryptography.