What type of encryption uses both public and private keys for secure communications?

Asymmetric encryption is a cryptographic method that employs a pair of keys: a public key, which can be shared with anyone, and a private key, which is kept secret by the owner. This dual-key system is fundamental for secure communications, as it allows data to be encrypted with the recipient's public key and can only be decrypted by the corresponding private key held by that recipient. This ensures confidentiality, as only the intended recipient can access the plaintext.

Key advantages of asymmetric encryption include the ability to establish secure connections over unsecured channels without needing to share secret keys in advance, which is a critical aspect in scenarios like SSL/TLS communications. Additionally, it enables the use of digital signatures, providing authentication and non-repudiation for messages, further enhancing the security framework.

In contrast, symmetric encryption relies on a single shared key for both encryption and decryption, while hash encryption is primarily used for verifying data integrity rather than for encryption in the traditional sense. Block encryption refers to a specific method of implementing symmetric encryption, focusing on how data is processed in fixed-size blocks, but it does not utilize a key pair like asymmetric encryption. Therefore, asymmetric encryption is the most appropriate choice when discussing secure communications that involve both public and private keys.