What does an asymmetric key use to decrypt data?

In asymmetric encryption, a key pair consists of a public key and a private key. When data is encrypted using a public key, it can only be decrypted with the corresponding private key. This unique relationship between the keys is central to the concept of asymmetric cryptography, which is widely used for secure data transmission over the internet, such as in SSL/TLS protocols.

The private key is kept secret by the owner, while the public key is distributed openly. This design allows anyone to encrypt data for the owner using the public key, while only the owner can decrypt it using their private key. Thus, the security of asymmetric encryption relies on the private key's confidentiality.

The other choices do not apply in this context; a public key can encrypt data but cannot decrypt it. A hash function is used for integrity checks, creating a fixed-size hash value from data, and does not involve encryption or decryption processes. A shared key, related to symmetric encryption, is a single key shared between parties for both encryption and decryption, which does not represent the asymmetric key system. Therefore, the private key is the necessary component to decrypt data that was encrypted using the corresponding public key.