Which of the following is used to authenticate asymmetric keys?

Passwords are shared secrets used for symmetric authentication of users or services, and cannot cryptographically bind or authenticate an asymmetric public key to an identity.

Digital signatures use asymmetric cryptography where a certificate authority signs a public key with its own private key, allowing relying parties to verify the authenticity and integrity of the public key. This process, formalized in X.509 certificates, ensures that the public key genuinely belongs to the claimed entity and has not been tampered with.

A MAC address is a hardware-level data link layer identifier for network interfaces and provides no mechanism for authenticating or validating cryptographic keys.

A DMZ (Demilitarized Zone) is a network segmentation concept that isolates publicly accessible servers from internal networks, and is unrelated to key authentication mechanisms.