Which of the following involves the use of a digital certificate issued by a Certificate Authority (CA) to encrypt emails and attachments?

The correct answer is S/MIME (Secure/Multipurpose Internet Mail Extensions) because it specifically utilizes digital certificates issued by a Certificate Authority (CA) to provide a framework for public key encryption and digital signing of email messages. This ensures the confidentiality, integrity, and authenticity of the emails and their attachments.

S/MIME allows users to encrypt emails using the public key of the intended recipient, ensuring that only the recipient can decrypt the message using their private key. Additionally, it provides digital signatures that verify the sender's identity, offering a robust mechanism for secure communication over email.

In contrast, the other options do not pertain to the encryption of emails:

• SSH (Secure Shell) is primarily used for secure remote access and command execution on networked machines, focusing on securely logging into another computer over a network.

• API (Application Programming Interface) is a set of protocols and tools for building software applications, facilitating interaction between different software components, but it does not directly involve email encryption.

• ECDH (Elliptic-Curve Diffie-Hellman) is a key exchange algorithm that allows two parties to establish a shared secret over an insecure channel, primarily used in secure communications, but not specific to email encryption or the use of digital