Which protocol standard is used to encrypt and digitally sign emails with attachments and provides the CIA triad plus non-repudiation?

Which protocol standard is used to encrypt and digitally sign emails with attachments and provides the CIA triad plus non-repudiation?

• A. PGP
• B. SSL
• C. SSH
• D. S/MIME

Answer: (D)

End-to-end email security that encrypts content and provides a verifiable signature for authenticity and non-repudiation is achieved with S/MIME. It uses X.509 certificates and a PKI to sign messages (proving who sent them) and to encrypt the content so that only the intended recipient can read it. This means the entire MIME message, including attachments, is protected — setting up confidentiality, integrity, and non-repudiation through the digital signature. S/MIME is a standardized, client-friendly approach that many email systems support out of the box, making it a common choice for securing corporate email. While PGP also offers encryption and signing, S/MIME relies on a centralized certificate authority model, which is a key difference. SSL/TLS protects the path between client and server rather than the email content itself, and SSH is for remote access and file transfers, not email encryption.

End-to-end email security that encrypts content and provides a verifiable signature for authenticity and non-repudiation is achieved with S/MIME. It uses X.509 certificates and a PKI to sign messages (proving who sent them) and to encrypt the content so that only the intended recipient can read it. This means the entire MIME message, including attachments, is protected — setting up confidentiality, integrity, and non-repudiation through the digital signature. S/MIME is a standardized, client-friendly approach that many email systems support out of the box, making it a common choice for securing corporate email.

While PGP also offers encryption and signing, S/MIME relies on a centralized certificate authority model, which is a key difference. SSL/TLS protects the path between client and server rather than the email content itself, and SSH is for remote access and file transfers, not email encryption.