Which security measure BEST provides non-repudiation in electronic mail?

A.
Digital signature

B.
Double length Key Encrypting Key (KEK)

C.
Message authentication

D.
Triple Data Encryption Standard (DES)

Explanation:
A tool used to provide the authentication of the sender of a message. It can verify
the origin of the message along with the identity of the sender. IT is unique for every transaction
and created with a private key. – Shon Harris All-in-one CISSP Certification Guide pg 930
“Secure Multipurpose Internet Mail Extensions (S/MIME) offers authentication and privacy to email through secured attachments. Authentication is provided through X.509 digital certificates.
Privacy is provided through the use of Public Key Cryptography Standard (PKCS) Enryption. Two
types of messages can be formed using S/MIME: signed messages and enveloped messages. A
signed message provides integrity and sender authentication. An enveloped message provides
ntegrity, sender authentication, and confidentiality.” Pg 123 Tittle: CISSP Study Guide