Final answer:
The correct answer is a) Certificate Authority (CA), which issues digital certificates to validate the ownership of encryption keys used in secure communications.
Step-by-step explanation:
The description "Issue digital certificates that validate the ownership of encryption keys used in secure communications and are based on a trust model" fits the role of a Certificate Authority (CA). A CA is a trusted entity that issues digital certificates, which include the public key part of a key pair used in encryption and cryptographic authentication. These digital certificates verify that a particular public key belongs to the entity identified in the certificate. This system underpins various security protocols on the internet, including SSL/TLS, ensuring safe and secure transactions and communications.