Kelsey Lewis has been working as a cloud security engineer in a BPO company that provides 24 × 7 customer service. Owing to the cost-effective storage and security features provided by cloud computing, her organization adopted the cloud environment 4 years ago. Kelsey implemented the TLS protocol to provide security to e-mail communications, voice over IP (VoIP) communication, web traffic, messaging clients, file transfers, and internet services (Domain Name Service (DNS) and Network Time Protocol (NTP)). Which certificate is used by TLS for communication authentication and encryption between hosts?