What is the difference between symmetric key distribution and public key infrastructure (PKI) in TLS?

• A. PKI uses a shared secret; symmetric key distribution uses certificates.
• B. PKI uses a shared secret; symmetric key distribution uses public/private keys.
• C. Symmetric key distribution uses public/private keys; PKI uses secret keys only.
• D. PKI uses public/private keys to establish trust in TLS.

Answer: (D)

The key idea is that TLS uses a public key infrastructure to establish trust and enable secure key exchange, while symmetric key distribution is about sharing a secret used to encrypt data after a secure channel is set up. In TLS, PKI provides the framework of digital certificates and trusted authorities that bind a server’s identity to a public key. During the handshake, the client verifies the server’s certificate against trusted root authorities, confirming that the public key actually belongs to the server. Once identity is verified, TLS uses public/private key cryptography to securely exchange material that leads to a mutually known symmetric session key. From that point, all communication is encrypted with fast symmetric algorithms using those derived session keys.

So PKI’s role is to establish trust using public/private keys and certificates, enabling a secure key exchange in TLS. In contrast, symmetric key distribution would require sharing a secret key ahead of time and does not by itself provide the identity verification and trust framework that PKI delivers.