How does a public key infrastructure (PKI) work?

• A. It uses a single key for encryption and decryption
• B. It uses a pair of keys to secure data transmission
• C. It utilizes biometric authentication for access control
• D. It relies solely on passwords for user verification

Answer: (B)

A public key infrastructure (PKI) is designed to provide a framework for secure communications using asymmetric cryptography, which involves the use of two separate keys: a public key and a private key. The public key is made available to anyone who wants to send encrypted data, while the private key is kept secret by the owner and is used to decrypt the information.

This system allows for secure data transmission because it ensures that even if the public key is intercepted while being shared, only the holder of the corresponding private key can decrypt messages that were encrypted with the public key. This method also supports authentication, as it can confirm the identity of the sender when they sign a message with their private key, allowing others to verify their identity using the sender's public key.

The other options mention different security mechanisms that do not apply to how PKI functions. For instance, the use of a single key for encryption and decryption refers to symmetric encryption, which is different from the dual-key approach of PKI. Biometric authentication and relying solely on passwords pertain to identity verification methods but are not central to the PKI framework itself.