What is the primary function of a public key in PKI?

• A. To decrypt data securely
• B. To encrypt messages for confidentiality
• C. To authenticate users
• D. To generate unique passwords

Answer: (B)

The primary function of a public key in Public Key Infrastructure (PKI) is to encrypt messages for confidentiality. In asymmetric encryption, which PKI utilizes, a key pair consisting of a public key and a private key is generated. The public key is shared openly and can be used by anyone to encrypt data intended for the owner of the corresponding private key. This ensures that only the person who possesses the private key can decrypt the data, thereby maintaining confidentiality.

When a sender encrypts a message with the recipient's public key, it ensures that only the recipient can access the message after decrypting it with their private key. This mechanism reinforces secure communication over untrusted networks, making the public key a critical component in safeguarding the confidentiality of sensitive information.

While other options mention important security functions, they don't align with the primary purpose of the public key in PKI. For instance, decrypting data securely is the role of the private key, while authentication of users is often achieved through digital signatures that involve both keys but is not the main function of the public key alone. Generating unique passwords is also unrelated to the role of public keys in PKI, as that process often involves different cryptographic techniques.