An efficient use of public key infrastructure (PKI) should encrypt the:

A.
entire message.

B.
private key.

C.
public key.

D.
symmetric session key.

Explanation:
Public key (asymmetric) cryptographic systems require larger keys (1,024 bits) and involve intensive and time-consuming computations. In comparison, symmetric encryption is considerably faster, yet relies on the security of the process for exchanging the secret key. To enjoy the benefits of both systems, a symmetric session key is exchanged using public key methods, after which it serves as the secret key for encrypting/decrypting messages sent between two parties.