Which two functions are required for IPsec operation?

Which two functions are required for IPsec operation? (Choose two.)

A.
using AH protocols for encryption and authentication

B.
using SHA for encryption

C.
using Diffie-Hellman to establish a shared-secret key

D.
using PKI for pre-shared-key authentication

E.
using IKE to negotiate the SA

Explanation:
The question wants to know what’s “required”, not “optional”. From the choices, it’s
easier to determine what’s “optional” and/or just plain wrong. Those are answers A, B,
and D. So are C and E correct?
Diffie -Hellman securely establishes a shared secret key over the unsecured medium. So
C is good.
‘use’ IKE to negotiate the SA. However, the negotiation of the SA happens ‘within’ the
protection of the IKE Phase 1 tunnel, so that must be what’s meant.