156-315.81.20 Advanced VPN Design Practice Question
Which cryptographic function is primary in verifying the integrity of IKE packets during the negotiation?
⚠ Common exam trap
Candidates often confuse encryption algorithms (like AES) with integrity functions (like SHA-256). They incorrectly select encryption methods, forgetting that integrity specifically requires hashing to detect tampering in transit during IKE negotiation.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SHA-256 hashing.
Integrity is verified using Hashed Message Authentication Codes (HMACs) or similar hashing functions like SHA-256. During IKE negotiation, these algorithms ensure that the packets haven't been tampered with in transit. If an attacker modifies the negotiation parameters, the hash comparison at the receiving end will fail, causing the gateway to drop the packet and prevent a potential man-in-the-middle attack.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Diffie-Hellman (DH) exchange.
Why it's wrong here
Diffie-Hellman is used to establish shared secret keys over an insecure medium, not to verify integrity. While DH is essential for secure communication, it provides the keying material, whereas hashing algorithms are responsible for ensuring that the data being transmitted has not been altered.
- ✓
SHA-256 hashing.
Why this is correct
SHA-256 is a cryptographic hash function that verifies the integrity of the IKE negotiation packets. By computing the hash of the payload and comparing it to the received hash, the gateway can confirm that the message has arrived exactly as it was sent by the peer.
- ✗
AES-GCM encryption.
Why it's wrong here
AES-GCM is an encryption algorithm that provides both encryption and data integrity (AEAD). However, in the context of IKE negotiation, integrity is typically managed by standard hash functions like HMAC-SHA. AES-GCM is more commonly associated with the bulk data encryption phase, not initial IKE negotiation.
- ✗
Public Key Infrastructure (PKI).
Why it's wrong here
PKI is a framework for managing digital certificates and public keys, used for identity authentication. It does not perform the hashing required to verify packet-level integrity during the negotiation. Authentication ensures the peer is who they claim to be, while hashing ensures the messages are intact.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Check Point exam blueprint
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