SSC IMD SA 2017 – Question 162

Which of the following two protocols are defined by IPsec?

• AH; SSL
• PGP; ESP
• AH; ESP
• All options are correct

Detailed Explanation:

The correct answer is c) AH; ESP.

IPsec (Internet Protocol Security) is a suite of open standards operating at the Network Layer (Layer 3) to secure IP communications. IPsec defines two primary security protocols:

1. AH (Authentication Header – IP Protocol 51): Provides data origin authentication, data integrity, and anti-replay protection for IP packets. However, AH does not provide data confidentiality (it does not encrypt data).
2. ESP (Encapsulating Security Payload – IP Protocol 50): Provides data confidentiality (encryption), along with optional origin authentication, data integrity, and anti-replay protection.

Both protocols can be operated in Transport Mode (payload secured, original IP header exposed) or Tunnel Mode (entire original IP packet encapsulated inside a new IP header).

Why Other Options are Incorrect:

• SSL (Secure Sockets Layer): Operates at the Transport/Application layer, not defined by IPsec.
• PGP (Pretty Good Privacy): An application-layer encryption protocol used for emails.