📝 Application layer security protocols (6 MCQs)
📖 From Data Communication and Networks • 32. Internet Security • 6 questions available
What is Application layer security protocols?
Application layer security protocols operate at the highest OSI layer to provide end-to-end security for specific applications, ensuring that data remains protected even when passing through untrusted intermediate networks or proxies.
📝 All Application layer security protocols MCQs
Q1. Which statement accurately describes IPSec transport mode?
📖 Explanation: Transport mode inserts the IPSec header and trailer around the data received from the transport layer, then the original IP header is placed afterward. Consequently, only the transport‑layer payload is encrypted or authenticated, while the original IP header remains visible. This matches the definition given in the standard.
Q2. If an attacker can modify the outer IP header in a transport‑mode IPSec packet, which consequence is most likely?
📖 Explanation: In transport mode the outer IP header is not covered by IPSec integrity checks, so an adversary can alter fields such as the destination address. Because authentication applies only to the payload, the modification is not detected, allowing the packet to be redirected without triggering a drop.
Q3. Compare transport mode and tunnel mode in terms of the network layers they protect. Which statement is correct?
📖 Explanation: Tunnel mode encapsulates the whole original IP packet—header plus payload—within a new IP header and then applies ESP or AH, so both the original header and data are protected. Transport mode, by contrast, leaves the original IP header untouched and secures only the payload. Therefore the statement in option D correctly captures the layer‑level protection differences.
Q4. A host behind a NAT wants to communicate with a remote server over the public Internet. Which IPSec mode should be used to ensure confidentiality of both payload and original IP headers, and why?
📖 Explanation: When a host behind NAT communicates across the Internet, the original source address is replaced by the NAT’s public address, and the internal IP header may reveal private topology. Tunnel mode wraps the entire original packet, including its private header, inside a new outer header, providing confidentiality for both payload and original header.
Q5. Assume a standard IPv4 header is 20 bytes and an IPSec ESP trailer adds 24 bytes in tunnel mode. If the original packet payload is 500 bytes, what is the total size of the transmitted packet after IPSec processing?
📖 Explanation: The original packet consists of a 20‑byte IPv4 header and a 500‑byte payload, totaling 520 bytes. IPSec ESP adds a 24‑byte trailer, bringing the size to 544 bytes. Tunnel mode then adds a new 20‑byte IP header, resulting in a final transmitted size of 564 bytes.
Q6. A company needs to secure communication between its remote branch office and the central data center over the public Internet. Which IPSec mode provides the strongest defense against traffic analysis and why?
📖 Explanation: Traffic analysis can infer communication patterns from observable header fields. Tunnel mode encrypts the entire original IP header along with the payload, hiding source, destination, and protocol information from eavesdroppers. Transport mode leaves the original IP header exposed, making it vulnerable to analysis. Hence tunnel mode offers the strongest protection against traffic‑analysis attacks.