The GATE Grind

GATE 2014 CS (CS2) – Question 37

Computer Networks · Principles of Layering · 2 marks · Multiple choice

Q reaches HTTP server H through Q—R1—R2—R3—H and downloads a file. DES shared-key encryption is at session layer. I1: Downloaded file URL; I2: TCP ports at Q and H; I3: IP addresses of Q and H; I4: Link-layer addresses of Q and H. What can an intruder learn by sniffing at R2 alone?

  1. Only I1 and I2
  2. Only I1
  3. Only I2 and I3
  4. Only I3 and I4

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Correct answer: (C) Only I2 and I3

Explanation

Session-layer encryption hides application data including the requested URL. TCP ports and source/destination IP addresses remain in their unencrypted headers. Link-layer addresses at R2 belong to its adjacent links, not necessarily the end hosts. Thus **I2 and I3 only,C**.