The GATE Grind

GATE 2013 CS (CS1) – Question 23

Computer Networks · Principles of Layering · 1 mark · Multiple choice

X signs message M, encrypts the message/signature pair and sends it to Y. Which key order is used to sign/encrypt and then decrypt/verify?

  1. X private then Y private; X public then Y public
  2. X private then Y public; X public then Y private
  3. X public then Y private; Y public then X private
  4. X private then Y public; Y private then X public

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (D) X private then Y public; Y private then X public

Explanation

X signs with X’s private key and encrypts for Y with Y’s public key. Y first decrypts with Y’s private key and then verifies X’s signature using X’s public key. Therefore D. The reverse order in B cannot verify an encrypted signature before decryption.

More Principles of Layering questions

All Principles of Layering questions →