GATE CSE 2016 Set 2 | Question: 23

Question

Anarkali digitally signs a message and sends it to Salim. Verification of the signature by Salim requires.

• A. Anarkali's public key.
• B. Salim's public key.
• C. Salim's private key.
• D. Anarkali's private key.

Comments

This topic is not in syllabus of GATE 2021 as it comes under network security: digital signatures and certificates

Source: https://gatecse.in/gate-2021-syllabus-including-changes/

Answer 1

In digital signature,
Alice/Anarkali/sender :P
First encrypts with own private key then again encrypts with Receivers/Bob/Salim's Public key.

Thus to decrypt, receiver will need sender's/Anarkali's public key after decrypting it with own/receiver's private key.

So, answer is A.

Comments

Alice = Anarkali :P (Y)

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https://en.wikipedia.org/wiki/Public-key_cryptography

https://en.wikipedia.org/wiki/Digital_signature

• Digital signatures, in which a message is signed with the sender's private key and can be verified by anyone who has access to the sender's public key. This verification proves that the sender had access to the private key, and therefore is likely to be the person associated with the public key. This also ensures that the message has not been tampered with, as a signature is mathematically bound to the message it originally was made with, and verification will fail for practically any other message, no matter how similar to the original message.
• In the above example the message is only digitally signed and not encrypted. 1) Alice signs a message with her private key. 2) Bob can verify that Alice sent the message and that the message has not been modified.

Answer 2

Basically it is about the authentication of the signature. How will Salim know that  Anarkali's signature is genuine? So he uses the public key of Anarkali to decrypt the message .If it works, Salim is convinced that Anarkali is the genuine sender who used her private key to encrypt the message.Hence A (ans)

Answer 3

Answer is : (a)  Anarkali's public key

There is a another concept through which this problem can be solved:

in RSA,                                                                                              

Encryption:Done by Receiver's Public key

Decryption:Done by Receiver's Private key

in Digital signature,                         

Encryption:Done by sender's private key

Decryption:Done by sender's public key

Answer 4

In digital signature, sender encrypts the message using her private key and receiver decrypts it using sender's public key.
So, option A is apt.