GATE | GATE-CS-2016 (Set 1) | Question 62

Consider that B wants to send a message m that is digitally signed to A. Let the pair of private and public keys for A and B be denoted gt20 represent the operation of encrypting m with a key Kx and H(m) represent the message digest. Which one of the following indicates the CORRECT way of sending the message m along with the digital signature to A?


(A) A
(B) B
(C) C
(D) D

Answer: (B)

Explanation: Digital signature are electronic signatures which ensures the integrity ,non repudiation and authenticity of message.Message digest is a hash value generated by applying a function on it. Message digest is encrypted using private key of sender ,so it can only be decrypted by public key of sender.This ensures that the message was sent by the known sender. Message digest is sent with the original message to the receiving end,where hash function is used on the original message and the value generated by that is matched with the message digest.This ensures the integrity and thus,that the message was not altered. Digital signature uses private key of the sender to sign digest. So option B is correct as it is encrypting digest of message H(m) using its private key K-B.

This solution is contributed by Shashank Shanker khare.

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