GATE CS 2016 Set 1 — Question 62
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Computer Networks → Application Layer → Digital Signatures & Certificates
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Question
Consider that B wants to send a message that is digitally signed to A. Let the pair of private and public keys for A and B be denoted by and for , respectively. Let represent the operation of encrypting with a key and represent the message digest. Which one of the following indicates the CORRECT way of sending the message along with the digital signature to A?
Correct answer
(B) \m, K_B^-(H(m))\
Solution
A digital signature is used to provide authentication and non-repudiation. It is created by the sender (B) by first computing a hash (message digest) of the message , denoted as , and then encrypting this digest with the sender's private key, . The resulting signature is then sent along with the original message . Therefore, the correct format is .
- Option (A) is incorrect because it uses the sender's public key, which anyone can use and thus does not provide authentication.
- Option (C) is incorrect because it uses the receiver's private key, which the sender (B) does not possess.
- Option (D) is incorrect because it encrypts the message with the receiver's public key, which provides confidentiality but does not serve as a digital signature for authentication.
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