GATE | GATE CS 2013 | Question 13

Using public key cryptography, X adds a digital signature to message M, encrypts < M, >, and sends it to Y, where it is decrypted. Which one of the following sequences of keys is used for the operations?
(A) Encryption: X’s private key followed by Y’s private key; Decryption: X’s public key followed by Y’s public key
(B) Encryption: X’s private key followed by Y’s public key; Decryption: X’s public key followed by Y’s private key
(C) Encryption: X’s public key followed by Y’s private key; Decryption: Y’s public key followed by X’s private key
(D) Encryption: X’s private key followed by Y’s public key; Decryption: Y’s private key followed by X’s public key


Answer: (D)

Explanation: Refer http://www.facweb.iitkgp.ernet.in/~sourav/PublicKeyCrypto.pdf and http://en.wikipedia.org/wiki/Public-key_cryptography

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