Question 1435 – ISRO-2017 December

Using public key cryptography, X adds a digital signature σ to a message M, encrypts (M,σ) and sends it to Y, where it is decrypted. Which one of the following sequence of keys is used for operations?

Correct Answer: C

Question 4 Explanation:

Encryption: Source has to encrypt with its private key for forming Digital signature for Authentication. Source has to encrypt the (M, σ) with Y’s public key to send it confidentially.
Decryption: Destination Y has to decrypt first with its private key, then decrypt using source public key.

Encryption : X’s private key followed by Y’s private key. Decryption : X’s public key followed by Y’s public key.

Encryption : X’s private key followed by Y’s public key; Decryption : X’s public key followed by Y’s private key

Encryption : X’s private key followed by Y’s public key; Decryption : Y’s private key followed by X’s public key.

Encryption : X’s public key followed by Y’s private key; Decryption : Y’s public key followed by X’s private key.