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Using public key cryptography, X adds a digital signature σ to message M, encrypts < M, σ > and sends it to Y, where it is decrypted. Which one of the following sequences of keys is used for the operations?
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- Encryption: X’s private key followed by Y’s private key; Decryption: X’s public key followed by Y’s private 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 public key followed by Y’s private key; Decryption: Y’s public key followed by X’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 private key followed by Y’s private key; Decryption: X’s public key followed by Y’s private key
Correct Option: D
As stated X adds a digital signature σ to message M encrypts < M, σ > and transmits it to Y. In order to the make sure that Y receives the message and is able to decrypt it the following sequences of keys is used for the operations.
(D) Encryption X’s private key followed by Y’s public key The message needs to be encrypted by the sender’s private key and receiver’s public key in order to maintain authenticity and confidentiality.
Decryption Y’s private key followed by X’s public key On receiving the encrypted message, receiver Y will have to decrypt it using his own private key and by using sender X’s public key.
