Answer:
The correct answer is A: UserB sends UserA UserB's public key
Explanation:
In Asymmetrical Encryption, the both user involve in the secure communication must have a pair of key called public and private key. There are various step involves with engaging in Asymmetrical encryption, they include:
1. Each user generates a pair of keys to be used for the encryption and decryption of messages.
2. Each user places one of the two keys in a public register or other accessible file. This is the public key. The companion key is kept private.
3. If User B wishes to send a confidential message to User A, User B encrypts the message using User A's public key.
4. When User A receives the message, User A decrypts it using her private key. No other recipient can decrypt the message because only User A knows User A's private key.
Therefore, from the steps above, Option B and C are wrong because the private key/secret key should never be shared between users in asymmetrical encryption.
Option A is the correct answer as UserB sends UserA UserB's public key which is available to the everyone.
