If usera wants to send a secure message to userb using an asymmetric cryptographic algorithm, which key does userb use to decrypt the message?

userB will use his/her private key.

Explanation:

The steps involved in using asymmetric cryptographic algorithm are as follow:

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 UserA wishes to send a confidential message to UserB, UserA encrypts the message using UserB's public key.

4. When UserB receives the message, she decrypts it using her private key.