In asymmetric encryption, what does the recipient use to decrypt the message?

In asymmetric encryption, the recipient uses their private key to decrypt the message. This type of encryption involves a pair of keys: a public key, which can be shared with anyone, and a private key, which is kept secret by the recipient.

When a message is encrypted using the sender's public key, only the recipient's private key can decrypt it. This ensures that only the intended recipient, who possesses the matching private key, can read the message. The security of asymmetric encryption relies on the fact that even if someone knows the sender's public key (which is openly distributed), they cannot derive the private key or decrypt the message without it.

In contrast, other options provided do not correctly describe the decryption process. The recipient's public key would not work for decryption, because it is intended for encryption. The sender's public key cannot decrypt a message, as encryption is one-way and tailored for the recipient's private key. Finally, a shared secret key pertains to symmetric encryption, where the same key is used for both encryption and decryption, making it inapplicable in the context of asymmetric encryption.