A sender wants to send a confidential message to a recipient using public-key encryption. Which key should encrypt the message, according to the lesson?

### Why this is right The sender encrypts the message with the destination’s public key. The recipient then uses the corresponding private key to decrypt it, so the private key does not need to be sent to the sender. ### The concept A public-key pair contains a public key that can be shared and a private key that its owner keeps secret. This encryption arrangement provides confidentiality for the recipient because the corresponding private key is needed to recover the message. It is different from a digital signature, where the signer’s private key is used to sign and the corresponding public key is used to verify. ### The other options - **B. The sender’s public key**: This would not let the recipient decrypt the message unless the recipient had the sender’s corresponding private key. - **C. The recipient’s private key, which is placed in a public register**: The private key must remain secret; publishing it would defeat the purpose of the key pair. - **D. A certificate authority’s session key**: A certificate authority issues certificates; its session key is not the key specified for encrypting this message. ### Terms - **Public key**: A shareable key used in public-key cryptography. - **Private key**: The secret key corresponding to a public key. - **Confidentiality**: Preventing unauthorized people from reading information. ### Remember For confidentiality, encrypt to the recipient with the recipient’s public key.