In public-key encryption for confidentiality, which statement is true?

• A. Encrypt with recipient's public key; decrypt with recipient's private key
• B. Encrypt with recipient's private key; decrypt with recipient's public key
• C. Encrypt with sender's private key; decrypt with sender's public key
• D. Encrypt with verifier's public key; decrypt with verifier's private key

Answer: (A)

Public-key encryption for confidentiality relies on using the recipient’s public key to protect the message so that only the recipient, who holds the corresponding private key, can decrypt it. Encrypting with the recipient’s public key ensures that the secret stays confidential and only the intended recipient can access it. Using the recipient’s private key to encrypt would allow anyone with the public key to decrypt, which defeats confidentiality and is instead used for authentication or digital signatures, not secrecy. Similarly, encrypting with the sender’s private key (and decrypting with the sender’s public key) serves to verify the sender’s identity, not to keep the content secret. Encrypting with a verifier’s public key doesn’t align with the standard confidentiality goal for a recipient in a typical message exchange. So the correct approach for confidentiality is encrypting with the recipient’s public key and decrypting with the recipient’s private key.