In asymmetric cryptography, which key should be used to encrypt a message intended for the recipient?

In asymmetric cryptography, which key should be used to encrypt a message intended for the recipient?

• A. Sam's private key
• B. Sam's public key
• C. Mary's private key
• D. A symmetric session key

Answer: (B)

In asymmetric cryptography, protecting confidentiality means only the intended recipient can read the message. To achieve this, you encrypt the message with the recipient’s public key. The public key is widely available, but the private key, held only by the recipient, is needed to decrypt. Encrypting with the public key ensures that, even if someone intercepts the message, they cannot read it without the corresponding private key. Encrypting with the sender’s private key would function as a signature—anyone with the sender’s public key could decrypt it, which doesn’t keep the content secret. Using the other person’s private key isn’t feasible for encryption because private keys are not shared. A symmetric session key is part of symmetric cryptography and isn’t the mechanism used for public-key encryption. Therefore, the recipient’s public key is the correct choice.

In asymmetric cryptography, protecting confidentiality means only the intended recipient can read the message. To achieve this, you encrypt the message with the recipient’s public key. The public key is widely available, but the private key, held only by the recipient, is needed to decrypt. Encrypting with the public key ensures that, even if someone intercepts the message, they cannot read it without the corresponding private key.

Encrypting with the sender’s private key would function as a signature—anyone with the sender’s public key could decrypt it, which doesn’t keep the content secret. Using the other person’s private key isn’t feasible for encryption because private keys are not shared. A symmetric session key is part of symmetric cryptography and isn’t the mechanism used for public-key encryption. Therefore, the recipient’s public key is the correct choice.