Which of the following best describes the relationship between the public key and private key in RSA?

• A. Public key encrypts; Private key decrypts
• B. Private key encrypts; Public key decrypts
• C. Both keys encrypt and decrypt
• D. Neither key is used for encryption

Answer: (A)

In RSA, a key pair is used so that the public key can be shared openly to enable others to send confidential data, while the private key remains secret to decrypt that data. The essential relationship is that data encrypted with the public key can only be decrypted with the corresponding private key, which is what gives confidentiality. The private key can also be used to create signatures, which the public key can verify to provide authenticity, but for the basic encryption/decryption flow the public key handles encryption and the private key handles decryption.