Bob wants to send Alice a file that is encrypted using public key cryptography. Which of the following statements is correct regarding the use of public key cryptography in this scenario?

In this scenario, the correct statement involves Bob using Alice's public key to encrypt the file, followed by Alice using her private key to decrypt it. This approach exemplifies the fundamental principles of public key cryptography, which is designed for secure data transmission.

When Bob encrypts a file with Alice's public key, the encryption ensures that only Alice can decrypt it, as only she possesses the corresponding private key. This mechanism allows for the confidentiality of the message, meaning that even if someone intercepts the encrypted file, they cannot decrypt it without access to Alice's private key.

In public key cryptography, each user has a pair of keys: a public key, which can be shared with anyone, and a private key, which must be kept secret. By using Alice's public key for encryption, Bob ensures that only Alice can access the file, maintaining effective control over the sharing of sensitive information.

The other options do not apply correctly to the principles of public key cryptography. For instance, using Bob's private key to encrypt data, or using Bob's private key for decryption, does not align with the standard practices of ensuring secure communication.