Protecting Confidential Documents from Eavesdropping

D.

To ensure that the confidential document is protected from eavesdropping, Joe should encrypt it using Ann's public key.

Here's why:

Encryption is the process of converting plaintext data into ciphertext, which is unreadable without the key to decrypt it. Encryption helps to protect data from unauthorized access by ensuring that only authorized users with the right decryption key can access it.

Public key encryption, also known as asymmetric encryption, involves two keys: a public key and a private key. The public key is freely available to anyone who wants to send encrypted messages to the owner of the private key. The private key is kept secret and is used by the owner to decrypt messages encrypted with their public key.

In this scenario, Joe wants to send a confidential document to Ann. To ensure that the document is protected from eavesdropping, he should encrypt it using Ann's public key. This means that only Ann, with her private key, will be able to decrypt and read the message.

Using Joe's private key (Option A) to encrypt the document would not be appropriate since Joe's private key is meant to be kept secret and should only be used for digital signatures or decryption. Anyone who intercepts the encrypted document could easily decrypt it since Joe's public key is publicly available.

Encrypting the document with Joe's public key (Option B) would not be appropriate since Joe's public key can be accessed by anyone, and encrypting the document with it would not provide any confidentiality or protection from eavesdropping.

Encrypting the document with Ann's private key (Option C) would not be appropriate since Ann's private key is meant to be kept secret and should only be used for decryption or digital signatures.

Therefore, the correct option is to encrypt the document with Ann's public key (Option D), which ensures that only Ann, with her private key, will be able to decrypt and read the message, thereby providing confidentiality and protection from eavesdropping.