Network Defense Essentials (NDE) Practice Exam

What objective of cryptography is achieved when a digital signature is attached to a file?

1. Confidentiality

2. Integrity

3. Authentication

4. Nonrepudiation

The correct answer is: Integrity

When a digital signature is attached to a file, it primarily ensures integrity. This means that the signature verifies that the contents of the file have not been altered in any way since the signature was applied. When the recipient receives the file and the accompanying digital signature, they can use the public key associated with the signature to check the hash of the received file against the hash value that was originally signed. If the hashes match, it confirms that the file’s contents are intact and that no unauthorized changes have occurred. While authentication and nonrepudiation are also objectives of cryptography, they serve different roles in this context. Authentication helps verify the identity of the sender, ensuring that the file comes from a legitimate source. Nonrepudiation prevents the sender from denying that they sent the file, providing proof of the origin of the document. Confidentiality, on the other hand, is focused on ensuring that the information remains private, which is not directly provided by a digital signature. Therefore, integrity is the primary objective achieved by attaching a digital signature to a file.