Which cryptographic service lets a receiver detect whether data was modified after it was sent?

• A. Confidentiality
• B. Integrity
• C. Authentication
• D. Non-repudiation

Answer: (B)

Integrity is the service that ensures data hasn’t been altered after it was sent. To detect any changes, the receiver verifies a value tied to the message, such as a MAC or a digital signature. With a MAC, the sender and receiver share a secret key and the sender attaches a MAC computed from the data; the receiver recomputes the MAC and checks for a match. If any modification occurs, the MAC won’t align, signaling tampering. Digital signatures work similarly by signing a hash of the message with a private key so others with the public key can verify it; tampering alters the hash and breaks verification. Confidentiality protects secrecy, authentication proves who sent the data, and non-repudiation ensures the sender can’t deny sending it, but the mechanism that reveals whether data was modified is integrity.