What is a checksum and how is it used to ensure data integrity in transfers?

• A. A hash or checksum verifies content integrity by comparing a calculated value before and after transfer.
• B. It compresses data to reduce size.
• C. It replaces encryption for security.
• D. It schedules backups.

Answer: (A)

A checksum is a small value derived from the data that lets you verify its integrity after transfer. You compute this value from the original data before sending it, and send both the data and the checksum. When the data arrives, you recompute the checksum from what you received and compare it to the original. If they match, the data most likely arrived without changes; if they don’t, something altered the data during transit, so you can request a retransmission or error correction. This approach works with techniques like CRCs or cryptographic hashes, and it’s specifically about detecting accidental or corrupted changes, not about making data smaller, replacing encryption for security, or handling backups.