If a hash digest changes after transmission, what does this indicate?

• A. Data integrity is unaffected.
• B. Data remains unchanged.
• C. Hash algorithm expired.
• D. Data integrity breach or tampering.

Answer: (D)

Hash digests act as fingerprints for data. They’re a concise representation of exactly what the data contains, so even a tiny change in the content produces a completely different hash. When data is transmitted, the receiver recalculates the hash on the received data and compares it to the hash sent with the data. If the hash changes after transmission, it means the content no longer matches the original, indicating that the data has been altered or corrupted in transit. In cybersecurity terms, this points to a breach of data integrity due to tampering or unintended modification. It doesn’t imply the data is unchanged or that the algorithm expired; it simply shows the integrity check failed. To protect against this, pair hashing with authentication mechanisms like digital signatures or HMAC so you can verify both integrity and origin.