In what way does a hash provide a better message integrity check than a checksum (such as the Internet checksum)?
Try an answer before revealing the guidance below.
Key Concepts
- Internet checksum
- Cryptographic hash
- Collision resistance
- Deliberate modification
Answer Approach
- Ask how easy it is to find a different message with the same checksum.
- Compare with the properties of a cryptographic hash.
- Relate this to accidental errors versus deliberate tampering.
Full Answer
Answer status: Verified against study notes. Revision notes, not an official marking scheme.
The Internet checksum is designed to catch accidental errors, and it is easy to construct a different message with the same checksum (e.g. by rearranging or compensating 16-bit words), so an attacker can alter a message without detection. A cryptographic hash (such as MD5 or SHA) is computationally infeasible to invert or to find collisions for, and any small change produces a completely different digest, so it is far better at detecting deliberate modification (especially when keyed as a MAC or signed).
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