# Interview — Hash-linked blocks

**Q1. What problem does this mechanism solve?**
How can a verifier notice when an old transaction changes? Hash canonical block fields and verify the full chain.

**Q2. What is the naive failure mode?**
Editing a historical block invalidates its hash and every descendant hash pointer.

**Q3. Is this enough for a secure public blockchain?**
No. This lab isolates one mechanism; production needs cryptographic identities, network rules, adversarial validation, consensus and operational safeguards.

**Q4. What would you test?**
Happy path, malformed input, tampering and disagreement or competing histories where relevant.