Block Hash Chain: Tamper Cascade & Proof-of-Work

Blockchain

Chain valid

Mining difficulty (leading zero hex digits) 2

Selected block data

Selected block

Data— Nonce— Prev-hash reference (stored)— Predecessor's actual hash— This block's hash—

Chain integrity

5 / 5

Total nonce tries

How it works

Each block stores data, a nonce, and the fixed hash of the block before it (prevHashRef) — captured permanently the moment it was mined. Its own hash is a deterministic mixing function of all three:

hash = H(index, data, nonce, prevHashRef)
valid  ⇔  hash starts with D zero hex digits   (proof-of-work)
linked ⇔  prevHashRef === H(block[i-1])         (chain integrity)

The demo hash here is a fast 64-bit avalanche mix (two Murmur-style passes), not literal SHA-256 — but it reproduces the property that matters: flipping one character of data scrambles the entire output unpredictably, so there is no shortcut to finding a matching hash except trying nonces one by one.

Tamper — editing a block's data recomputes its hash instantly. The new hash almost never still has D leading zeros, so the block turns red (proof-of-work broken). Every later block still points at the block's old hash, so they turn orange (link broken) even though their own proof-of-work is still technically valid.
Re-mine From Here — starting at the selected block, re-links prevHashRef to the predecessor's real current hash and searches nonces until a valid hash is found, then repeats for every block after it — exactly the work an attacker (or an honest miner extending a reorg) must redo.
Difficulty — each extra leading zero multiplies the average nonce search by 16×, mirroring how Bitcoin's target adjusts mining cost.
Add Block — appends a new block referencing the chain's current tip and mines it in place.

Valid & linked Proof-of-work broken Link broken Mining…

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.