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WASM browser demo - MPF build, prove, verify

This page ports the MPF write path to WebAssembly. It mirrors the CSMT write demo, but uses mpf-write.wasm to mutate a Merkle Patricia Forest and mpf-verify.wasm to re-check Aiken-compatible proof steps against the reported root.

Try it

Open the standalone demo

What is different from CSMT

  • MPF proof bytes are the Aiken proof-step list only. The verifier also needs the query key and, for inclusion mode, the value as separate inputs.
  • Raw browser keys are routed through the same blake2b_256(key) path used by Aiken, via fromHexKVAikenHashes / aikenKeyPath, so the write and verify sides agree on the trie path.
  • Presence and absence share the same CBOR proof-step encoding. The write side distinguishes them with ptype = 0 for inclusion and ptype = 1 for exclusion.
  • An empty forest returns ptype = 0xff and no proof payload.

That matches the merged Aiken-parity exclusion-proof work: the browser transport reuses the canonical proof-step format instead of introducing a second exclusion-proof encoding.

What the demo ships

  • mpf-write.wasm - the write entry point exported via nix build .#mpf-write-wasm
  • mpf-verify.wasm - the pure Aiken-compatible verifier exported via nix build .#mpf-verify-wasm
  • index.html + write.js - the static page that runs both modules under @bjorn3/browser_wasi_shim

Workflow

  1. Insert or delete key/value pairs and watch the MPF root update.
  2. Prove a key. Present keys return the current value plus inclusion proof bytes; absent keys return an exclusion witness.
  3. Verify the proof against the root via mpf-verify.wasm.
  4. Tamper and verify to confirm the verifier rejects modified proof bytes.
  5. Reload the page and continue from the persisted IndexedDB state.

Stdin protocol

mpf-write-wasm uses the same state-and-ops envelope as the CSMT write demo:

Field Payload
slen state prior MPFInMemoryDB blob (empty to start)
n number of ops
n x op opcode-tagged: 0 klen key vlen value for insert, 1 klen key for delete
qlen queryKey key to prove or disprove

The stdout response is:

Field Payload
slen state updated MPFInMemoryDB blob
root 32-byte post-mutation root hash
vlen value queried key's value, empty if absent
ptype 1 byte: 0 inclusion, 1 exclusion, 0xff none
plen proof Aiken-compatible CBOR proof-step bytes

mpf-verify-wasm consumes a richer stdin because the proof bytes alone do not carry the query context:

Field Payload
opcode 0 inclusion or 1 exclusion
root 32-byte trusted root
klen key raw query key bytes
vlen value raw value bytes, empty for exclusion
plen proof Aiken-compatible CBOR proof-step bytes

Build it yourself

nix build .#mpf-write-wasm
nix build .#mpf-verify-wasm
nix build .#mpf-wasm-write-demo
PORT=8002 nix run .#mpf-wasm-write-demo

The result is a static directory containing index.html, write.js, mpf-write.wasm, and mpf-verify.wasm. The docs site composes that same bundle via nix build .#docs.