# provable

What gno.land can and cannot prove about itself, demonstrated rather than asserted.

Demo realm for [`p/moul/x/merkle/v0`](../../../../../p/moul/x/merkle/v0) and
[`p/moul/x/mmr/v0`](../../../../../p/moul/x/mmr/v0).

## The working half

The realm keeps a small append-only log in a Merkle mountain range and hands out inclusion
proofs against its root. Appending costs O(log n) hashes and never rebuilds. Verification is
a single native `crypto/merkle` call.

```
Append("something")                  → index
Root()                               → the current root, hex
ProofOf(index)                       → path, before, after
Verify(root, index, total, entry, path, before, after) → bool
```

`Verify` takes the root as an **argument** rather than reading it from state. That is the
honest signature: the realm is a verifier, not an oracle. Passing `Root()` checks against the
live log; passing an older root checks against that older log.

`VerifyFixed` accepts the other proof encoding, the flat Tendermint sibling list, against the
same root. Both work because the log's root **is** the Tendermint simple-tree root over the
same entries. `TestVerifyFixedAcceptsTendermintProof` pins that rather than asserting it.

## The half that is the point

A proof from this realm says *this entry is consistent with the root this realm published*.
It cannot say *this root is the chain's own*. Two independent reasons, both verifiable in the
monorepo source:

**1. Realm state is not merkleized.** `gno.land/pkg/gnoland/app.go` mounts exactly two stores:

```go
baseApp.MountStoreWithDB(mainKey, iavl.StoreConstructor, cfg.DB)      // merkleized
baseApp.MountStoreWithDB(baseKey, dbadapter.StoreConstructor, cfg.DB) // not
```

and `tm2/pkg/store/dbadapter/store.go` says it in a comment: *"Always returns a zero
commitID, as dbadapter store doesn't merkleize"*. The VM keeper takes both, and
`gnovm/pkg/gnolang/store.go` puts realm objects, types and realm metadata in the **base**
store.

| Data | Store | Provable against the app hash |
|---|---|---|
| Package source | iavl | yes |
| Account balances | iavl | yes |
| Escaped object hashes (cross-realm, refcount > 1) | iavl | yes, the hash only |
| Realm objects, types, realm metadata | base | **no** |
| This log | base | **no** |

So you can prove to a light client that a package has a given source, and that an address
holds a given balance. You cannot prove that any realm's AVL tree contains any key. Every
GRC20 balance and every DAO vote on the chain is, today, unprovable.

**2. A realm cannot see a header.** `chain/runtime` exposes `ChainID`, `ChainDomain`,
`ChainHeight` and `GetSessionInfo`, and nothing else. No app hash, no block hash, no header.
Even handed a valid Tendermint proof, a realm has no trusted root to check it against.

The one crack in the wall: an **escaped** object, one referenced across realm boundaries, does
get its hash written into the IAVL store. Cross-realm objects are partially provable already.
Nothing else is.

## Why say so out loud

Merkle proofs are the part of a chain that most invites overclaiming. "Verifiable on chain"
is true here in a narrow sense and false in the sense a reader assumes. Anything built on
Merkle proofs in a gno realm is trust-minimised relative to a committed root, never trustless.
A demo that showed only the working half would be the interesting-sounding part of a true
story.

## Bounds

`MaxEntries` is 512 and `MaxEntryLen` is 256 bytes. `Render` lists the last 10 entries, so the
page stays a fixed size: the chain caps a query at `maxGasQuery` and a reader cannot raise it,
so an unbounded `Render` is a permanently unreadable page.

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---

Part of **[moul/gno-contracts](https://github.com/moul/gno-contracts)** — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage.

**Dependency graph:**

![gno.land/r/moul/x/provable/v0 dependency graph](https://raw.githubusercontent.com/moul/gno-contracts/main/_assets/gno.land/r/moul/x/provable/v0/deps.png)

> 🧪 **Highly experimental — potentially vibe-coded.** Not audited; may break, change, or be removed at any time. Do not use with anything of value. Full disclaimer: [DISCLAIMER](https://github.com/moul/gno-contracts/blob/main/DISCLAIMER.md).

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