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The Merkle Mountain Range is an append-only data structure that powers Lucid’s receipt verification system.

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Why MMR?

FeatureStandard Merkle TreeMMR
AppendRequires rebuildO(log n)
Proof sizeO(log n)O(log n)
Append-onlyNoYes
StreamingNoYes

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How It Works

Height 3:            15
                   /    \
Height 2:        7        14
               /   \    /    \
Height 1:    3      6   10     13
            / \   / \  / \   / \
Height 0: 1   2 4   5 8  9  11  12
          R1  R2 R3 R4 R5 R6 R7  R8

Ri = Receipt i (leaf node)
Internal nodes = hash(left || right)
Each receipt is a leaf in the MMR. Internal nodes are the hash of their children. The root of the MMR is what gets anchored on Solana.

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Inclusion Proof

To prove receipt R3 is in the MMR, you need:
  1. R3’s hash (the leaf)
  2. R4’s hash (sibling)
  3. Node 3’s hash (uncle)
  4. Node 14’s hash (uncle)
This path lets anyone verify R3 is included without downloading all receipts.

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API

// Get the current MMR root
const root = await lucid.mmr.root();

// Get a receipt's inclusion proof
const proof = await lucid.receipts.proof(receiptId);

// Verify the proof
const valid = verifyMMRProof(proof.leaf, proof.path, root.hash);

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Signer

The session signer creates Ed25519 signatures for each receipt: 
const pubkey = await lucid.signer.pubkey();
// Use this to verify receipt signatures offline