> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lucid.foundation/llms.txt
> Use this file to discover all available pages before exploring further.

# Anchoring

> How Lucid commits epoch roots to Solana and EVM for verifiable proof

Anchoring is how Lucid makes AI interactions permanently verifiable. Cryptographic receipts are batched into epochs, compressed into a Merkle Mountain Range (MMR) root, and committed on-chain. Anyone can later verify that a specific interaction occurred without trusting Lucid.

## The Receipt-to-Chain Pipeline

```
AI interaction
  -> Receipt created (SHA-256 of RFC 8785 canonical JSON)
  -> Ed25519 signed by orchestrator
  -> Appended to MMR
  -> Epoch finalized (>100 receipts OR >1 hour)
  -> MMR root committed on-chain (Solana + EVM)
  -> Epoch bundle archived to DePIN storage
```

## Key Algorithms

### Receipt Hashing

Every receipt is hashed using SHA-256 over RFC 8785 canonical JSON (JCS). This ensures identical receipts produce identical hashes regardless of JSON key ordering or formatting.

### Merkle Mountain Range (MMR)

Receipts are appended to an MMR -- an append-only authenticated data structure. The root is computed via SHA-256 with right-to-left peak bagging.

Properties:

* Append-only (no rewriting history)
* Efficient inclusion proofs (O(log N))
* Supports batched verification

### Epoch Finalization

An epoch closes when either condition is met:

* **100+ receipts** accumulated
* **1+ hour** since epoch opened

## On-Chain Commitment

The `thought_epoch` Solana program stores MMR roots on-chain with three instruction variants:

| Instruction       | Description                                                  |
| ----------------- | ------------------------------------------------------------ |
| `commit_epoch`    | Single epoch root (32-byte MMR root)                         |
| `commit_epochs`   | Batch up to 16 roots in one transaction                      |
| `commit_epoch_v2` | Extended metadata: epoch ID, leaf count, timestamp, MMR size |

Each commitment is stored in a PDA derived from the authority's public key.

## Multi-Chain Anchoring

Lucid anchors to both Solana and EVM chains simultaneously. Configure via the `ANCHORING_CHAINS` environment variable:

```bash theme={null}
ANCHORING_CHAINS=solana-devnet,base
```

EVM anchoring uses the `EpochRegistry` contract, which stores the same root hash, epoch ID, and metadata.

## Gas Costs

| Operation                        | Cost          |
| -------------------------------- | ------------- |
| iGas (per inference call)        | 1 LUCID       |
| mGas (per epoch root commitment) | 5 LUCID       |
| Batch commit (16 roots)          | 7 LUCID total |

## DePIN Archival

After on-chain commitment, the full epoch bundle (all receipts, MMR state, metadata) is archived to decentralized storage:

| Provider   | Tier      | Use Case                                   |
| ---------- | --------- | ------------------------------------------ |
| Arweave    | Permanent | Immutable epoch bundles, passport metadata |
| Lighthouse | Evolving  | MMR checkpoints, memory snapshots          |

All DePIN uploads go through the `AnchorDispatcher`, which handles storage selection, CID tracking, and deduplication.

## Verifying a Receipt

To verify that a specific receipt was included in an anchored epoch:

```bash theme={null}
# Get an inclusion proof
curl https://api.lucid.foundation/v1/receipts/:id/proof \
  -H "Authorization: Bearer lk_..."

# Verify against on-chain root
curl -X POST https://api.lucid.foundation/v1/receipts/:id/verify \
  -H "Authorization: Bearer lk_..."
```

The proof contains the receipt hash, the MMR path, and the on-chain epoch root -- sufficient for independent verification.