ZK VM (Z-Chain)

The ZK VM (Z-Chain) is a privacy-focused virtual machine that implements zero-knowledge proofs for confidential transactions. It uses a UTXO model with nullifiers to prevent double-spending while keeping transaction details private. The Z-Chain supports multiple proof systems (Groth16, PLONK), shielded addresses, and optional FHE for encrypted computation.

VM/engine boundary. This VM is a pure block.ChainVM state machine: it parses, verifies, and applies blocks deterministically — proof verification and nullifier checks happen at block Verify. The single Quasar engine owns all consensus, gossip, and propagation — this VM ships none of its own. State is replayed from block bytes only; no wall-clock, no floating-point non-determinism, no per-node modes. See the Go-Live Standard.

Status

Go-live target for the Lux primary network (D + A + Z + B).

Architecture

• Shielded UTXO Model: Privacy-preserving UTXO transactions with nullifier tracking
• ZK Proof Verification: Groth16 and PLONK proof systems
• Private Addresses: Stealth address generation for receiver privacy
• Nullifier Database: Prevents double-spending without revealing which UTXO was spent
• State Tree: Merkle tree of commitments for membership proofs
• FHE Support: Optional BFV/CKKS encrypted computation (128/192/256-bit security)
• Mempool: Transaction pool with proof pre-verification

Configuration

{
  "enableConfidentialTransfers": true,
  "enablePrivateAddresses": true,
  "proofSystem": "groth16",
  "circuitType": "transfer",
  "verifyingKeyPath": "/path/to/vk",
  "trustedSetupPath": "/path/to/setup",
  "enableFHE": false,
  "fheScheme": "BFV",
  "securityLevel": 128,
  "maxUtxosPerBlock": 1000,
  "proofVerificationTimeout": "10s",
  "proofCacheSize": 10000
}

Key Parameters

REST API

The Z-Chain exposes three handler groups. Base endpoint:

https://api.lux.network/{network}/ext/bc/{blockchain-id}

Transaction Endpoints (/rpc)

• POST /sendTransaction -- Submit a shielded transaction with ZK proof
• GET /getTransaction -- Get transaction by ID (returns status: pending/confirmed)
• POST /createShieldedTransaction -- Create a shielded transaction (shield public funds)

Block Endpoints (/rpc)

• GET /getBlock -- Get block by ID
• GET /getLatestBlock -- Get the most recent block

UTXO Endpoints (/rpc)

• GET /getUTXO -- Get a UTXO commitment
• GET /getUTXOCount -- Get total UTXO count

Status Endpoints (/rpc)

• GET /getStatus -- Get chain status

Privacy Endpoints (/privacy)

• POST /generateAddress -- Generate a new stealth address
• GET /getAddress -- Get address details
• POST /decryptNote -- Decrypt a received note using viewing key
• GET /isNullifierSpent -- Check if a nullifier has been spent

Proof Endpoints (/proof)

• POST /generateTransferProof -- Generate a ZK proof for a transfer
• POST /generateShieldProof -- Generate a ZK proof for shielding funds
• POST /verifyProof -- Verify a ZK proof
• GET /getProofStats -- Get proof generation/verification statistics

Example: Send a Shielded Transaction

curl -X POST \
  https://api.lux.network/mainnet/ext/bc/{blockchain-id}/rpc/sendTransaction \
  -H "Content-Type: application/json" \
  -d '{
    "nullifiers": ["0x..."],
    "commitments": ["0x..."],
    "proof": "0x...",
    "encryptedData": "0x..."
  }'

Example: Check Nullifier

curl "https://api.lux.network/mainnet/ext/bc/{blockchain-id}/privacy/isNullifierSpent?nullifier=0x..."

Related LPs

See lps.lux.network for the relevant Lux Proposals governing this chain.