Modular Privacy Stack

// Data Layer Interface
interface DataLayer {
  store(data: EncryptedBlob): Promise<ContentHash>;
  retrieve(hash: ContentHash, key: DecryptionKey): Promise<Blob>;
  anchor(hashes: ContentHash[]): Promise<MerkleRoot>;
}

// Execution Layer Interface
interface ExecutionLayer {
  compute(input: DataReference, circuit: Circuit): Promise<Proof>;
  verify(proof: Proof): Promise<boolean>;
  getStateTransition(proof: Proof): Promise<StateTransition>;
}

// Settlement Layer Interface
interface SettlementLayer {
  escrow(asset: Asset, conditions: Outcome[]): Promise<EscrowId>;
  settle(escrowId: EscrowId, proof: Proof): Promise<TxHash>;
  revert(escrowId: EscrowId): Promise<TxHash>;
}

// Disclosure Layer Interface
interface DisclosureLayer {
  generateViewKey(scope: Scope, expiry: Timestamp): Promise<ViewKey>;
  attest(event: DisclosureEvent): Promise<AttestationId>;
  verify(viewKey: ViewKey, scope: Scope): Promise<boolean>;
}

// Encrypt bond terms
const bondData = {
  issuer: 'Bank A',
  isin: 'XS1234567890',
  principal: 10_000_000, // €10M
  coupon: 3.5,
  maturity: '2030-12-31'
};

// Generate symmetric key
const dataKey = crypto.randomBytes(32);

// Encrypt data
const encryptedBlob = await encrypt(bondData, dataKey);

// Store in Data layer
const contentHash = await dataLayer.store(encryptedBlob);

// Wrap key to threshold authorities
const wrappedKey = await thresholdKMS.wrap(dataKey, [
  authority1_pubkey,
  authority2_pubkey,
  authority3_pubkey
]);

// Store metadata on-chain
await dataCommitContract.commit(contentHash, wrappedKey);

// Investor eligibility check via ZK proof
const eligibilityCircuit = {
  inputs: {
    investorKYC: privateInput,  // Not revealed
    jurisdiction: 'DE',
    accreditedStatus: true
  },
  outputs: {
    isEligible: publicOutput  // Only this is revealed
  }
};

// Generate proof
const proof = await executionLayer.compute(
  contentHash,  // Reference to encrypted data
  eligibilityCircuit
);

// Proof attests: "Investor meets eligibility criteria"
// without revealing investor identity or KYC details

// Settlement contract verifies proof and executes transfer
function settleWithProof(
  bytes32 tradeId,
  bytes32 contentHash,
  bytes calldata executionProof
) external {
  // Verify execution proof
  require(
    executionLayer.verify(executionProof),
    "Invalid execution proof"
  );
  
  // Extract state transition
  StateTransition memory transition = 
    executionLayer.getStateTransition(executionProof);
  
  // Execute atomic DvP via ERC-7573
  bondToken.transferFrom(
    transition.from,
    transition.to,
    transition.bondAmount
  );
  
  cashToken.settleConditional(
    transition.cashOutcomeKey
  );
  
  emit SettledWithProof(tradeId, contentHash);
}

// Regulator requests access to bond terms
const disclosureRequest = {
  requestor: 'BaFin',
  scope: {
    isin: 'XS1234567890',
    dateRange: ['2026-01-01', '2026-01-31']
  },
  expiry: Date.now() + 24 * 60 * 60 * 1000  // 24 hours
};

// Policy engine verifies mandate
const approved = await policyEngine.evaluate(disclosureRequest);

if (approved) {
  // Generate time-limited view key
  const viewKey = await disclosureLayer.generateViewKey(
    disclosureRequest.scope,
    disclosureRequest.expiry
  );
  
  // Log disclosure via EAS
  const attestation = await disclosureLayer.attest({
    requestor: 'BaFin',
    dataHash: contentHash,
    viewKeyHash: hash(viewKey),
    timestamp: Date.now(),
    expiry: disclosureRequest.expiry
  });
  
  // Deliver view key to regulator
  await sendToRegulator(viewKey, attestation);
}

const auditEntry = {
  tradeId: '0xabc123...',
  layers: {
    data: {
      contentHash: '0x7f3a...',
      storageBackend: 'IPFS',
      encryptionAlgo: 'AES-256-GCM'
    },
    execution: {
      proofHash: '0x9c2e...',
      backend: 'Aztec',
      circuitId: 'eligibility-v1.2'
    },
    settlement: {
      txHash: '0xdef456...',
      chain: 'Ethereum L1',
      blockNumber: 18_456_789
    },
    disclosure: {
      attestationId: '0x3b7f...',
      requestor: 'BaFin',
      viewKeyExpiry: 1735689600
    }
  },
  timestamp: Date.now()
};

await auditLog.append(auditEntry);

{
  "isin": "XS1234567890",
  "issuer": "Bank A",
  "principal": 10000000,
  "investors": [
    {"id": "investor-1", "allocation": 5000000},
    {"id": "investor-2", "allocation": 5000000}
  ]
}

fn allocate_bonds(
  bond_data: EncryptedData,
  investor_kyc: PrivateInput
) -> pub AllocationProof {
  // Verify investor eligibility (private)
  assert(investor_kyc.accredited == true);
  assert(investor_kyc.jurisdiction == "DE");
  
  // Compute allocation (private)
  let allocation = calculate_pro_rata(bond_data, investor_kyc.id);
  
  // Output proof of valid allocation
  AllocationProof {
    is_eligible: true,
    allocation_valid: true
    // Amounts and identities remain private
  }
}

// Bond tokens transfer to buyer
bondToken.transferFrom(issuer, buyer, bondAmount);

// Payment token transfers to seller
cashToken.transferFrom(buyer, issuer, paymentAmount);

// Both succeed or both revert

// Generate view key for specific bond issuance
const viewKey = await thresholdKMS.generateViewKey({
  scope: { isin: 'XS1234567890' },
  expiry: Date.now() + 24 * 60 * 60 * 1000
});

// Attest disclosure event via EAS
const attestation = await eas.attest({
  schema: DISCLOSURE_SCHEMA,
  data: {
    dataHash: '0x7f3a...',
    requestor: 'BaFin',
    viewKeyHash: hash(viewKey),
    expiry: viewKey.expiry
  }
});