Proof Verification

Verify ZK proofs server-side before transaction submission to catch invalid proofs early and reduce failed transactions.

When to Use

•Validating proofs before submitting transactions to the network
•Building a verification gateway for incoming proofs
•Implementing batch verification for high-throughput systems
•Checking proof validity as part of an API request
•Debugging proof generation issues

Key Concepts

Why Verify Server-Side?

Benefit	Description
Fail fast	Catch invalid proofs before network submission
Save gas	Avoid transaction fees for invalid proofs
Better UX	Provide immediate feedback to users
Security	Validate proofs from untrusted clients

Verification vs Validation

•Verification - Cryptographic check that proof is valid for the circuit
•Validation - Business logic checks (e.g., correct public inputs)

typescript

// Both verification and validation
async function verifyAndValidate(proof: Proof, publicInputs: PublicInputs): Promise<boolean> {
  // Step 1: Cryptographic verification
  const isValidProof = await verifier.verify(proof, publicInputs);
  if (!isValidProof) return false;

  // Step 2: Business validation
  const isValidBusiness = validateBusinessRules(publicInputs);
  return isValidBusiness;
}

Verification Performance

Verification is much faster than proof generation:

Operation	Typical Duration
Proof Generation	5-30 seconds
Proof Verification	10-100 milliseconds

References

Document	Description
verification-api.md	Verifier SDK setup and API reference

Examples

Example	Description
pre-submit-validation/	Verify before transaction submit
batch-verification/	Verify multiple proofs in parallel

Quick Start

1. Set Up Verifier

typescript

import { createVerifier } from '@midnight-ntwrk/midnight-js-verifier';

const verifier = await createVerifier({
  verificationKeysPath: './circuit-keys',
});

2. Verify a Single Proof

typescript

async function verifyProof(
  circuitId: string,
  proof: Uint8Array,
  publicInputs: Record<string, unknown>
): Promise<boolean> {
  try {
    const result = await verifier.verify(circuitId, proof, publicInputs);
    return result.valid;
  } catch (error) {
    console.error('Verification failed:', error);
    return false;
  }
}

3. Verify Before Submit

typescript

async function submitWithVerification(
  transaction: Transaction
): Promise<string> {
  // Extract proof and public inputs from transaction
  const { proof, publicInputs, circuitId } = transaction;

  // Verify first
  const isValid = await verifyProof(circuitId, proof, publicInputs);
  if (!isValid) {
    throw new Error('Proof verification failed');
  }

  // Submit to network
  return await submitTransaction(transaction);
}

Common Patterns

Verification Gateway

typescript

import express from 'express';

const app = express();

app.post('/api/verify', async (req, res) => {
  const { circuitId, proof, publicInputs } = req.body;

  try {
    const result = await verifier.verify(
      circuitId,
      Buffer.from(proof, 'base64'),
      publicInputs
    );

    res.json({
      valid: result.valid,
      circuitId,
      verificationTime: result.duration,
    });
  } catch (error) {
    res.status(400).json({
      valid: false,
      error: error.message,
    });
  }
});

Batch Verification

typescript

interface ProofBatch {
  circuitId: string;
  proof: Uint8Array;
  publicInputs: Record<string, unknown>;
}

async function verifyBatch(
  proofs: ProofBatch[]
): Promise<Map<number, boolean>> {
  const results = new Map<number, boolean>();

  // Verify in parallel
  const verifications = proofs.map(async (p, index) => {
    try {
      const result = await verifier.verify(
        p.circuitId,
        p.proof,
        p.publicInputs
      );
      results.set(index, result.valid);
    } catch {
      results.set(index, false);
    }
  });

  await Promise.all(verifications);
  return results;
}

Caching Verified Proofs

typescript

import { createHash } from 'crypto';

const verifiedProofs = new Map<string, boolean>();

function proofHash(proof: Uint8Array, publicInputs: Record<string, unknown>): string {
  const data = JSON.stringify({ proof: proof.toString(), publicInputs });
  return createHash('sha256').update(data).digest('hex');
}

async function verifyWithCache(
  circuitId: string,
  proof: Uint8Array,
  publicInputs: Record<string, unknown>
): Promise<boolean> {
  const hash = proofHash(proof, publicInputs);

  // Check cache
  if (verifiedProofs.has(hash)) {
    return verifiedProofs.get(hash)!;
  }

  // Verify
  const result = await verifier.verify(circuitId, proof, publicInputs);
  verifiedProofs.set(hash, result.valid);

  return result.valid;
}

Verification with Timeout

typescript

async function verifyWithTimeout(
  circuitId: string,
  proof: Uint8Array,
  publicInputs: Record<string, unknown>,
  timeoutMs = 5000
): Promise<boolean> {
  const controller = new AbortController();
  const timeout = setTimeout(() => controller.abort(), timeoutMs);

  try {
    const result = await verifier.verify(circuitId, proof, publicInputs, {
      signal: controller.signal,
    });
    return result.valid;
  } catch (error) {
    if (error.name === 'AbortError') {
      throw new Error('Verification timeout');
    }
    throw error;
  } finally {
    clearTimeout(timeout);
  }
}

Error Classification

typescript

enum VerificationError {
  INVALID_PROOF = 'INVALID_PROOF',
  INVALID_PUBLIC_INPUTS = 'INVALID_PUBLIC_INPUTS',
  CIRCUIT_NOT_FOUND = 'CIRCUIT_NOT_FOUND',
  MALFORMED_PROOF = 'MALFORMED_PROOF',
  TIMEOUT = 'TIMEOUT',
}

function classifyVerificationError(error: Error): VerificationError {
  if (error.message.includes('circuit')) {
    return VerificationError.CIRCUIT_NOT_FOUND;
  }
  if (error.message.includes('public input')) {
    return VerificationError.INVALID_PUBLIC_INPUTS;
  }
  if (error.message.includes('malformed')) {
    return VerificationError.MALFORMED_PROOF;
  }
  if (error.message.includes('timeout')) {
    return VerificationError.TIMEOUT;
  }
  return VerificationError.INVALID_PROOF;
}

Performance Considerations

Concern	Mitigation
Verification key loading	Preload keys at startup
High request volume	Use verification caching
Large batches	Limit concurrent verifications
Memory usage	Stream large proof batches

Related Skills

•proof-generation - Generate proofs server-side
•proof-caching - Cache verification results
•prover-optimization - Optimize prover that creates proofs

Related Commands

None currently defined.