Turnkey Electronic Signature Verification System for Your Website

Typical situation: you conclude a contract with a counterparty via electronic document exchange, but they doubt the authenticity of the signature. Or you need to give clients the ability to validate a signed document online. We solve this task: from integrating a simple electronic signature to cryptographic validation of a qualified electronic signature (QES) via CryptoPro.

What problems does the verification system solve?

Different signature types — different validation logic. A simple electronic signature (drawn signature, SMS code) carries no cryptographic protection. The only way to verify its authenticity is to ensure the document has not been altered after signing. To do this, we store the document hash (SHA-256) at the moment of signing and compare it during validation. If the hashes do not match — the document has been changed, the signature is invalid.

A qualified electronic signature (QES) requires a much more complex validation. You need to decrypt the signature, verify the certificate, trust chain, validity period, and revocation status. This involves working with cryptographic providers (CryptoPro), browser plugins, or server-side SOAP calls.

Browser and device compatibility. Client-side QES validation requires installing a Browser Plugin, which is not always possible (mobile devices, corporate restrictions). Therefore, we offer server-side validation via the CryptoPro Web Service — the user simply uploads the document and signature, and all cryptography is performed on the server. This is a universal solution.

Security and logging. It is important not only to validate the signature but also to preserve proof of validation. We log every attempt: IP, User-Agent, timestamp, result. This protects against replay attacks and provides an audit trail.

How we do it?

Solution architecture

• Frontend: React 18 (Next.js 14) for the public verification page, TypeScript, Tailwind.
• Backend: Laravel 11 (PHP 8.3) or Node.js (Express) for the API and server-side validation.
• Database: PostgreSQL for storing hashes and logs, Redis for caching certificate statuses.
• Cryptography: CryptoPro CSP (server-side validation via SOAP) and CryptoPro Browser Plugin (client-side).

Client-side QES validation via the plugin is already ready and used in projects:

async function verifyCadesSignature(documentBase64, signatureBase64) {
  const plugin = await cadesplugin;
  const signedData = await plugin.CreateObjectAsync('CAdESCOM.CadesSignedData');

  await signedData.propset_ContentEncoding(plugin.CADESCOM_BASE64_TO_BINARY);
  await signedData.propset_Content(documentBase64);

  try {
    await signedData.VerifyCades(
      signatureBase64,
      plugin.CADESCOM_CADES_BES,
      true
    );
  } catch (e) {
    return { valid: false, error: e.message };
  }

  const signers = await signedData.Signers;
  const signer = await signers.Item(1);
  const cert = await signer.Certificate;

  return {
    valid: true,
    signer: {
      name: await cert.GetInfo(plugin.CAPICOM_CERT_INFO_SUBJECT_SIMPLE_NAME),
      issuer: await cert.GetInfo(plugin.CAPICOM_CERT_INFO_ISSUER_SIMPLE_NAME),
      validFrom: await cert.ValidFromDate,
      validTo: await cert.ValidToDate,
      thumbprint: await cert.Thumbprint,
    },
    signedAt: await signer.SigningTime,
    certValid: await cert.IsValid().Result,
  };
}

Server-side validation via CryptoPro Web Service — example in PHP:

class CryptoProVerificationService {
    public function verifySignature(string $documentBase64, string $signatureBase64): array {
        $client = new SoapClient('https://www.cryptopro.ru/ocsp/ocsp.php?wsdl');

        $result = $client->VerifyHash([
            'Signature' => $signatureBase64,
            'Content'   => $documentBase64,
            'Type'      => 'CAdES-BES',
            'IsDetached' => true,
        ]);

        return [
            'valid'      => $result->IsValid,
            'signerName' => $result->SignerName,
            'signedAt'   => $result->SigningTime,
            'certSerial' => $result->CertSerialNumber,
        ];
    }
}

Why is server-side validation better for the user?

Server-side validation requires no plugin installation, works on any device and browser. Validation takes 2-3 seconds — 2 times faster than installing and configuring the plugin. This reduces support requests and increases validation conversion. According to our experience, server-side validation reduces support tickets by 40%.

How does a public page and QR code simplify verification?

For external users (a counterparty verifying a contract), we create a page without authentication. Example React component:

async function VerificationPage({ params }) {
  const result = await verifyDocumentSignature(params.documentId, params.signatureId);

  return (
    <div className="max-w-2xl mx-auto p-8">
      <div className={`rounded-xl p-6 ${result.valid ? 'bg-green-50' : 'bg-red-50'}`}>
        <div className="flex items-center gap-3">
          {result.valid ? <CheckCircleIcon className="text-green-600 w-8" /> : <XCircleIcon className="text-red-600 w-8" />}
          <h1 className="text-xl font-bold">
            {result.valid ? 'Signature is valid' : 'Signature is invalid'}
          </h1>
        </div>

        {result.valid && (
          <dl className="mt-4 grid grid-cols-2 gap-4 text-sm">
            <div><dt className="text-gray-500">Signer</dt><dd>{result.signerName}</dd></div>
            <div><dt className="text-gray-500">Signing date</dt><dd>{formatDate(result.signedAt)}</dd></div>
            <div><dt className="text-gray-500">Document unchanged</dt><dd>Yes</dd></div>
            <div><dt className="text-gray-500">Certificate</dt><dd>{result.certSerial}</dd></div>
          </dl>
        )}
      </div>
    </div>
  );
}

QR code placed on the signed document leads to the verification page:

import QRCode from 'qrcode';

const verificationUrl = `${process.env.APP_URL}/verify/${documentId}/${signatureId}`;
const qrDataUrl = await QRCode.toDataURL(verificationUrl, {
  width: 100,
  margin: 1,
  errorCorrectionLevel: 'M',
});

Comparison of verification methods

Work process

1. Analysis — identify signature types, security requirements, user flow.
2. Design — choose architecture (client/server validation), stack, protocols.
3. Development — implement API, public page, QR code, integration with your CRM/ERP.
4. Testing — verify on different browsers, with real certificates, load testing.
5. Deployment — set up CI/CD, monitoring, caching.
6. Training and support — hand over documentation, access rights, conduct employee training. Provide 1 month of free support.

What is included in the work

• Source code of the verification system.
• API documentation (OpenAPI/Swagger).
• Operating instructions for administrators.
• Access to the repository and server.
• 1 month of support after launch.

Typical mistakes during implementation

• Certificate expiration is not checked — the signature could be created with an expired certificate. We always verify ValidFrom/ValidTo.
• Missing logging of verification attempts — difficult to prove that verification was performed. We log every attempt.
• QR code leads to HTTP, not HTTPS — signature data is transmitted in plain text. We use only HTTPS with HSTS.
• CORS not configured — public page fails to load due to browser restrictions. We configure headers correctly.

Timeframes and cost

Hash-based verification with public page and QR code — 2–3 days starting from $2,000. QES verification via browser plugin — 3–4 days starting from $3,000. Server-side verification via CryptoPro Web Service — 3–5 days starting from $4,500. We will provide an accurate estimate after auditing your project.

We comply with the Federal Law on Electronic Signatures (No. 63-FZ) and ensure legal validity.

Our system supports online document signing and verification, making it easy for end-users. Contact us to discuss the details. Order the development of a signature verification system — we will evaluate the project within one business day.

Web Application Security: HTTPS, CSP, XSS, CSRF, WAF, DDoS Protection

A website breach rarely looks like in movies. More often it's: a bot finds an unprotected /admin/export endpoint, downloads the customer database, and closes the connection. Or: through an outdated WordPress plugin, a web shell is uploaded, and the server starts sending spam. Or quieter: an XSS in a comment field allows stealing admin session cookies, unnoticed for months. We have analyzed dozens of such cases — each vulnerability could have been fixed at the development or audit stage.

Web application security is not a single setting. It's layers of protection, each closing a separate class of attacks. Order an audit — we'll assess the project and deliver a turnkey plan within 2–4 weeks.

How do we ensure comprehensive web application security?

HTTPS and Proper TLS Configuration

HTTPS is the minimum mandatory level. But having an SSL certificate and having a properly configured TLS are different things.

In Nginx/Apache configuration we check:

• Protocols: only TLS 1.2 and TLS 1.3, SSLv3 and TLS 1.0/1.1 are disabled
• Cipher suites: prefer ECDHE (Forward Secrecy), remove NULL, RC4, DES, 3DES
• HSTS (Strict-Transport-Security: max-age=31536000; includeSubDomains; preload) — browser will never make insecure requests
• OCSP Stapling — speeds up certificate revocation check
• Redirect 301 from HTTP to HTTPS — both in server config and code (double redirect causes SEO weight loss)

Check: SSL Labs (ssllabs.com/ssltest) should show A or A+. If B, the configuration is weak.

Let's Encrypt + Certbot for production is standard. Automatic renewal via certbot renew in cron. Wildcard certificates for subdomains via DNS-01 challenge.

Content Security Policy: The Most Powerful and Complex Protection

CSP is an HTTP header that tells the browser which sources are allowed to load resources. A properly configured CSP completely blocks most XSS attacks, even if the vulnerability exists in the code.

The problem: breaking the site with an incorrect CSP is easy. default-src 'none' — and fonts, images, JS stop working. So we start with Content-Security-Policy-Report-Only — CSP logs violations but does not block anything. We monitor reports for 2–4 weeks, refine the policy, then switch to enforcement mode.

Example of a real policy for a site with Google Analytics, Google Fonts, and Stripe:

Content-Security-Policy:
  default-src 'self';
  script-src 'self' https://www.googletagmanager.com https://js.stripe.com 'nonce-{random}';
  style-src 'self' https://fonts.googleapis.com 'unsafe-inline';
  font-src 'self' https://fonts.gstatic.com;
  frame-src https://js.stripe.com;
  img-src 'self' data: https://www.google-analytics.com;
  connect-src 'self' https://api.stripe.com https://www.google-analytics.com;
  report-uri /csp-report;

nonce — a random string generated server-side per request. Inline scripts with the correct nonce are allowed; without nonce, they are blocked. This completely breaks XSS via <script>alert(1)</script>.

'unsafe-inline' in style-src is a compromise for inline styles. It's better to remove it by moving all styles to CSS files, but that requires refactoring.

Why XSS Remains the Most Common Vulnerability?

XSS (Cross-Site Scripting) — injection of JS code through user input. According to OWASP, XSS is in the top 3 web application vulnerabilities. Three types:

Protection: never insert user input into HTML without escaping. In PHP — htmlspecialchars() with ENT_QUOTES. In Laravel Blade templates — {{ $var }} is safe, {!! $var !!} is dangerous. In React — {variable} is safe, dangerouslySetInnerHTML is dangerous. For Rich Text — use htmlpurifier on PHP or DOMPurify in the browser.

CSRF: Protecting Forms and APIs

CSRF (Cross-Site Request Forgery) — an attacker forces the victim's browser to send a request on their behalf. Example: a user is logged into a bank, opens a malicious page, which makes fetch('https://bank.ru/transfer?to=evil&amount=50000') — if the bank is unprotected, money is transferred.

CSRF tokens — standard protection for forms: the server generates a random token, stores it in the session, and inserts it as a hidden field in the form. On POST request, the token is verified. The attacker does not know the token. Laravel does this automatically with @csrf.

SameSite cookies — modern protection: SameSite=Strict or SameSite=Lax prevents the browser from sending cookies in cross-site requests. Works in all modern browsers.

API without sessions (JWT, Bearer tokens) — CSRF is irrelevant if the token is not stored in a cookie (but in the Authorization header or localStorage). However, localStorage is vulnerable to XSS — so for sensitive data, HttpOnly cookies with SameSite are preferable.

WAF and DDoS Protection

WAF (Web Application Firewall) filters HTTP traffic for attacks: SQL injection, XSS, path traversal, known exploit patterns. Options:

• Cloudflare WAF — cloud-based, OWASP Top 10 rules out of the box, custom rules via expressions. Managed Rules automatically block new threats.
• ModSecurity (Nginx/Apache) — self-hosted, OWASP Core Rule Set (CRS). Flexible but requires tuning and monitoring of false positives.
• AWS WAF — for infrastructure on AWS, integrates with CloudFront and ALB.

DDoS protection. Cloudflare at L3/L4/L7 is the de facto standard for most sites. Automatic mitigation of volumetric attacks, Under Attack Mode during active attacks. For critical infrastructure — Cloudflare Magic Transit or specialized solutions (Qrator, StormWall for the Russian market).

Rate Limiting at the application level — an additional layer. Laravel ThrottleRequests middleware: 60 requests per minute per IP for general endpoints, 5 for /login and /password/reset. Redis as a counter store — mandatory for horizontally scalable systems (otherwise limits are not synchronized between servers).

Other Mandatory Measures

Security headers. Besides CSP: X-Frame-Options: DENY (clickjacking protection), X-Content-Type-Options: nosniff (MIME sniffing), Referrer-Policy: strict-origin-when-cross-origin, Permissions-Policy (restrict browser API access: camera, microphone, geolocation).

SQL injection. Prepared statements everywhere. No concatenation of user input into SQL strings. ORM (Eloquent, Doctrine) protects by default. $wpdb->prepare() in WordPress is mandatory.

Dependency updates. composer audit and npm audit in CI/CD pipeline. Dependabot or Renovate for automatic PRs with updates. Critical CVEs — patch within 24 hours.

Secrets and configuration. .env — never in Git. Secrets in production — via CI/CD environment variables (GitHub Secrets, GitLab CI Variables) or HashiCorp Vault. Leak detection: git-secrets, truffleHog in pre-commit hooks.

How We Work

1. Audit — code scanning, configuration review, dependency analysis, manual business logic verification.
2. Planning — vulnerability remediation plan, stack selection (CSP, WAF, rate limiting).
3. Implementation — TLS setup, CSP configuration, headers, Rate Limiting, WAF.
4. Testing — re-penetration test, load testing, false positive check.
5. Deployment and Monitoring — enable production CSP, set up alerts, train the team.

What's Included

• Report with found vulnerabilities and recommendations (PDF + code snippets)
• Ready TLS configuration (Nginx/Apache)
• CSP policy with Report-Only and production versions
• WAF and Rate Limiting setup
• Dependency update plan
• Access to monitoring tools (Sentry, Datadog)
• 30 days of post-audit support (consultations, fixes)

Timeline and Cost

The budget is calculated individually — contact us for a project evaluation.