SSL/TLS Checker

• What This Tool Does

SSL/TLS Checker analyzes your website's SSL/TLS certificate and connection security, verifying encryption strength, certificate validity, expiration dates, and configuration issues.

• Why It Matters

• → Security: Encrypts data between users and your server
• → Trust: Browsers show warnings for invalid or expired certificates
• → SEO: Google penalizes sites without HTTPS
• → Compliance: Required for PCI-DSS and many privacy regulations

• How to Read the Results

• ✓ Certificate Validity: Check "Valid From" and "Valid To" dates
• ✓ Common Name: Should match your domain name
• ✓ Issuer: Certificate Authority that signed the certificate
• ✓ Protocol Version: TLS 1.2 or 1.3 recommended (avoid TLS 1.0/1.1)

• Technical Background

TLS (Transport Layer Security, RFC 8446) establishes encrypted communication channels using a multi-step handshake: (1) Client Hello — client sends supported TLS versions and cipher suites; (2) Server Hello — server selects version and cipher, sends certificate; (3) Certificate verification — client validates the certificate chain against trusted CAs; (4) Key Exchange — ECDHE or DHE generates a shared secret; (5) Session keys derived; (6) Encrypted data transfer begins. X.509 certificates (RFC 5280) contain the Subject, Issuer (CA), validity period, public key, Subject Alternative Names (SANs), and digital signature. Certificate chains must be complete: leaf certificate → intermediate CA(s) → root CA. Incomplete chains cause "unable to verify certificate chain" errors. TLS versions: TLS 1.0 and 1.1 are deprecated (RFC 8996) — browsers removed support in 2020. TLS 1.2 remains widely supported but TLS 1.3 is preferred for performance (1-RTT handshake vs 2-RTT in 1.2) and forward secrecy (all cipher suites use ephemeral keys). Certificate types: Domain Validated (DV) — automated domain ownership check only; Organization Validated (OV) — vets company identity; Extended Validation (EV) — rigorous vetting for financial/legal entities. Free DV certificates from Let's Encrypt, ZeroSSL, and Google Trust Services have made HTTPS universal. Common SSL/TLS vulnerabilities include: expired or soon-to-expire certificates (monitor expiry < 30 days), self-signed certificates not trusted by browsers, certificate/domain name mismatch (CN or SAN doesn't match the URL), weak cipher suites (RC4, 3DES, NULL, EXPORT ciphers), and outdated protocols. Security headers like HSTS (HTTP Strict Transport Security, RFC 6797) enforce HTTPS at the browser level. Certificate Transparency (RFC 9162) logs all issued certificates publicly, enabling detection of unauthorized certificate issuance for your domain. Security professionals use automated certificate monitoring to prevent unexpected expirations. Lets Encrypt certificates expire every 90 days and require automated renewal via ACME protocol clients like Certbot or acme.sh. Commercial CAs issue 1-year certificates (2-year was deprecated by browsers in 2020). OCSP (Online Certificate Status Protocol, RFC 6960) allows real-time revocation checking without downloading full CRLs. OCSP Stapling improves performance by having the server pre-fetch and cache the OCSP response. Organizations managing many certificates should use a certificate lifecycle management (CLM) platform to track expiry dates, automate renewals, and ensure consistent security configurations across all endpoints. Administrators should routinely test SSL/TLS configuration using tools like SSL Labs (ssllabs.com/ssltest), testssl.sh, or nmap with ssl-enum-ciphers script. These tools evaluate cipher strength, protocol versions, certificate chain completeness, HSTS policy, and known vulnerability exposure (POODLE, BEAST, HEARTBLEED, ROBOT). A strong SSL/TLS configuration scores A or A+ on SSL Labs. Key improvements include: enabling only TLS 1.2 and 1.3, using strong ECDHE cipher suites, enabling HSTS with minimum 1-year max-age, adding HSTS preload for browser list inclusion, and configuring OCSP stapling to reduce certificate validation latency for users.