SSL Checker Tool

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What Is an SSL Certificate?

An SSL (Secure Sockets Layer) certificate is a digital credential that:

  • 🔒 Encrypts data in transit between a user’s browser and a web server, preventing eavesdropping or tampering.
  • 🆔 Authenticates the server’s identity via a chain of trust rooted in recognized Certificate Authorities (CAs).
  • ✅ Builds trust by showing your site’s padlock icon (or “HTTPS” badge) instead of “Not Secure.”

SSL certificates come in different validation levels:

  • Domain‑Validated (DV): Quick issuance after proving control of the domain.
  • Organization‑Validated (OV): CA verifies your organization’s identity.
  • Extended Validation (EV): The strictest checks, often displaying a green address bar or company name in the browser.

There are also special certificates:

  • Wildcard: Covers one domain and all its subdomains (e.g. *.example.com).
  • Multi‑Domain (SAN/UCC): Secures multiple distinct hostnames in one cert.

Together, SSL certificates form the backbone of web security—encrypting connections, verifying identities, and earning user trust.

SSL Checker Data Fields
Field Description
Subject The certificate’s Common Name (CN), usually the domain.
Issuer The authority that issued the certificate.
From “Valid From” timestamp (YYYY‑MM‑DD HH:MM:SS).
To “Valid To” timestamp (expiry date).
Days Left Number of days until the cert expires.
Serial The certificate’s serial number (hex).
SigAlg The signature algorithm (e.g. SHA256‑RSA).
PubKeyAlg Public key algorithm (RSA/EC/etc.).
PubKeySize Public key size in bits.
SAN Subject Alternative Names (all hostnames/IPs covered).
CRL DP URLs for Certificate Revocation Lists.
AIA OCSP/Authority Info Access URLs.
Fingerprint SHA‑1 SHA‑1 hash of the DER cert.
Fingerprint SHA‑256 SHA‑256 hash of the DER cert.
Why Perform an SSL Check?
  • 🔒 Security – Detect expired or misconfigured certificates.
  • 🌐 Trust – Ensure browsers won’t show “Not Secure.”
  • 🛠️ Maintenance – Plan renewals before expiry.
  • 🚨 Compliance – Verify that you meet industry standards.
How SSL Checking Works

An SSL checker verifies a server’s digital certificate and ensures secure communication. The typical process is:

  1. Initiate secure connection: Open a connection to the server’s HTTPS port (usually 443).
  2. TLS handshake: Client and server exchange protocol versions, cipher suites, and keys to establish an encrypted channel.
  3. Certificate delivery: The server presents its SSL/TLS certificate (and any intermediates) as part of the handshake.
  4. Certificate validation:
    • Check the certificate chain up to a trusted root CA.
    • Verify the certificate has not expired.
    • Confirm the domain name matches a certificate subject or SAN entry.
    • Optionally check for revocation via CRL/OCSP.
  5. Inspect certificate fields: Read key details like issuer, subject, validity dates, public‑key algorithm/size, and extensions (e.g. SANs).
  6. Report results: Surface any errors (expired, mismatched host, untrusted CA, etc.) and show certificate metadata for user review.

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