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X.509 PEM Certificate & Public Key Inspector

Inspect and parse X.509 PEM certificates locally in-browser. View Subject, Issuer, Validity period, expiry countdown, SANs, and SHA-256 fingerprints.

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📜X.509 PEM Certificate & Public Key Inspector Documentation & Guide

Security & Privacy
The X.509 PEM Certificate and Public Key Inspector decodes and audits SSL/TLS certificates and public keys directly in your browser without transmitting sensitive certificates across external networks.

📋How to Use This Tool

  1. Paste PEM Certificate or Upload: Paste standard PEM text starting with -----BEGIN CERTIFICATE----- or upload any .crt, .pem, or .cer certificate file.
  2. Decode Certificate Metadata: Click Decode and Inspect to parse DER bytes and extract Subject, Issuer, Serial Number, and Validity timestamps.
  3. Review Expiration and SANs: Check the validity badge to see if the certificate is active or expired, how many days remain, and inspect all Subject Alternative Names.
  4. Copy Audit Report or Fingerprints: Copy SHA-256 and SHA-1 fingerprints, or download a structured certificate audit report as a JSON file.

⚙️Technical Specifications and X.509 ASN.1 Parsing

X.509 certificates are standardized public key credentials defined by ITU-T and RFC 5280. Certificates encapsulate identity information, public keys, and cryptographic signatures encoded in Distinguished Encoding Rules (DER) and wrapped in base64 PEM containers.

• Container Formats: Base64-encoded ASCII PEM (RFC 7468) and binary DER byte decoding
• Extracted Fields: Subject DN, Issuer DN, Serial Number, Validity (NotBefore, NotAfter), Public Key Algorithm
• Fingerprint Calculation: SHA-256 and SHA-1 cryptographic hashes calculated over raw DER binary bytes
• SAN Extraction: Subject Alternative Names parser for wildcard domains, subdomains, and IP addresses
• Zero-Knowledge Security: 100% in-browser decoding; private infrastructure certificates are never exposed

In-browser certificate inspection provides a fast, privacy-safe alternative to command-line openssl x509 commands.

💡Practical X.509 Certificate Use Cases

  • Auditing SSL/TLS certificate expiration dates and remaining days before production outages occur.
  • Verifying that wildcards and all required subdomains are included in Subject Alternative Names (SANs).
  • Extracting SHA-256 fingerprints for HTTP Public Key Pinning (HPKP) and mobile app certificate pinning.
100% Client-Side Privacy Guarantee:All calculations, text manipulation, cryptographic hashing, and media conversions execute exclusively within your local browser sandbox. Zero user inputs, financial amounts, credentials, or proprietary files are ever transmitted across networks or logged on external servers.
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