Test Your Knowledge
SSL/TLS Certificate Decoder
Parse and analyze X.509 certificates. Paste a PEM-encoded certificate to view subject, issuer, validity period, and extensions. All processing happens in your browser.
Load Sample:
Certificate Status
Subject
Issuer
Validity
Public Key
Extensions
Fingerprints
Certificate Fields Explained
| Field | Description |
|---|---|
| Subject | The entity the certificate is issued to (domain, organization) |
| Issuer | The Certificate Authority that issued the certificate |
| Serial Number | Unique identifier assigned by the CA |
| Not Before | Certificate start date (valid from) |
| Not After | Certificate expiration date |
| Subject Alternative Names (SAN) | Additional domains/IPs covered by the certificate |
| Key Usage | Allowed operations (signing, encryption, etc.) |
| Basic Constraints | Whether it's a CA certificate and path length |
Certificate Best Practices
- Use 2048-bit RSA or 256-bit ECC keys minimum
- SHA-256 or better for signature algorithm
- Short validity periods - 90 days (Let's Encrypt) to 1 year max
- Include all required SANs - www and non-www versions
- Monitor expiration - Set up alerts 30 days before expiry
- Use Certificate Transparency logs for monitoring
- Implement OCSP Stapling for revocation checking
- Avoid wildcards when possible - limit scope
Related Resources
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