Certificate Decoder

This X.509 certificate decoder parses SSL/TLS certificates and displays detailed information about the certificate structure, validity, subject, issuer, and extensions.

Features

• PEM Format Support: Decode certificates in PEM format (BEGIN CERTIFICATE)
• Complete Analysis: View all certificate fields and attributes
• Validity Checking: See if certificate is currently valid or expired
• Extension Parsing: Decode certificate extensions (SAN, key usage, etc.)
• Fingerprints: Calculate SHA-1 and SHA-256 fingerprints
• Public Key Details: View public key algorithm and parameters

How to Use

1. Paste your certificate in PEM format (including BEGIN/END lines)
2. Click "Decode Certificate" to analyze
3. Review all certificate details and validity information
4. Use "Load Example" to see a sample certificate

Getting a Certificate

You can get a website's certificate using:

• Browser: Click the padlock icon → Certificate → Copy
• OpenSSL: openssl s_client -connect example.com:443 -showcerts
• Chrome: Developer Tools → Security → View Certificate
• Firefox: Page Info → Security → View Certificate

Understanding X.509 Certificates

• Subject: The entity the certificate identifies (domain, organization)
• Issuer: The Certificate Authority that signed the certificate
• Validity Period: Start and end dates for certificate validity
• Public Key: The cryptographic public key for encryption
• Extensions: Additional features like SAN, key usage, policies
• Signature: Digital signature from the issuing CA