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Certificate Decoder

Decode SSL certificates from PEM, DER, or base64 format. View certificate details, validity, and issuer information.

🛠️ How to Use
  1. Paste the certificate in PEM format or upload a .crt/.pem/.cer/.der file.
  2. Click Decode Certificate.
  3. Review Subject, Issuer, Validity, Key details and Fingerprints.
  4. Use Download or Copy to save the original certificate.
Example (PEM)
-----BEGIN CERTIFICATE-----
MIIFazCCA1OgAwIBAgIR...
-----END CERTIFICATE-----
Note: For .der/.cer files, we auto-convert to PEM for decoding.

What is an SSL Certificate Decoder?

An SSL certificate decoder is a tool that reads and displays the information contained within an SSL/TLS certificate. Certificates are encoded in formats like PEM (Base64) or DER (binary), making them difficult to read directly. Our decoder extracts and presents this information in a human-readable format.

SSL certificates contain crucial information about website identity, encryption capabilities, and validity periods. Understanding this information helps you verify certificate authenticity, troubleshoot SSL issues, and ensure proper security configuration.

Why Decode SSL Certificates?

✓ 1. Verify Certificate Details Before Installation

Before installing a certificate on your server, decode it to verify:

  • → Correct Domain: Ensure the certificate is issued for your domain
  • → Validity Period: Check the certificate hasn't expired and has reasonable validity
  • → Issuer Information: Confirm it's from a trusted Certificate Authority
  • → Key Strength: Verify adequate encryption strength (2048-bit or higher)

🔧 2. Troubleshoot SSL Errors

When encountering SSL errors, decoding certificates helps identify:

  • Name mismatches between certificate and domain
  • Expired or not-yet-valid certificates
  • Missing Subject Alternative Names (SANs)
  • Weak encryption algorithms
  • Incorrect certificate chain order

🛡️ 3. Security Audits and Compliance

Security professionals decode certificates to:

  • Verify compliance with security policies
  • Check for weak cryptographic algorithms
  • Audit certificate inventory across infrastructure
  • Validate certificate transparency logs
  • Ensure proper key usage extensions

📊 4. Certificate Management

Organizations managing multiple certificates use decoders to:

  • Track expiration dates across all certificates
  • Identify certificates needing renewal
  • Verify certificate deployment matches requests
  • Document certificate details for compliance

Understanding Certificate Information

📋 Subject Information

The subject identifies who the certificate is issued to:

  • • CN: Primary domain
  • • O: Organization name
  • • OU: Department
  • • L: City/Locality
  • • ST: State/Province
  • • C: Country code

🏢 Issuer Information

The Certificate Authority that signed and issued the certificate. Trusted CAs include DigiCert, Let's Encrypt, Sectigo, and GlobalSign.

📅 Validity Period

Certificates have defined validity periods:

  • • Valid From date
  • • Valid To (expiration)
  • • Max 398 days validity

🔑 Public Key Info

Encryption details:

  • • Algorithm (RSA/ECDSA)
  • • Key Size (2048/4096-bit)
  • • Min: 2048-bit RSA

🔐 Fingerprints

Unique identifiers:

  • • SHA256 (recommended)
  • • SHA1 (being phased out)
  • • MD5 (legacy only)

Certificate Formats Explained

📄 PEM Format (Privacy Enhanced Mail)

The most common format for certificates:

  • Base64 encoded text
  • Begins with -----BEGIN CERTIFICATE-----
  • Human-readable when decoded
  • Can contain multiple certificates

💾 DER Format (Distinguished Encoding Rules)

Binary format for certificates:

  • Binary encoded, not human-readable
  • Smaller file size than PEM
  • Common in Windows environments
  • File extensions: .der, .cer

🔒 PKCS#12 Format (PFX)

Password-protected archive:

  • Contains certificate and private key
  • File extension: .pfx, .p12
  • Requires password to extract
  • Common for backup and transfer

💡 Best Practices

  • ✓ Always decode certificates before installation to verify correctness
  • ✓ Check domain names match exactly including www prefix
  • ✓ Verify minimum 2048-bit key size for security
  • ✓ Confirm issuer is a trusted Certificate Authority
  • ✓ Never share private keys - only certificates are safe to decode publicly
  • ✓ Regularly audit certificates for weak algorithms or expiring dates

Frequently Asked Questions

❓ Can I decode a certificate from a live website?

Yes, but you'll need to export it first. Use your browser's certificate viewer to export the certificate, then decode it with our tool. Alternatively, use our SSL Certificate Checker to analyze live certificates directly.

❓ What's the difference between decoding a certificate and a CSR?

Certificates are signed by a CA and contain validity periods, issuer information, and signatures. CSRs (Certificate Signing Requests) are unsigned requests sent to CAs to obtain certificates. Use our CSR Decoder for CSRs.

❓ Is it safe to decode certificates online?

Yes, certificates are public information and safe to decode. However, never upload private keys to any online tool. Our decoder only processes certificates, not private keys.

🔗 Related Tools

Enhance your certificate management with these complementary tools:

SSL Certificate Checker CSR Decoder Private Key Matcher Certificate Fingerprint