SSL/TLS Certificate & Key Decoder

Differences in PEM File Types

Common Base64-encoded text format (PEM) files frequently used in practice.

• •CRT / CER The 'public key certificate' signed by a Certificate Authority (CA). Configured on the server and presented to clients.
• •CSR A 'signing request' file used to request a certificate from a CA. It contains the public key and applicant information (Distinguished Name).
• •KEY The 'private key' that must be securely stored on the server. Generated when creating a CSR and works as a pair with the CRT. It must never be leaked.

Distinguished Name (DN) Abbreviations

Abbreviations for attributes used in the certificate's SUBJECT and ISSUER fields.

• •CN Common Name. The FQDN target for SSL communication (e.g., www.example.com). *Note: Modern validation primarily relies on SANs instead.
• •O Organization. Company or organization name
• •OU Organizational Unit. Department or division name
• •L Locality. City or town
• •ST State/Province
• •C Country. 2-letter country code

About SANs (Subject Alternative Names)

An extension field that allows a single certificate to secure multiple domains or subdomains. Modern browsers (like Google Chrome) have strictly enforced security standards, ignoring the CN value and exclusively verifying the domain names (or wildcards like *.example.com) listed in SANs. Because of this, configuring SANs is mandatory for modern SSL certificates.