X.509 Certificate Decoder
Decode PEM certificates to inspect subject, issuer, SANs, validity dates, and key details.
What is an X.509 certificate?
An X.509 certificate binds a public key to an identity using a digital signature from a Certificate Authority (CA). TLS/SSL certificates used for HTTPS are X.509 certificates. The certificate encodes the subject (owner), issuer (CA), validity period, Subject Alternative Names (SANs), public key, and extensions in ASN.1 DER format, often stored as base64 PEM (Privacy Enhanced Mail) text.
Private & free — this tool runs entirely in your browser.
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