PEM / Certificate Decoder

Decode PEM-encoded X.509 certificates, RSA/EC public keys, and private keys. Shows certificate fields — subject, issuer, validity dates, SANs, and key size — from Base64 DER.

PEM Format Reference

PEM (Privacy-Enhanced Mail) is a Base64-encoded DER (Distinguished Encoding Rules) structure wrapped in -----BEGIN TYPE----- / -----END TYPE----- headers. It is the standard format for TLS certificates, public keys, private keys, and certificate signing requests (CSRs). The underlying structure is ASN.1 - a binary encoding of the certificate's typed fields.

Common PEM types

CERTIFICATE - X.509 TLS certificate (server cert, CA cert, intermediate)
CERTIFICATE REQUEST - CSR to submit to a CA
RSA PRIVATE KEY - PKCS#1 RSA private key
PRIVATE KEY - PKCS#8 unencrypted private key
PUBLIC KEY - SubjectPublicKeyInfo (SPKI) format
EC PRIVATE KEY - Elliptic curve private key

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