linux - openssl PEM certificates , base64
PEM Format
The PEM format is the most common format that Certificate Authorities issue certificates in. PEM certificates usually have extensions such as .pem, .crt, .cer, and .key.
They are Base64 encoded ASCII files and contain "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----" statements.
Server certificates, intermediate certificates, and private keys can all be put into the PEM format.