What is PEM Format?

Problem

What is PEM Format?

Solution

PEM or Privacy Enhanced Mail is a Base64 encoded DER certificate. PEM certificates are frequently used for web servers as they can easily be translated into readable data using a simple text editor. Generally when a PEM encoded file is opened in a text editor, it contains very distinct headers and footers. Below are some examples of different files in PEM format.

-----BEGIN CERTIFICATE REQUEST-----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-----END CERTIFICATE REQUEST-----

Above is the example of a CSR (certificate signing request) in PEM format. You can see that PEM has the characteristics of containing a header, the body (which consists mainly of code) and footer.

The header and footer is what identifies the type of file, however be aware that not all PEM files necessarily need them.

-----BEGIN CERTIFICATE REQUEST----- and -----END CERTIFICATE REQUEST----- show a CSR in PEM format.
-----BEGIN RSA PRIVATE KEY----- and -----END RSA PRIVATE KEY----- show a private key in PEM format.
-----BEGIN CERTIFICATE----- and -----END CERTIFICATE----- show a certificate file in PEM format.