Privacy Enhanced Mail, which is a type of Public Key Infrastructure (PKI) file used for storing certificates and keys. PEM is the most common format type that Certificate Authorities (CAs) use for issuing certificates. PEM certificates usually have the following extensions: .pem, .crt, .cer, and .key. As compared to a more secure PKCS #12 type, PEM files are text-based and simply list the certificates and keys in the format of Base64 encoded ASCII strings.