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What is a Pem file and how does it differ from other OpenSSL Generated Key File Formats?

I am responsible for maintaining two Debian servers. Every time I have to do anything with security certificates, I Google for tutorials and beat away until it finally works.

However, in my searches, I often come across different file formats (.key, .csr, .pem) but I've never been able to find a good explanation of what each file format's purpose is.

I was wondering if the good folks here at ServerFault could provide some clarification on this matter?
pki
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2 Answers

akshay1995
PEM on it's own isn't a certificate, it's just a way of encoding data. X.509 certificates are one type of data that is commonly encoded using PEM.

PEM is a X.509 certificate (whose structure is defined using ASN.1), encoded using the ASN.1 DER (distinguished encoding rules), then run through Base64 encoding and stuck between plain-text anchor lines (BEGIN CERTIFICATE and END CERTIFICATE).

You can represent the same data using the PKCS#7 or PKCS#12 representations, and the openssl command line utility can be used to do this.

The obvious benefits of PEM is that it's safe to paste into the body of an email message because it has anchor lines and is 7-bit clean.

RFC1422 has more details about the PEM standard as it related to keys and certificates.
sandhya6gczb
PEM is a container file format often used to store cryptographic keys. It’s used for many different things, as it simply defines the structure and encoding type of the file used to store a bit of data.

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