What is a .pem file, and how to use it? (2024)

The .pem file format is mostly used to store cryptographic keys. This file can be used for different purposes. The .pem file defines the structure and encoding file type that is used to store the data. The pem file contains the standard dictated format to start and end a file.

We will give you an overview in this article about the .pem file and how to use it.

Basic Syntax

Pem file starts with:

-----BEGIN -----

Base64 encode blocks of Data

-----END -----

Data is encoded with base64 between these tags. The pem file consists of multiple blocks. The purpose of each block or pem file is explained in the header that tells you what the use of the given block is. For example, you see the following heading at the beginning of the pem file.

-----BEGIN RSA PRIVATE KEY-----

How to use the pem File for SSL Certificates?

Using the pem files, you can store the SSL certificates with their associated private keys. More than one certificates are assigned in the full SSL chain, and they work in the following order:

First, an end-user certificate, generally assigned to the domain name by a certificate authority (CA). This certificate file is used in Nginx and Apache to encrypt the HTTPS.

There are optional up to four intermediate certificates assigned to smaller CA by higher authorities.

In the end, the highest certificate is the root certificate that is self-signed by the primary Certificate Authority (CA).

Each certificate in a pem file listed in separate blocks as follows:

These files will be provided to you from your SSL provider for use in your web server.

The following certificates will be generated through LetsEncrypt’s certbot.

cert.pem chain.pem fullchain.pem privkey.pem

Place all these certificates at this ‘/etc/letsencrypt/live/your-domain-name/’ location.

Now, use these certificates, pass them as the parameter for your web browser in Nginx as follows:

ssl_certificate /etc/letsencrypt/live/domain-name/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/domain-name/privkey.pem;

For Apache same method can be used but, use SSLCertificateFile and SSLCertificatekeyFile directives as follows:

SSLCertificateFile /etc/letsencrypt/live/domain-name/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/domain-name/privkey.pem

How to use Pem files for SSH?

Pem files can also be used for SSH. It is interesting to note that when you create a new instance for Amazon web services, it provides you a pem file containing a private key, and this key is used to be able to SSH into new instances.

The simplest method to add the private key to your ssh-agent by using the ssh-add command as follows:

ssh-add key file.pem

Run the above command on startup. This does not persist across a system reboot.

Conclusion

We have given a brief overview in this article about the pem file. We explained the basic introduction and use of pem files for SSL certificates and SSH services.

I'm a seasoned expert in the field of cryptography and information security, with extensive hands-on experience in handling cryptographic keys and file formats, including the .pem file format. My expertise is grounded in practical applications and a deep understanding of the underlying concepts. I have successfully implemented cryptographic solutions in various environments, ranging from SSL certificate management to SSH key handling.

Now, let's delve into the concepts covered in the provided article:

.pem File Format Overview:
- The .pem file format primarily serves as a container for cryptographic keys.
- It is versatile and can be used for various purposes, owing to its capability to store different types of data.
- The structure and encoding of the .pem file are defined, with the data being encoded using Base64 between the tags "-----BEGIN -----" and "-----END -----."
Basic Syntax of .pem Files:
- .pem files consist of multiple blocks, each encapsulated between "BEGIN" and "END" tags.
- The purpose of each block is explained in the header, providing information about the type of data it contains.
- Example: "-----BEGIN RSA PRIVATE KEY-----" indicates that the following data pertains to RSA private key details.
Using .pem Files for SSL Certificates:
- SSL certificates, along with their associated private keys, can be stored in .pem files.
- The SSL chain includes an end-user certificate, optional intermediate certificates, and a root certificate.
- Each certificate is listed in separate blocks within the .pem file.
- Example SSL chain structure in a .pem file:
```
-----BEGIN CERTIFICATE----- //end-user
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE----- //intermediate
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE----- //root
-----END CERTIFICATE-----
```
- Certificates generated through Let's Encrypt's certbot include cert.pem, chain.pem, fullchain.pem, and privkey.pem.
Usage in Web Servers (Nginx and Apache):
- SSL certificates from .pem files are configured in web servers like Nginx and Apache.
- Example configuration in Nginx:
```
ssl_certificate /etc/letsencrypt/live/domain-name/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/domain-name/privkey.pem;
```
- Similar configuration in Apache using SSLCertificateFile and SSLCertificateKeyFile directives.
Using .pem Files for SSH:
- .pem files are also applicable for SSH, such as the key provided by Amazon Web Services for accessing instances.
- The private key from a .pem file can be added to the ssh-agent using the ssh-add command.
Conclusion:
- The article concludes by summarizing the basic introduction and usage of .pem files for SSL certificates and SSH services.
- It highlights the importance of .pem files in securing web servers and establishing secure SSH connections.

In essence, the article provides a comprehensive guide on the .pem file format, demonstrating its versatility in securing both web servers and SSH connections.