Understanding the Basics of OpenSSL
OpenSSL is a powerful tool that enables users to manage digital certificates on Linux. One of the essential functions of OpenSSL is to convert certificate files from one format to another. In this article, we will focus on how to convert a PEM file to a Cer file using OpenSSL.
What is a PEM File?
PEM stands for Privacy Enhanced Mail, and it is a base64-encoded format that stores SSL certificates and keys. PEM files are widely used in Linux environments and can be easily transferred from one system to another. PEM files can contain multiple certificates and keys, making them a versatile way of storing SSL/TLS data.
What is a Cer File?
Cer files are also certificate files used in Windows environments. However, unlike PEM files, Cer files are binary-encoded and can only contain one certificate. Cer files are commonly used in Microsoft Exchange and Active Directory environments.
Converting PEM to Cer Using OpenSSL
To convert a PEM file to a Cer file, we will use the OpenSSL command-line tool. Here are the steps involved:
- Open a terminal window and navigate to the directory where the PEM file is located.
- Run the following command to convert the PEM file to a Cer file:
“`
In the above command, replace “cert.pem” with the name of your PEM file and “cert.cer” with the name you want to give the Cer file.
- Press enter, and OpenSSL will convert the PEM file to a Cer file.
OpenSSL is a versatile tool for managing digital certificates in Linux environments, and can be used to convert certificate files from one format to another. PEM files are base64-encoded and can store multiple certificates and keys, while Cer files are binary-encoded and can only contain one certificate, making it useful for Windows environments like Microsoft Exchange and Active Directory. The OpenSSL command to convert PEM to Cer involves using the x509 command with options to specify the input and output file formats and names. There are many other commands in OpenSSL that can be used to manage digital certificates, such as generating RSA private keys, creating certificate signing requests, managing X.509 digital certificates, and testing SSL/TLS connections.
Understanding the Command
The OpenSSL command we used to convert the PEM file to a Cer file has several parts. Here’s what each part means:
openssl: This is the command to launch the OpenSSL tool.x509: This is the command to manage digital certificates.-inform PEM: This option specifies that the input file format is PEM.-in cert.pem: This option specifies the name of the input file.-outform DER: This option specifies that the output file format is DER, which is the binary format used in Cer files.-out cert.cer: This option specifies the name of the output file.
Other OpenSSL Commands
OpenSSL offers many other commands that can be used to manage digital certificates. Here are some of the most commonly used OpenSSL commands:
openssl genrsa: This command is used to generate RSA private keys.openssl req: This command is used to generate certificate signing requests (CSR).openssl x509: This command is used to manage X.509 digital certificates.openssl pkcs12: This command is used to create and manage PKCS#12 files, which are used to store certificates and private keys.openssl s_client: This command is used to test SSL/TLS connections to remote servers.
FAQs for OpenSSL Convert PEM to CER
What is the difference between PEM and CER format?
PEM and CER are two different formats for certificate files. PEM (Privacy-Enhanced Mail) is a Base64 encoded ASCII file with a header and footer that consists of “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–“. CER (Microsoft Serialized Certificate) is a binary format used by Microsoft Windows.
How to check if a certificate is in PEM format?
You can open the certificate file with any text editor and look for “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–” tags. If these tags exist, then the certificate is in PEM format.
How to convert PEM to CER using OpenSSL?
OpenSSL is a free and open-source software library that provides various cryptographic functions. To convert a PEM file to a CER file, use the following command:
openssl x509 -inform PEM -outform DER -in certificate.pem -out certificate.cer
In this command, replace “certificate.pem” with the name of your PEM file and “certificate.cer” with the name you want for your CER file. The “-inform PEM” option indicates that the input file is in PEM format, while the “-outform DER” option indicates that the output should be in binary format.
Can CER files be converted back to PEM?
Yes, it is possible to convert a CER file back to PEM format using OpenSSL. The command for this conversion is:
openssl x509 -in certificate.cer -inform DER -out certificate.pem -outform PEM
In this command, replace “certificate.cer” with the name of your CER file and “certificate.pem” with the name you want for your PEM file. The “-inform DER” option indicates that the input file is in binary format, while the “-outform PEM” option indicates that the output should be in PEM format.
Why would someone need to convert a certificate from PEM to CER?
Certificates in different formats are required for different purposes. CER files are commonly used by Microsoft Windows for various applications such as web browsers, email clients, and VPN connections. If a certificate in PEM format needs to be used in a Windows environment, it must be converted to CER format first.
Is OpenSSL available for all operating systems?
OpenSSL is a cross-platform software library that can be used on various operating systems such as Linux, Windows, macOS, and Unix-like systems. You can download OpenSSL binaries or source code from the official website or use the pre-installed OpenSSL on some operating systems.