SSL certificates are integral to secure communication between web servers and clients. These certificates, which come in various types and formats, are used to encrypt sensitive information such as credit card numbers, login credentials, and personal information. In this article, we will explore the process of converting PEM certificates to CER format using OpenSSL, a widely-used open-source software providing a robust, full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols.

Understanding the PEM Certificate Format

PEM (Privacy Enhanced Mail) is an ASCII encoding format used to store secure cryptographic keys, certificates, and other related data. PEM files typically have extensions such as .pem, .crt, .cer, and .key. These files contain base64-encoded data, which is then encapsulated between “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–” delimiters.

PEM files can contain multiple certificates, which are separated by blank lines. These files are widely used in various applications such as Apache, Nginx, and OpenSSL-based software.

Advantages of PEM Certificates

PEM certificates have several advantages, including their widespread use, compatibility with various applications, and ease of understanding. In addition, PEM certificates can be easily converted to other formats using tools such as OpenSSL.

Understanding the CER Certificate Format

CER (or .cer) is a binary format used to store X.509 certificates, which are typically used for SSL/TLS encryption. CER files are commonly used in Microsoft Windows operating systems and are used to store digital certificates in the form of binary data.

CER files can contain a single certificate and are typically used in applications such as Internet Explorer, Microsoft Outlook, and Microsoft Exchange Server.

Advantages of CER Certificates

CER certificates have several advantages, including their compatibility with Microsoft products, their ability to store binary data, and their ease of use.

Converting PEM to CER using OpenSSL

To convert a PEM certificate to CER format using OpenSSL, you can use the following command:

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This command uses the x509 utility to convert the certificate in PEM format (-inform PEM) to DER format (-outform DER) and then saves the output to a file with the .cer extension (-out certificate.cer).

Understanding the OpenSSL Options

The openssl command provides several options for converting certificates, including:

• -inform: Specifies the input format for the certificate. In this case, we are using PEM format.
• -in: Specifies the input file name.
• -outform: Specifies the output format for the certificate. In this case, we are using DER format.
• -out: Specifies the output file name. In this case, we are using the .cer extension.

Disadvantages of PEM Certificates

Although PEM certificates have several advantages, they also have some disadvantages. For example, PEM certificates are not easily portable due to the use of ASCII encoding, and they are not very secure due to the lack of encryption.

Disadvantages of CER Certificates

Although CER certificates have several advantages, they also have some disadvantages. For example, CER certificates are not as widely used as PEM certificates and are not as easily convertible to other formats.

Other OpenSSL Commands

In addition to the x509 utility, OpenSSL provides several other commands for managing certificates, including:

• req: Used to generate certificate signing requests.
• genpkey: Used to generate private keys.
• pkcs12: Used to convert certificates between different formats, including PKCS#12.
• s_client: Used to test SSL connections.
• s_server: Used to create SSL servers.

FAQs about converting certificate pem to cer openssl

What is a PEM certificate and what is a cer certificate?

PEM and cer are different formats for digital certificates. PEM stands for Privacy Enhanced Mail, and is a base64-encoded DER certificate, enclosed between “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–“. Cer, on the other hand, is a binary format for X.509 public key certificates, typically used in Windows environments.

How can I convert a PEM certificate to a cer certificate with OpenSSL?

You can convert a PEM certificate to a cer certificate using the OpenSSL command-line tool, by running the following command: openssl x509 -inform PEM -in certificate.pem -outform DER -out certificate.cer. This command will read the certificate in PEM format from the input file “certificate.pem”, convert it to the binary cer format, and write it to the output file “certificate.cer”.

Why would I want to convert a PEM certificate to a cer certificate?

There are several reasons why you might want to convert a PEM certificate to a cer certificate. For example, if you are working with a Windows system that requires cer certificates, or if you are installing a certificate in IIS or another Windows-based web server. Additionally, some applications may only accept certificates in cer format, so converting a PEM certificate to cer can ensure that the certificate is compatible with those applications.

What are some other OpenSSL commands that can be used for working with certificates?

OpenSSL provides a wide range of commands for working with digital certificates. For example, you can use the openssl x509 command to display information about a certificate, the openssl req command to generate a certificate signing request, and the openssl ca command to sign a certificate request and issue a new certificate. The openssl pkcs12 command can be used to create PKCS#12 files that contain a private key and certificate in a single file. You can explore the full range of OpenSSL commands by consulting the documentation or running the “openssl help” command.