Understanding SSL Certificate File Formats

When working with SSL certificates, it is crucial to understand the various file formats. One such format is PEM, which stands for Privacy Enhanced Mail. It is a base64 encoded format that is widely used for SSL certificates. Another format is DER, which stands for Distinguished Encoding Rules. It is a binary format used for digital certificates, public keys, and private keys.

Why Convert PEM to DER?

There are several reasons why you may need to convert a PEM file to a DER file. For example, some applications require DER format instead of PEM. Additionally, some devices may only support DER format. Converting your PEM file to DER ensures compatibility with such applications and devices.

Using OpenSSL Command

OpenSSL is a popular open-source tool used for SSL/TLS encryption and certificate management. It supports various SSL certificate file formats, including PEM and DER. To convert a PEM file to DER using OpenSSL, follow these steps:

Step 1: Install OpenSSL

If OpenSSL is not installed on your system, you need to install it first. You can use the following command to install OpenSSL on Ubuntu:


For other Linux distros, you can use their respective package managers to install OpenSSL.

Step 2: Convert PEM to DER

Once you have installed OpenSSL, you can use the following command to convert your PEM file to DER:

In the above command, replace “cert.pem” with the name of your PEM file and “cert.der” with the name you want to give to your DER file.

Step 3: Verify the Conversion

You can verify the conversion by checking the contents of your DER file using the following command:

This command will display the details of your DER file in human-readable format. If you can see the details, it means the conversion was successful.

FAQs for openssl command to convert pem to der

What is openssl?

OpenSSL is a toolkit implementing SSL/TLS protocols. It is an open-source implementation used for secure communication over the Internet. It provides various cryptographic functions that are widely used to encrypt and decrypt data.

What is a pem file?

.pem is a file format used to store digital certificates and associated private keys. It is commonly used in Unix-based systems for SSL/TLS encryption, CA (Certificate Authority), and website security. PEM files contain encrypted private keys, public keys, and root certificates.

What is a der file?

DER file format is a binary representation of an X.509 certificate or a key. It is usually used to store certificates and keys on Windows systems and in Java-based applications. Instead of textual representations used in PEM format, DER files present everything as binary data.

How to convert pem to der using OpenSSL?

To convert a pem file to der using OpenSSL, use the following command:

openssl x509 -outform der -in certificate.pem -out certificate.der

What does the -outflag indicate in the above command?

The -out flag is used to indicate the output file format for the certificate. Here, we are specifying the output format as der.

What are the other available output file formats?

OpenSSL supports various output file formats such as DER, PEM, PKCS#7, and PKCS#12. You can use appropriate flags to specify the output format accordingly.

Can I use the same command to convert any pem file to der?

Yes, you can use the same command to convert any pem file to der. The only difference will be the name of the input and output files. Make sure to replace the corresponding file names in the command.

Can I convert a der file back to pem using the same command?

Yes, you can use similar commands to convert a der file to pem format. For example, to convert a der file to pem, use the following command:

openssl x509 -inform der -in certificate.der -out certificate.pem

Just like before, make sure to replace the corresponding file names in the command.

Is OpenSSL available for all operating systems?

Yes, OpenSSL is available for most of the operating systems including Linux, macOS, Windows, and other Unix-based systems. You can download and install OpenSSL from their official website or use the pre-installed versions on your system.

Are there any security concerns with OpenSSL?

OpenSSL is widely used and respected in the industry, but as with any software, there is always a potential for vulnerabilities. You should always keep OpenSSL updated to the latest version and follow proper security practices to safeguard your systems.