OpenSSL Convert PEM Cert to DER: A Comprehensive Guide

Understanding PEM and DER Certificate Formats

Before delving into the specifics of converting PEM to DER, it’s important to understand what these formats are and how they differ. PEM (Privacy Enhanced Mail) is a base64 encoded format commonly used for securing emails and web servers. PEM certificates are ASCII text files that usually have extensions such as .pem, .crt, or .cer. On the other hand, DER (Distinguished Encoding Rules) is a binary format used for digital certificates.

Advantages of PEM Certificates

PEM certificates offer several advantages over DER certificates. Firstly, they are more widely used and supported by various platforms and applications. Secondly, they are easier to read and modify as compared to DER certificates. Lastly, they can be easily converted to other formats such as PKCS#7 and PKCS#12.

Advantages of DER Certificates

DER certificates are more secure than PEM certificates due to being binary rather than text-based. They are harder to modify and tamper with, making them ideal for situations where security is of utmost importance. Additionally, they are more compact than PEM certificates and use less storage space.

Converting PEM Certificates to DER Format

Converting a PEM certificate to DER format involves using the OpenSSL command-line tool. The following steps outline the process:

Open a command prompt or terminal window.
Navigate to the directory where the PEM certificate is located.
Enter the following command: openssl x509 -in cert.pem -outform der -out cert.der
Substitute “cert.pem” with the name of the PEM certificate you wish to convert.
The converted DER certificate will be saved in the same directory with the name “cert.der”.

PEM and DER are two different certificate formats. PEM certificates are ASCII text files that are base64 encoded and widely used in various platforms and applications. They can be easily read and modified and transformed to other formats like PKCS#7 and PKCS#12. DER certificates, on the other hand, are binary and harder to modify or tamper with, making them ideal in secure situations. They are more compact and use less storage space than PEM certificates. Converting a PEM certificate to DER can be done using the OpenSSL command-line tool and can be verified for validity using the same tool. Other commonly used certificate formats include PKCS#7, PKCS#12, JKS, CRT, and P7B.

Breaking Down the Command

Let’s break down the above command to understand what each part does:

openssl: This is the command-line tool we are using.
x509: This option specifies that we are working with an X.509 certificate.
-in: This option specifies the input file (the PEM certificate).
cert.pem: This is the name of the input file.
-outform: This option specifies the output format (DER).
der: This is the output format we want.
-out: This option specifies the output file name.
cert.der: This is the name we want to give to the output file.

Verifying the Conversion

Once the conversion is complete, it’s a good idea to verify that the resulting DER certificate is valid and can be used. This can be done using the OpenSSL command-line tool as well. The following steps outline the process:

Navigate to the directory where the DER certificate is located.
Enter the following command: openssl x509 -in cert.der -inform der -text -noout
Substitute “cert.der” with the name of the DER certificate you wish to verify.
If the certificate is valid, you should see information about it displayed in the terminal window.

PEM certificates are ASCII text files commonly used for securing emails and web servers, while DER certificates are binary formats used for digital certificates. PEM certificates are more widely used and supported while DER certificates are more secure and use less storage space. To convert PEM to DER, use the OpenSSL command-line tool. Verifying the resulting DER certificate can also be done using the same tool. Other common certificate formats include PKCS#7, PKCS#12, JKS, and CRT.

Other Certificate Formats

In addition to PEM and DER formats, there are several other certificate formats that are commonly used. Some of these formats are:

PKCS#7: This format is used to store and transmit multiple certificates and private keys. It is also known as P7B or .p7b format.
PKCS#12: This format is used to store private keys with their associated certificates. It is also known as PFX or .pfx format.
JKS: This format is used by Java applications to store private keys and certificates. It is also known as Java KeyStore format.
CRT: This is a Microsoft Windows certificate format used for storing certificates.
P7B: This is a Microsoft Windows certificate format used for storing multiple certificates.

FAQs for openssl convert pem cert to der

What is openssl?

OpenSSL is an open source software library for implementing the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols, as well as a full-strength general-purpose cryptography library.

What are PEM and DER formats for certificates?

PEM (Privacy Enhanced Mail) and DER (Distinguished Encoding Rules) are two different formats used for X.509 digital certificates. PEM format uses base64 encoding and can contain multiple certificates and private keys, while DER format is a binary format and can only contain a single certificate or a certificate chain.

How do I convert a PEM certificate to DER format using OpenSSL?

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

openssl x509 -in <input_file.pem> -outform der -out <output_file.der>

This command takes the input file in PEM format (specified by the -in option), and converts it to DER format (specified by the -outform option). The output is saved in the specified output file in DER format (specified by the -out option).

Can I convert multiple PEM certificates to a single DER file?

No, you cannot convert multiple PEM certificates to a single DER file. DER format can only contain a single certificate or a certificate chain, while PEM format can contain multiple certificates and private keys. Therefore, if you have multiple PEM certificates, you will need to convert each certificate to DER format separately.

How do I verify that the conversion was successful?

To verify that the conversion was successful, you can use the OpenSSL command-line tool to view the contents of the DER certificate file. You can use the following command to display the certificate information:

openssl x509 -inform DER -in <output_file.der> -noout -text

This command displays the certificate information in human-readable format. If the command displays the certificate information without any errors, then the conversion was successful.

Is it possible to convert a DER certificate to PEM format using OpenSSL?

Yes, it is possible to convert a DER certificate to PEM format using OpenSSL. You can use the following command to convert a DER certificate to PEM format:

openssl x509 -inform DER -in <input_file.der> -out <output_file.pem>

This command reads the input file in DER format (specified by the -inform option), and converts it to PEM format. The output is saved in the specified output file in PEM format (specified by the -out option).