How to convert a .pfx to .crt & .key file using OpenSSL with a few commands
Looking for a way to convert a .pfx certificate file into a .crt & .key file using OpenSSL? Look no further! This short and easy step-by-step guide will show you how it's done in only 3 commands.
In this tutorial, I will show you how to convert a .pfx file to a .crt & .key file for use on your server or computer's certificate store using OpenSSL. The best part of this is that OpenSSL is absolutely FREE to use! 🥳
Introduction 🚀
Every year our certificates must be renewed and I just encountered this task myself in one of my production environments. I thought writing a quick tutorial on how this is done on a Linux server using OpenSSL would be a good idea.
opensslOpenSSL is a robust and well-documented, full-featured toolbox for working with the Secure Socket Layer (SSL) and Transport Layer Security (TLS) protocols for security. OpenSSL contains a lot of tools for handling cryptography which makes it an ideal choice when we have to work with certificates on both Linux and Windows.
In this case, I already had the .pfx certificate issued by a trusted public certificate authority like DigiCert. There are plenty of certificate authorities out there providing different pricing levels, etc... I'm sure you already got the certificate since you are here.
Below are the commands you have to perform to convert your .pfx certificate to a .crt and .key file without getting a headache. Before we begin, let's have a look at some requirements.
Requirements 🗳️
Below is a list of the things you must bring together in order to follow along in this tutorial.
- OpenSSL has to be installed on your machine. You can read more here: https://www.openssl.org/source/
- The .pfx file and the import password for the certificate.
- A server/computer with either Linux or Windows installed to run the OpenSSL package for converting the certificate.
Get the private .key from the .pfx certificate
The command below will extract the private key from the .pfx file using OpenSSL. All you have to do is enter the command and the import password you created when the certificate was issued originally.
When you are prompted to enter a PEM pass phrase for protecting the .key file, you are free to specify any password you would like. I prefer to use the same as the one I have set for the import password as it makes it easier to remember. But it's totally up to you. 🙌
openssl pkcs12 -in [certificate.pfx] -nocerts -out [keyfile-encrypted.key]What's happening above? 🤔
openssl- This is the command used to invoke the OpenSSL toolkit.pkcs12- It is an OpenSSL command that handles PKCS 12 files, which are a type of archive format used to store cryptographic objects such as certificates, private keys, and related information.-in [certificate.pfx]- This option specifies the input PKCS 12 file, denoted by[certificate.pfx]. The file you provide here should be in the PKCS 12 format and contain one or more certificates, along with the corresponding private key and possibly additional information. This is the .pfx certificate file you got from your certificate authority.-nocerts- This option tells OpenSSL to exclude the certificates from the output. When this flag is used, only the private key and any additional private key-related information will be processed and included in the output file.-out [keyfile-encrypted.key]- This option specifies the output file where the encrypted private key will be stored. The[keyfile-encrypted.key]represents the filename you want to give to the encrypted private key file. OpenSSL will generate or overwrite this file with the encrypted private key.
You should get an output like mine below.
tech-with-christian@swarm-manager:~/certificates$ openssl pkcs12 -in twc-certificate.pfx -nocerts -out twc-private.key
Enter Import Password:
Enter PEM pass phrase:
Verifying — Enter PEM pass phrase:
tech-with-christian@swarm-manager:~/certificates$Get the decrypted .key file from the encrypted private .key file
To get the decrypted .key file for the certificate ( .crt ) we will extract in a moment, we have to run a simple command and provide the PEM password we specified before.
The output will be the decrypted-certificate.key file you can use in combination with the .crt file. Below is the command you have to perform to get the decrypted .key file.
openssl rsa -in [keyfile-encrypted.key] -out [keyfile-decrypted.key]
What happens in the command above? 🤔
openssl- This is the command used to invoke the OpenSSL toolkit.rsa- This OpenSSL command specifically deals with RSA keys.-in [keyfile-encrypted.key]- This option specifies the input file containing the encrypted RSA private key. The[keyfile-encrypted.key]represents the filename of the encrypted private key file you want to decrypt.-out [keyfile-decrypted.key]- This option specifies the output file where the decrypted RSA private key will be saved. The[keyfile-decrypted.key]represents the filename you want to give to the decrypted private key file. OpenSSL will create or overwrite this file with the decrypted private key.
You should get an output like mine below.
tech-with-christian@swarm-manager:~/certificates$ openssl rsa -in twc-private.key -out twc-decrypted.key
Enter pass phrase for twc-private.key:
writing RSA keyYou now have a decrypted .key file that you can use with your .crt file. Let's go and extract the .crt from the .pfx file.
Get the .crt file from the .pfx file
Now that we have extracted the private .key file from our .pfx file, we should get the .crt file. Run the command below and adjust it according to your namings.
openssl pkcs12 -in [certificate.pfx] -clcerts -nokeys -out [certificate.crt]What happens in the command above? 🤔
openssl- This is the command used to invoke the OpenSSL toolkit.pkcs12- This OpenSSL command deals with PKCS 12 files.-in [certificate.pfx]- This option specifies the input PKCS 12 file from which the command will extract certificates.-clcerts- This option instructs OpenSSL to include only the client (user) certificates from the PKCS#12 file. It excludes any CA (Certificate Authority) certificates that might be present. This option is useful when you want to extract only the user certificates for use in client authentication scenarios, for example, when configuring a client to present its certificate to a server.-nokeys- This option tells OpenSSL not to include any private keys in the output. It ensures that only certificates are processed and included in the resulting file.-out [certificate.crt]- This option specifies the output file where the extracted certificate(s) will be saved. The[certificate.crt]represents the filename you want to give to the certificate file. OpenSSL will create or overwrite this file with the extracted certificate(s).
You should get an output like mine below.
tech-with-christian@swarm-manager:~/certificates$ openssl pkcs12 -in twc-certificate.pfx -clcerts -nokeys -out twc-certificate.crt
Enter Import Password:
Bam! 💪 You can now use the .crt file with the .key file on your server/computer to host web applications securely. Install them and power up your solution. 🔥
Summary
In this quick tutorial about converting/extracting a .pfx file to a .crt and .key file you learned a few simple commands. These commands will make it easy for you to perform the extraction process of the certificate files.
If you got any issues, questions, or suggestions for this tutorial, please let me know in the comments below. (available once you sign up for TWC) - Until next time - Happy engineering! ✌️