To export a CRT file certificate using OpenSSL in the Windows DOS prompt, you must first ensure OpenSSL is installed and accessible via your system PATH. Locate the target certificate file (typically a
.cer or
.crt) and use the
openssl x509 command with the
-in flag to specify the source, the
-out flag to define the destination filename, and the
-outform PEM argument to explicitly set the output encoding. This process converts the binary DER format often found on Windows systems into the standard Base64-encoded PEM format required by most web servers and applications.
Prerequisites and Environment Setup
Before attempting any cryptographic operations, verify that the OpenSSL utility is correctly installed on your Windows machine. While many Linux distributions include OpenSSL by default, Windows users often need to install it manually or through package managers like Chocolatey or Scoop. Once installed, open the Command Prompt (DOS) and type
openssl version. If the command returns a version number, the tool is available in your environment variables. If you receive an error stating that 'openssl' is not recognized, you must add the OpenSSL installation directory to your system's PATH environment variable or navigate directly to the
bin folder where the executable resides.
It is crucial to distinguish between the certificate file itself and the private key. The
<code>.crt</code> or
<code>.cer</code> file contains the public key and identity information of the server or user. It does not contain sensitive private data. Therefore, exporting this file is generally safe and non-destructive, unlike exporting private keys which may require specific permissions or password protections depending on how they were generated.
Identifying the Source Certificate Format
Windows Certificate Manager typically exports certificates in DER (Distinguished Encoding Rules) format, which appears as binary garbage when opened in a text editor. OpenSSL defaults to expecting PEM (Privacy-Enhanced Mail) format, which is ASCII-based and starts with
-----BEGIN CERTIFICATE-----. If your source file is in DER format, you must inform OpenSSL of this during the conversion process. You can identify the format by opening the file in Notepad; if it looks like unreadable binary characters, it is DER. If it shows readable text starting with BEGIN/END markers, it is already PEM.
For DER files, you will need to use the
-inform DER flag. For PEM files, this flag is optional but can be included for clarity. Understanding this distinction prevents the common error where OpenSSL fails to parse the input file because it assumes the wrong encoding.
Executing the Export Command
The core operation involves running a single command line instruction. Navigate to the directory containing your certificate file using the
cd command. Then, execute the following structure:
openssl x509 -in input.cer -out output.crt -outform PEM
If your input file is in DER format, modify the command to include the input format specification:
openssl x509 -inform DER -in input.cer -out output.crt -outform PEM
Here is a breakdown of the parameters:
- -in: Specifies the path to the source certificate file.
- -out: Specifies the path and name for the newly created exported file.
- -outform PEM: Ensures the output is written in Base64 encoded ASCII format, which is compatible with Apache, Nginx, and most modern TLS configurations.
- -inform DER: (Optional) Tells OpenSSL that the input file is in binary DER format rather than PEM.
After execution, verify the success of the operation by opening the new
output.crt file in a text editor. It should now display readable text beginning with
-----BEGIN CERTIFICATE----- and ending with
-----END CERTIFICATE-----.
Handling Common Errors
Users frequently encounter issues related to file permissions or incorrect paths. Ensure that the current user has read access to the source file and write access to the destination directory. A common mistake is forgetting to include the file extension in the
-in parameter, leading OpenSSL to look for a file that does not exist. Another frequent issue arises when the certificate is part of a chain. The basic
x509 command only processes a single certificate. If you need to export a full chain, you may need to concatenate multiple certificates or use different tools, though for simple single-certificate extraction, the method above is sufficient.
For more complex scenarios involving Certificate Authorities, such as setting up local trust stores or automating renewals, refer to our guide on
Windows Certificate Authority. Additionally, if you are dealing with configuration errors specifically within the OpenSSL setup on Windows, check our troubleshooting article on
Troubleshooting Invalid openssl.cfg File in Windows.
Verification and Best Practices
Once the certificate is exported, it is good practice to verify its contents using the terminal. You can run
openssl x509 -in output.crt -text -noout to display detailed information about the certificate, including the issuer, validity period, and subject. This confirms that the export was successful and the file is valid. Always store exported certificates in secure locations if they are part of a larger infrastructure, even though they only contain public information. Never attempt to export private keys using this specific method, as
x509 operates solely on public certificates. For procedures involving private keys, consult resources on
Exporting non-exportable private key for .cer from Windows Certificate Manager, noting that those processes are significantly more restricted due to security policies.
Frequently Asked Questions
Can I convert a CRT file to DER format instead?
Yes, you can change the output format by replacing
-outform PEM with
-outform DER in your command. This creates a binary file suitable for certain legacy Java applications or embedded systems that expect raw DER encoding rather than Base64 text.
What if my certificate file has a .pem extension?
If your file already has a
.pem extension and contains ASCII text, you likely do not need to change the format at all. However, if you want to ensure consistency or rename it to
.crt, you can still run the same command without the
-inform flag, as OpenSSL will auto-detect PEM format.
Why does OpenSSL say "unable to load certificate"?
This error usually means the input file is corrupted, the path is incorrect, or the format is misidentified. Check that the file exists in the specified directory and verify whether it is DER or PEM. If it is DER, ensure you have included the
-inform DER flag in your command line.
Does this process extract the private key as well?
No, the
openssl x509 command only handles public certificates. Private keys are stored separately and are not included in
.crt or
.cer files. Extracting a private key requires different commands and access to the original key storage location.
Is it safe to share the exported CRT file?
Yes, it is safe. The CRT file contains only public information, such as your domain name, organization details, and public key. It does not contain any secret data that could compromise your server's security if shared publicly.