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CER vs CRT: The Technical Difference & How to Convert Them

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Feeling confused about the differences between CER and CRT files? We can help

CER, CRT, DER, PEM, P7B, P7S, PFX, and P12. Do you feel like pulling your hair when you see so many SSL/TLS certificate formats and extensions? Well, you’re not the only one. In our experience, a person dealing with SSL certificates passes through this stage at least once in their life. So, don’t worry as many have been there (and many are yet to arrive). In the meantime, we want to help by making this phase as short as possible for you.

And that’s why we’ve come up with this article — to help you clear up any confusion regarding CER vs CRT files.

CER vs CRT: What Is the Difference?

Fundamentally, there is no difference between CER and CRT… and yet there is a difference between the two. No, we’re not trying to refer to Schrödinger’s cat here, so relax. What we mean is that both are the same SSL certificate format — that is Base64 (ASCII) format — they both are different filename extensions. This is important because a server might require your certificate filename extension to be in either of the two extensions.

Feeling even more confused? Yeah, we thought so. Essentially, these extensions are used for certificates, and they’re encoded in binary DER or as ASCII PEM formats. CER & CRT extensions are most commonly used by the Unix family of operating systems.

X.509 Certificate Filename Extensions

Technically, all SSL certificates are regarded as types of X.509 certificates. These digital certificates have different filename extensions and formats. Here’s a brief overview of several common filename extensions:

  • .pem — This is a (Privacy-enhanced Electronic Mail) Base64 encoded DER certificate, enclosed between “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–“
  • .cer, .crt, and .der — Although usually in binary DER form, Base64-encoded certificates are also common (see .pem above).
  • .p7b and .p7c — PKCS#7 SignedData structure without data, just certificate(s) or CRL(s).
  • .p12 — PKCS#12 files may contain certificate(s) (public) and private keys (password protected).
  • .pfx — PFX is the predecessor of PKCS#12. This type of file usually contains data in PKCS#12 format (e.g., with PFX files generated in IIS).

Different Servers Require Different Formats & Extensions

As you likely know, there are tons of servers out there. And the (bad) thing about them is that they accept certificate files that are encoded and formatted in a certain manner. So, if you want to install an SSL certificate on your server, you must be aware of the format and extension requirements of your specific server. The good news? Some servers accept multiple certificate file formats.

If they don’t, though, you may find yourself needing to convert a certificate to a different file type. Lucky for you, we know how to do that.

How to Convert Files from CRT to CER

Because CER and CRT files are basically synonymous, they can be used interchangeably by simply changing the extension. So, in case your server requires you to use the .CER file extension, you can convert to .CRT extension easily by implementing the following steps:

  1. Double-click on the yourwebsite.crt file to open it into the certificate display.
  2. Click on the Details tab, and then select the Copy to file button.
  3. Click Next in the certificate wizard.
  4. Choose Base-64 encoded X.509 (.CER), and then click on Next.
  5. Now, browse to store your file and type in the filename that you want to keep
  6. Finally, save the file.

Congratulations! You’ve successfully converted your certificate from CRT to CER.

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