What is the difference .CER vs .CRT :
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Fundamentally, there is no difference between cer and crt and yet there is a difference between the two.
What i 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.
These extensions are used for certificates, and they're encoded in binary der or as ascii pem formats.
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.CER & .CRT extensions are most commonly used by the unix family of operating systems.
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.CER vs .CRT Comparison
Comparison: .CER vs .CRT
Overview
.CER and .CRT are file extensions for digital certificates. They are often interchangeable but differ in naming conventions and primary environments.
.CER
- Definition: Stands for "Certificate". Commonly used in Windows environments.
- Format: Supports both DER (binary) and PEM (Base64-encoded) formats.
- Use Cases: Used to store public key certificates issued by Certificate Authorities (CA).
- File Association: Can be opened directly in Windows Certificate Viewer.
.CRT
- Definition: Short for "Certificate". Primarily used in Unix/Linux environments.
- Format: Also supports both DER and PEM formats.
- Use Cases: Commonly used in web server configurations (e.g., Apache, Nginx).
- File Association: Typically referenced in Unix/Linux applications.
Key Similarities
Both file extensions serve similar purposes, as shown below:
| Feature |
.CER |
.CRT |
| Purpose |
Represents a digital certificate. |
Represents a digital certificate. |
| Format |
Supports both DER and PEM formats. |
Supports both DER and PEM formats. |
| Contains Private Key? |
No, only public certificates and metadata. |
No, only public certificates and metadata. |
Key Differences
| Feature |
.CER |
.CRT |
| Primary Environment |
Windows environments. |
Unix/Linux environments. |
| Default Association |
Opens with Windows Certificate Manager. |
Used in web server configurations (e.g., Apache, Nginx). |
Practical Notes
- Interchangeable Use: The difference is mostly in naming conventions. You can rename `.cer` to `.crt` or vice versa without affecting functionality.
- Conversion: Ensure the file content (DER or PEM format) matches the application's requirements.
Example Commands
Check certificate details using OpenSSL:
openssl x509 -in certificate.crt -text -noout
Convert `.crt` (DER) to `.cer` (PEM):
openssl x509 -inform DER -in certificate.crt -out certificate.cer -outform PEM
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