Which MIME types are related to file extension ".cer"?

The .cer file extension is associated with 3 MIME types:

application/pkix-cert, application/x-x509-ca-cert, application/x-x509-user-cert.

A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.

About .cer Files

CER files are digital certificate files used for secure communication and identity verification.
They contain public key infrastructure data following the X.509 standard. The MIME types indicate that they are usually in binary DER encoded certificate format. This means the file holds encrypted information that confirms a server’s or user’s identity.

CER files are often imported into operating systems and web browsers (like Chrome or Firefox) and managed via tools such as Windows Certificate Manager. They are key to establishing trusted connections and enabling encrypted transactions.
Based on information from FilExt.com, these certificates play a critical role in network security and digital authentication.

Relationship between file extension and MIME type

A file extension is a suffix at the end of a filename that indicates what type of file it is. File extensions help both users and operating systems identify what application should be used to open the file.

File extensions are typically separated from the filename by a period (dot) and consist of 2-4 characters, though they can be longer. For example, in the filename "document.pdf", ".pdf" is the file extension.

File extensions are closely related to MIME types, as they both serve to identify the format of a file. However, while MIME types are used primarily by web browsers and servers, file extensions are used by operating systems and applications.

Associated MIME types

application/pkix-cert, application/x-x509-ca-cert, application/x-x509-user-cert

FAQ

What is a MIME type?

A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.

MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.

MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.

How do I find the MIME type for a file?

You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.

Why can one extension have multiple MIME types?

Different programs and historical usage may assign various MIME identifiers to the same file format. Listing them together helps maintain compatibility across tools.