What is .crt?

.crt files typically contain X.509 digital certificates that bind a public key to a domain name, organization, or individual. They are used to establish trust for HTTPS, email security, VPNs, and other TLS-based protocols, and may be encoded in PEM (text) or DER (binary) form.

This quick guide explains when to use .crt files, how to open them on any device, and how to share them instantly with FileXhost.

When to use .crt files

You are installing or managing SSL/TLS certificates for websites, APIs, or services.
You need to import a certificate into a server, load balancer, or operating system trust store.
You are working with certificate chains provided by a certificate authority (CA).
You are distributing public certificates to clients or devices so they can validate secure connections.

How to open .crt files

CRT files can be opened with certificate management tools such as OpenSSL, Keychain Access on macOS, the Windows Certificates MMC snap-in, or Linux utilities like openssl and certutil. Double-clicking a CRT on many systems shows a certificate viewer with subject, issuer, validity dates, and usage. When you upload CRT files to FileXhost, they can be shared as downloadable artifacts so operators can import them into servers or trust stores.

Algorithm details

CRT files store X.509 certificates, which contain a subject (identity), issuer, public key, validity period, and extensions describing allowed uses (such as server or client authentication). Internally, certificates are encoded in ASN.1 and serialized as DER (binary) or PEM (Base64-wrapped text). The certificate itself does not include the private key; that is stored in separate KEY or PEM files. Trust is established by chaining the certificate to a trusted root CA via intermediate certificates.

Browser & platform support

Desktop: Browsers consume certificates internally when establishing HTTPS connections but do not open CRT files directly. Users can import trusted certificates into browser or OS stores.
Mobile: Mobile operating systems manage certificates through system settings; CRT files can be imported to trust custom or enterprise CAs.
OS: Windows, macOS, and Linux provide certificate managers and CLI tools to inspect, import, or export CRT files.

Format comparison

Feature	Details
CRT vs CER	CRT and CER are largely interchangeable labels for certificate files; either can be PEM or DER encoded depending on the issuing platform.
CRT vs PEM	PEM describes a text-based container format. A CRT file may use PEM encoding, but PEM files can also contain keys and chains, not just a single certificate.
CRT vs KEY	CRT holds the public certificate, while KEY files hold the private key. Both are required for most TLS server configurations.
CRT vs PFX/P12	PFX/P12 bundles certificates and private keys into a single, usually password-protected, binary container; CRT is typically just the certificate.

How to create crt files

Certificate Authorities: Public or private CAs issue CRT files after validating domain or organization control.
OpenSSL: Generate a certificate signing request (CSR), then receive a CRT from the CA to install on servers.
Enterprise PKI: Internal PKI systems generate and distribute CRT files for corporate devices and services.
Development Tools: Local development environments may generate self-signed CRT files for testing HTTPS.

How to convert crt files

FileXhost: Use FileXhost to store and distribute CRT files so infrastructure teams can download and install them.
OpenSSL CLI: Convert between CRT, CER, PEM, and DER encodings or bundle certificates into PFX/P12 containers.
Certificate Managers: Use platform-specific tools to import/export certificates between different formats and stores.
Online Tools: Some web-based utilities can inspect CRT contents, but avoid uploading sensitive or private material.

Advantages & disadvantages

Advantages

Standard way to distribute public X.509 certificates for TLS and PKI
Recognized by servers, operating systems, and certificate management tools
Can be combined into chains to express trust relationships

Disadvantages

Multiple encodings and extensions (CRT, CER, PEM) can be confusing
Misconfigured certificate chains can cause browser warnings or failed connections
Managing renewals and installations across many servers can be complex without automation

Tools & software

CLI Tools

OpenSSL, certutil, keytool, CFSSL

Servers/Proxies

Nginx, Apache HTTP Server, HAProxy, Envoy, Traefik

OS & Browsers

Windows Certificate Manager, macOS Keychain Access, Linux trust stores, browser certificate managers

Frequently asked questions

Is a CRT file the same as a CER file?

In practice, yes. Both CRT and CER typically contain X.509 certificates and may use PEM or DER encoding. The extension often reflects platform conventions rather than a strict technical difference.

Does a CRT file include the private key?

No. CRT files usually contain only the public certificate. The private key is stored separately, for example in a KEY or PEM file, and must be kept secret.

How do I install a CRT file on my web server?

Follow your server's documentation: usually you reference the CRT (or a combined certificate chain file) along with the corresponding private key in the server configuration, then reload or restart the service.

Can I convert a CRT file to PEM?

Yes. Use OpenSSL or similar tools to convert between DER and PEM encodings, or to rewrap certificates into the desired container format without changing their underlying cryptographic content.

Technical specs

File type: Security
Extension: .crt
MIME type: application/x-x509-ca-cert, application/pkix-cert, application/octet-stream
Compression: Uncompressed
Max file size on FileXhost: Up to 25 MB per file on the free plan and up to 1 GB on Pro FileXhost accounts.

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