Format Atlas

Guides

Choose a certificate or key file format

Check the destination's required format first, and distinguish an issued certificate, a certificate request, and a private key.

Which format should you choose?

Choose by the role each file plays in your workflow.

  • Text-encoded certificate or key → PEM
  • Issued certificate file → CRT or CER
  • Binary-encoded certificate → DER
  • Container with certificate and private key → PFX or P12
  • Request to a certificate authority → CSR

Do not judge by extension alone

CRT and CER are extensions commonly used for certificates; PEM and DER describe encoding. Check the file's contents, the destination's requirements, and whether a certificate chain is present.

Keep private keys private

PFX/P12 files and some PEM files can contain a private key. Keep them out of public repositories, web directories, chats, and email attachments; apply secure storage and access controls.

Formats to consider

PEM

Good for: Deploying certificates or keys where PEM is required

Less suitable for: Publishing or sharing without inspecting contents

CRT

Good for: Deploying an issued X.509 certificate where requested

Less suitable for: Using it in place of a private key

DER

Good for: Deploying a certificate where DER encoding is required

Less suitable for: Editing as plain text

PFX

Good for: Moving certificates and private keys where PKCS#12 is required

Less suitable for: Storing in a public location

CSR

Good for: Requesting a certificate from a certificate authority

Less suitable for: Deploying as though it were an issued certificate

Before you export

  • Do not publish or share files that may contain private keys.
  • Check expiry, subject names, certificate chain, and destination requirements.

Related comparisons

PEM vs DERPEM and DER can represent the same certificate or key data in different encodings. PEM wraps Base64 text in labeled boundaries; DER is a binary ASN.1 encoding. The extension alone does not identify the contained object.CRT vs PEMCRT is a filename extension commonly used for certificates. PEM is a text encoding that can contain certificates, keys, or related objects; they are not equivalent categories.PEM vs PFXPEM is a text encoding for certificate-related structures; PFX/P12 is a PKCS#12 container that can package certificates and private keys.CSR vs CRTA CSR is a certificate signing request submitted for issuance. CRT is an extension commonly used for an issued certificate; their roles differ before and after issuance.

Guides

Choosing Web Data and Configuration FormatsConsider JSON for machine exchange such as APIs, YAML for configuration people edit, and XML for existing schema-based integrations.Where to keep configuration and secretsSeparate ordinary settings from credentials, then choose a suitable place for local development, CI, and production based on access and exposure risk.

References and specifications