.key · application/x-pem-file
What is a .key file?
Private Key File
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Our Certificate Decoder reads it in your browser — no upload, no install.
Open the Certificate Decoder →About the format
A .key file conventionally holds a PRIVATE key — the secret half of a certificate's key pair, usually in PEM text form (BEGIN PRIVATE KEY, BEGIN RSA PRIVATE KEY, or BEGIN ENCRYPTED PRIVATE KEY when password-protected). This is the most sensitive file in the whole certificate ecosystem: whoever holds the server's key can impersonate the server and, in older non-forward-secret configurations, decrypt captured traffic. Handling rules are short and absolute: it never leaves the server it belongs to except through deliberate, protected channels; permissions restrict it to the service that needs it; it never goes into email, chat, tickets or version control (secret scanners hunt for BEGIN PRIVATE KEY in repos for good reason); and if exposure is even suspected, the certificate is reissued and the old one revoked. Everyday tasks with a .key: pairing it with a certificate in web-server config, confirming key-and-cert match (compare public-key fingerprints), and adding or removing its password with openssl.
How to open a .key file
Windows
- WhyCrashed Certificate Decoder (browser — checks type/size and cert match locally)
- openssl pkey
macOS
- openssl pkey
Linux
- openssl pkey
Is a .key file dangerous?
It's a SECRET, not malware. Leaking it compromises everything its certificate protects. Never share it.
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