Accepts .pem, .pfx and .p12. PFX and P12 files ask for their password; PEM files never do.
Everything runs locally in your browser. No file or password is uploaded.
How it works
- Load a .pem, .pfx or .p12 file. PFX and P12 ask for the password.
- Pick the new Not Before and Not After. They start at now and now plus one year.
- Download the certificate. Subject, issuer, serial number, public key, private key and every extension are kept byte for byte; only the two dates change.
The dates are part of what a certificate's signature covers, so changing them always invalidates the original signature. With the private key at hand (RSA), the certificate is signed again with it: a self-signed certificate stays fully valid, which is what you want for test and development certificates. A certificate issued by a real CA cannot be extended this way — it has to be renewed by that CA.