Making own personal certificate, exporting private key in .key format
i want to make my own certificate (not a SSL one for domain, just personal), which has to be a file with .crt extension. I have the .csr file by clicking "Request certificate" for my key in PGP Desktop: created a plain txt document , copy-pasted the text with "Begin certificate request---...--- End" and renamed to certificate.csr.
I tried to use OpenSSL to do that, with using command
openssl x509 -req -days 365 -in certificate.csr -signkey myprivate.key -out certificate.crt
however, i got error with the private key loading. i cannot find how to export my private key. i can only export my public key, resp. private keyring but not in format .key but .skr. how can i export my private key in format .key? or how to make .crt certificate from .csr ?