Use openssl utility to determine cipher used to encrypt the private key.
Create and encrypt RSA or EC private key using general utilities. There are multiple possibilities, so let me sum it up.
Create and encrypt RSA or EC private key using dedicated utilities.
Different ways to provide encryption password when using OpenSSL utility.
Use OpenSSL utility to encrypt or decrypt files.
Define IP address inside multi-domain SSL certificate.
Check if the certificate matches DNS name or IP address
Create a multi-domain SSL certificate without a common name.