Crear llave (server.key y server.csr) con openssl

Generate your server key

openssl genrsa -des3 -out server.key 1024

Generate your certificate signing request (CSR)

openssl req -new -key server.key -out server.csr

Common Name (eg, YOUR name) []:localhost "localhost o dominio para el cual se quiere crear".

Generate your certificate.

openssl x509 -req -days 1024 -in server.csr -signkey server.key -out server.crt

Referencia:

https://developer.salesforce.com/blogs/developer-relations/2011/05/generating-valid-self-signed-certificates.html