These are just development certificates, not what is used in production. There is no password on server.key, so you should be able to use these "as is" by updating your ~/.dbhub/config.toml to point at them.
[db4s]
server = "db4s-dev.dbhub.io"
port = 5550
certificate = "/path/to/server.crt"
certificate_key = "/path/to/server.key"
ca_chain = "/path/to/ca-chain.crt"
You'll need to make sure your development DB4S end point server is found in DNS as "db4s-dev.dbhub.io" though, by adding it to your /etc/hosts or similar.
To view the details of a certificate:
$ openssl x509 -noout -text -in somecert.crt