This unit test case reads an ipsec.secrets file to find an RSA key in it.
It then uses the private key found within to sign something (pseudo-random),
and then uses the public key to validate that the signature was sane.

As an side affect of doing this, the signatures are written to a file
(in binary), which is used in lo04-verifypubkeys.
The public keys can be extracted from the *.secrets file using showhostkey,
using the "make update" target in the lo04-verifypubkeys test case.

