Use AES (the successor of DES) to encrypt private key. Further
reading:

* http://csrc.nist.gov/publications/nistpubs/800-131A/sp800-131A.pdf
* https://ssllabs.com/downloads/SSL_TLS_Deployment_Best_Practices.pdf
"3DES provides about 112 bits of security. This is below the
recommended minimum of 128 bits, but it's still strong enough. A
bigger practical problem is that 3DES is much slower than the
alternatives. Thus, we don't recommend it for performance reasons,
but it can be kept at the end of the cipher list for
interoperability with very old clients."

* http://csrc.nist.gov/publications/nistpubs/800-67-Rev1/SP-800-67-Rev1.pdf

Use SHA256 for our CA. This avoids accidental use of SHA1 or MD5 which
could be default values.

Signed-off-by: Lorenz Leutgeb <lorenz.leutgeb@gmail.com>