pki_crypto: Use the new OpenSSL API to write new PKCS#8 PEM files
Since OpenSSL 1.0.0, the "traditional" PEM format was deprecated
in favor of the PKCS#8 PEM files which is more standardized,
more secure and does not depend on the MD5 hash, which is not
available for example in FIPS mode.
This requires using the new EVP_PKEY API for reading private key
Signed-off-by: Jakub Jelen <firstname.lastname@example.org>
Reviewed-by: Andreas Schneider <email@example.com>