Refactor low-level crypto to C++ style. #3823

Job	Run time
cmake-offline-googletest	4m 26s
cmake-offline-googletest-src	4m 7s
system-sexpp, sexpp shared libs on, rnp shared libs on	3m 25s
system-sexpp, sexpp shared libs on, rnp shared libs off	3m 20s
system-sexpp, sexpp shared libs off, rnp shared libs on	3m 26s
system-sexpp, sexpp shared libs off, rnp shared libs off	3m 8s
package-source	34s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 19s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 21s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 9s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 1s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	4m 8s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 18s
package	1m 14s
debian-tests	1m 0s
	49m 56s

Provide feedback