OpenSSL 3 non-deprecated APIs are not implemented

[pemensik]

I started looking inside ldns and have found it masks deprecated API calls for OpenSSL 3 by CFLAGS="-DOPENSSL_API_COMPAT=10100 $CFLAGS" in configure. Quite a lot of functionality still requires deprecated calls. At least creating DSA and RSA keys should be converted into EVP_PKEY_fromdata usage and create directly EVP_PKEY from functions like ldns_key_buf2rsa_raw.

While it should be possible to keep backward compatibility when those APIs are still available, I think possibility to use only non-deprecated APIs should be started on. Eventually it would have to be required to switch. At least optional support would be great for a start.

EVP_PKEY-RSA(7), OSSL_PARAM_int(3ossl) and OSSL_PARAM_BLD manuals might help.

That would be prerequisite for implementing EVP_PKEY_CTX_new_from_name key creation using alternative providers as a replacement for ENGINE support deprecated.

[pemensik]

Once that done, I think ldns_key_buf2rsa and ldns_key_buf2dsa functions should be marked deprecated and have alternative functions, which would provide directly EVP_KEY. Avoiding use of the RSA structure in functions like ldns_verify_rrsig_rsasha256_raw. Together with all other functions accessing non-EVP structures. ldns_key_set_rsa_key, ldns_key_set_dsa_key, ldns_key_new_frm_fp_rsa, ldns_key_new_frm_fp_dsa would be other examples.