SN_sha256
digestname = SN_sha256;
if (!EVP_MD_is_a(hash_alg, SN_sha256)) {
int digest_unapproved = !EVP_MD_is_a(md, SN_sha256)
&& !EVP_MD_is_a(md, SN_sha256)
int digest_unapproved = !EVP_MD_is_a(md, SN_sha256)