EVP_PKEY_CTX_get_ecdh_kdf_md
if (EVP_PKEY_CTX_get_ecdh_kdf_md(pctx, &kdf_md) <= 0)
int EVP_PKEY_CTX_get_ecdh_kdf_md(EVP_PKEY_CTX *ctx, const EVP_MD **md);