OSSL_PKEY_PARAM_RSA_MASKGENFUNC
const char *key_mgf = OSSL_PKEY_PARAM_RSA_MASKGENFUNC;
param_mgf = OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_RSA_MASKGENFUNC);
OSSL_PARAM_utf8_string(OSSL_PKEY_PARAM_RSA_MASKGENFUNC, NULL, 0), \