anchor.diff:  , openssl
   , cryptography_vectors
   , darwin
  -, idna
   , asn1crypto
   , packaging
   , six
  
positive.code:   buildInputs = [ openssl cryptography_vectors ]
               ++ stdenv.lib.optional stdenv.isDarwin darwin.apple_sdk.frameworks.Security;
    propagatedBuildInputs = [
      idna
      asn1crypto
      packaging
      six
  
negative.code: buildPythonPackage rec {
    # also bump cryptography_vectors
    pname = "cryptography";
    version = "2.5";
  
    src = fetchPypi {
      inherit pname version;
      sha256 = "00c4d7gvsymlaw0r13zrm32dcnarmpayjyrh65yymlmr6mrbcij9";
    };
  
    outputs = [ "out" "dev" ];
  