[zeromq-dev] TLS (openssl) for ZeroMQ

[Luca Boccassi]

On Tue, 2018-12-25 at 00:53 +0100, 林宝龙 wrote:
> The problem of first option we met is that OpenSSL provides a lot
> configurable things, for example, trust group, external verification
> callback, etc. We must add more options to sockopt to have such
> things
> configurable. For the callback functions, if we continue using
> setsockopt,
> we need to cast function pointer to void pointer and vice versa,
> looks not
> good.

As mentioned, there is really no alternative to continue supporting
bindings. Also, exposing a third party API/ABI again would mean that
the users would need to start worrying about OpenSSL's API/ABI changes,
and keep them in sync with the internal usage of the library. That
would not be maintainable.

So it looks like there are both legal and implementation problems. So
let's take a step back: why is the current encryption/authentication
support via CURVE and GSSAPI not sufficient? What is lacking that you
need in your application?

> About the licence issue, I'm not familiar with those licenses, and I
> have
> asked someone inside my company, got the answer that I can use
> OpenSSL in
> libzmq with an exception, I don't know how. He said that we will
> share the
> code out in the end, but can't contribute back to libzmq directly.
> Does it
> same as what you concern? Do you have more information that we must
> stop
> using OpenSSL inside libzmq?

Yes an exception is needed as I said, but not just from you: from every
single copyright holder of libzmq, of which there are many. That's
because adding an exception to the license is a change in license, and
cannot legally be done unilaterally.

Note that this is not only a problem for contributing code back, but
also for your application. You cannot distribute those changes to
anybody without a license change, which means you cannot give your
application to anybody without breaching the terms of the license, and
thus copyright law.

> On Mon, 24 Dec 2018, 23:42 Luca Boccassi <luca.boccassi at gmail.com
> wrote:
> 
> > On Mon, 24 Dec 2018, 23:03 林宝龙 <lbl52001 at gmail.com wrote:
> > 
> > > Hi,
> > > 
> > > We are adding TLS support for ZeroMQ(based on 4.2.5). Product
> > > reason, we
> > > choosed OpenSSL as TLS library.
> > > 
> > > Ask community for suggestions, which solution below is better?
> > > 1. Use TLS public certification, private key, etc as socket
> > > option (set
> > > through setsockopt), ZeroMQ manages the OpenSSL context,
> > > one  OpenSSL
> > > context per socket_base_t object.
> > > 2. Use OpenSSL context as socket option(set through setsockopt),
> > > external
> > > application should provide the OpenSSL context, with public
> > > certification,
> > > private key, etc. set in context level, all ssl connections share
> > > the same
> > > configuration as the input OpenSSL context.
> > > 
> > > At beginning we choosed the first solution, like curve, use
> > > public
> > > certification, private key as the socket option. But later on, we
> > > found the
> > > second solution that use external OpenSSL context can make the
> > > ZeroMQ code
> > > simpler, and more flexible, external application can configure
> > > the OpenSSL
> > > context without change the ZeroMQ socket options.
> > > 
> > > Welcome your comments.
> > > 
> > > Best regards,
> > > Baolong
> > > 
> > 
> > The first option would be better, exposing third party API and ABI
> > would
> > be a nightmare, especially for bindings. O
> > 
> > But the most important issue is that the Openssl license is not
> > compatible
> > with libzmq, which is licensed under the lgpl3, so I'm afraid such
> > combination will not be legally distributable. At least not without
> > a
> > relicensing effort to add an exception - we are already trying that
> > to
> > change to mpl2 and are nowhere near done unfortunately.
> > 
> > > _______________________________________________
> > 
> > zeromq-dev mailing list
> > zeromq-dev at lists.zeromq.org
> > https://lists.zeromq.org/mailman/listinfo/zeromq-dev
> > 
> 
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-- 
Kind regards,
Luca Boccassi
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