[openssl-dev] Contributing to TLS 1.3 - Where to start?

[Thiago Arrais]

Thank you, Matt.

I actually am _not_ familiar with the spec. I was looking for some work on
OpenSSL exactly because I want to know TLS better.

Your suggestion seems like a good start. It is pretty dense, but that was
exactly what I was looking for.

Thank you again.

-- Arrais

On Tue, Apr 4, 2017 at 2:10 PM Matt Caswell <matt at openssl.org> wrote:

>
>
> On 04/04/17 15:34, Thiago Arrais wrote:
> > Hmmm... The Getting Started page talks about writing test cases.
> >
> > It seems like a good start. Is there any area that needs special
> attention?
>
> Actually I have a suggestion for a fairly small self-contained piece of
> work suitable for a starting project.
>
> The spec has this requirement:
>
>    As of TLS 1.3, servers are permitted to send the "supported_groups"
>    extension to the client.  If the server has a group it prefers to the
>    ones in the "key_share" extension but is still willing to accept the
>    ClientHello, it SHOULD send "supported_groups" to update the client's
>    view of its preferences; this extension SHOULD contain all groups the
>    server supports, regardless of whether they are currently supported
>    by the client.  Clients MUST NOT act upon any information found in
>    "supported_groups" prior to successful completion of the handshake,
>    but MAY use the information learned from a successfully completed
>    handshake to change what groups they use in their "key_share"
>    extension in subsequent connections.
>
> At the moment we only ever send supported_groups client -> server. Never
> server -> client. I wouldn't worry about the client acting on this
> information at this stage. Just start with the server sending it if the
> selected key_share is not for the most preferred group.
>
> Hint: you will need to look at ssl/statem/extensions.c and you will also
> need to add code to ssl/statem/extensions_srvr.c.
>
> I strongly suggest you spend some time looking at some other github pull
> requests to get a feel for how our submission and review process works,
> and the kind of review comments that come up. You should also
> familiarise yourself with our coding style:
>
> https://www.openssl.org/policies/codingstyle.html
>
> All submissions should include tests. Adding something to
> test/recipes/70-test_tls13messages.t would probably be sufficient, i.e.
> a test to demonstrate that sending a preferred key_share results in no
> supported_groups extension in the EncryptedExtensions message, and then
> a test to demonstrate that sending an acceptable but non-preferred
> key_share results in the supported_groups extension being sent.
>
> If you are not already familiar with the TLSv1.3 spec then you will need
> to be. Make sure you read it through and gain a good understanding of it
> before you start.
>
> Matt
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