Re: [TLS] Remove deprecated fields in TLS 1.3

[David Benjamin <[e-mail]>]

On Mon, Apr 3, 2017 at 12:29 AM Benjamin Kaduk <[e-mail]> wrote:

> On 04/02/2017 03:33 AM, Arnaud Venturi wrote:
>
> I could not think of any security or interoperability issue with this
> proposal, the only drawback I can see being the slight complexity added
> in ClientHello parsing.
>
>
> The ClientHello message needs to be interpreted in the same way by TLS
> servers running all versions of TLS.  A TLS 1.0 server would not know to
> use the changed interpretation of the fields and would fail to negotiate a
> connection.  Basically, no change in the format is possible while
> preserving the backwards and forwards compatibility of version negotiation.
>

I believe the idea is that, if you support TLS 1.2 and below, you send a
1.2-compatible ClientHello. If you don't, then you send the proposed
ClientHello. Servers would be required to support both formats.

This change would save us all of 3 bytes in the ClientHello, so my feeling
is this isn't worth the trouble of having two formats and all the trouble
that entails. (Servers having to parse both formats, code in servers that
won't be exercised for years, clients worrying about whether servers
implemented that, etc.)

David