Re: [TLS] FWD: First TLS cached information draft posted

[Simon Josefsson <simon at josefsson.org>]

Sean Shen <sshen at huawei.com> writes:

> Hi, Stefan,
> I support the idea and like the benefit of not transporting Certs.
> The drafts looks good and clear to me, except that I get some questions
> regarding the following part in section 4:
>  
>    Servers that receive an extended client hello containing a
>    "cached_information" extension, MAY indicate that they support one or
>    more of the cached information objects by including an extension of
>    type "cached_information" in the (extended) server hello, which SHALL
>    contain at least one CachedObject received from the client. The
>    CachedObject's returned by the server MUST include the types the
>    server supports and has accepted to replace with a hash of the cached
>    data. 
>  
> It gives me impression that server's reply can include items that is beyond
> cached items which 
> clients provide. Is it possible (or leagal) for clients to use those items
> which he did not 
> mentioned but were indicated usable by server? 
> For example clients provides items {A, B}, server replied {B, C}. 
> B has been confirmed by both sides, C is confirmed only by Server. If B and
> C are both acceptable, 
> but the two negotiation base are not quite same, will there be a problem ?
> Not quite sure it would 
> cause trouble or not though, but wondering whether it will.

Good point.  I don't see how that could work -- how would the server
know whether the client supported C?  The client needs to understand C
in order to parse the handshake properly.

/Simon