Re: [TLS] DTLS 1.3

[Nikos Mavrogiannopoulos <[e-mail]>]

On Fri, 2016-07-08 at 09:29 +0000, Fossati, Thomas (Nokia - GB) wrote:

> > > > How would the hash chain matching work for a server handling
> > > > multiple
> > > > clients?
> > > Sorry, I'm not sure I understand the question.  Are you asking
> > > what
> > > happens if there is an Id collision between two separate hash
> > > chains?
> > No, my question is much simpler. How would a server handling for
> > example 20000 clients, will figure to which chain a hash of H(x)
> > belongs to? Will it have to iterate through all the chains (client
> > states) and test for matching or there is something more clever
> > than
> > that?
> Ah! The hash chain would be computed at the end of the handshake, so
> all L
> Ids can be put in a hash table that maps them to the same DTLS
> context.
> When a data record comes in, its Id can be used to look up the
> context in
> O(1).
> Clearly the server needs to negotiate a sensible L if it doesn't want
> to blow up.

As long as both the client and the server are able to notify each other
that they only support L=1 I'd be content with it. However, I'd prefer
a simple solution and defer the hash chain negotiation for a separate
extension, since we cannot foresee how and if such an extension will be
used. As we saw with heartbleed any unused complexity is not necessary
adding value.

regards,
Nikos