Re: [TLS] WGLC: draft-ietf-tls-tls13-19

[Dr Stephen Henson <[e-mail]>]

On 27/03/2017 08:47, Olivier Levillain wrote:
> 
> For a longer version, post-handshake records of type Handshake can be of
> three kinds:
> - NewSessionTicket (sent by the server, and that can safely be ignored
> entirely by clients)
> - KeyUpdate (sent by either party, requiring only a bit of state)
> - CertificateRequest (sent by the server, an arbirary number of times,
> and requring the client to keep some state *for each request*)
> 
> Of course, this last item makes the post-handshake client state machine
> explode, whereas the first two items can ben implemented in a trivial
> way. The client can not indeed ignore all this state to answer, since it
> is supposed to answer at least with a Finished message, which will cover
> the CertificateRequest message. Moreover, since each of these Finished
> messages must cover the initial handshake and the current
> CertificateRequest message, it requires a forkable hash implementation,
> which requires more memory.
> 

To me allowing the server to send multiple certificate request messages and the
client being permitted to respond to them in arbitrary order adds quite a bit of
complexity.

Is there a usage scenario for this? Would permitting only one outstanding
Certificate Request be too limiting?

On a related note in 4.6.2:

   Note: Because client authentication may require prompting the user,
   servers MUST be prepared for some delay, including receiving an
   arbitrary number of other messages between sending the
   CertificateRequest and receiving a response.

I'm assuming that once the client has responded with a Certificate message it
MUST send CertificateVerify and Finished afterwards and nothing else is
permissible? That is it can't send application data or respond to other
outstanding CertificateRequest messages?

Steve.
-- 
Dr Stephen N. Henson.
Core developer of the   OpenSSL project: http://www.openssl.org/
Freelance consultant see: http://www.drh-consultancy.co.uk/
Email: [e-mail], PGP key: via homepage.