On Thu, Sep 15, 2016 at 11:19 AM, David Woodhouse <dwmw2 at infradead.org> wrote: >> > Until draft-jay-tls-psk-identity-extension happens we *still* have to >> > abuse the session resume protocol to tell the server who we are?, so >> > it's not like it's now a perfect implementation of the DTLS protocol. >> >> I don't think that's the case. The protocol as we have it can work >> perfectly without draft-jay-tls-psk-identity-extension or the session >> id hack we have. The reason we use the hack is to allow the server to >> identify the first packet when it serves many clients, and DTLS >> doesn't have a straightforward way to do that. > > Right. That's what I put in my footnote ? we're only really doing this > to cope with the architecture of the server, which *really* wants to > know from the first packet which client it's dealing with. If it wasn't > for that, we could use the protocol as $DEITY intended. > > If I held a gun to your head? and *made* you change the whole > forawrd_udp_to_owner() thing so that it *did* work with an > unadulterated DTLS protocol and use the PSK identity in a > ClientKeyExchange message... what would it look like? That would work, but would work very inefficiently for a server that likes to handle multiple clients. That is because, instead of the main process forwarding the sessions to the appropriate process/thread it would have to perform a half-handshake just to figure out to which process it should forward the connection. So it would be additional load for a process which is only destined to quickly serve and distribute... So not only it would be technically challenging but would have been sub-optimal as well. That's why I'd like to move on with the dtls1.3 psk username indicator instead (which is brought to tls1.2 by draft-jay-tls-psk-identity-extension). We can implement it in openconnect as well, even now, as gnutls allows an application to register a custom extension, but still we would have to use a custom extension number (protocol is not registered to iana yet). regards, Nikos
