[openssl-users] DTLS over UDP
mcr at sandelman.ca
Mon Feb 19 18:43:08 UTC 2018
Nivedita <maddi.nivedita at gmail.com> wrote:
>> Nivedita <maddi.nivedita at gmail.com> wrote:
>>> I am trying to establish DTLS over UDP connection by using
>>> DTLSv1_listen method .
>>> I have followed the below steps - 1. Created a server socket
>>> and using
>>> this socket created bio and ssl object. bio =
>>> BIO_new_dgram(VI_sock,BIO_NOCLOSE)) SSL_set_bio
>>> 2. Enable cookie exchange on SSL object. SSL_set_options(ssl,
>>> 3. Then started listening using dtlsv1_listen for the new
>>> connections. Once dtlsv1_listen is successful and i got the
>> Nivedita- All the above mentioned steps i am doing on server
>> side . On the
>> client side i have already initiated ssl_connect.
>> On the server side when i am listening using dtlsv1_listen
>> method -
>>> 4. Once i got the peer address , i am creating one more socket
>>> 5. With the new socket i tried to connect to peer address.
> Then once i got the client address from the dtlsv1_listen method,
> i am creating one more socket and trying to connect to this client
I think that I see what is wrong with your flow... you haven't taken the
packet off the original socket, so SSL_accept is still looking for it.
The flow is supposed to be:
1) client sends ClientHello
2) DTLSv1_listen() sees it, and sends a HelloVerifyRequest
(I assume you have filled in the cookie callbacks. I think that
perhaps there should be good cryptographic defaults available in
the library. Maybe there are, and I'm ignorant of them)
3) Client sends ClientHello w/cookie.
DTLSv1_listen() then sees that and tweaks the SSL* to indicate that
the cookie has been accepted. Note that the packet is *LEFT*
on the incoming socket so that SSL_accept() can process it.
This is one the places where the DTLSv1_listen() API is rather
hard to use in my opinion.
4) You make up new sockets, etc.
5) But, you need to call SSL_accept() once with the **old socket** to
process packet that listen() left on it, and then you can switch the
FD over! Of course, you probably want to make sure that SSL_accept()
sends the reply correctly.
What I do in my proposed DTLSv1_accept() API is that I move the data
From the incoming socket to the new BIO's incoming queue:
/* At this point, there is a real ClientHello in serv->init_buf */
memcpy(rb->buf, serv->init_buf->data, serv->init_num);
rb->offset = 0;
rb->left = serv->init_num;
and then remove the packet from the incoming socket. The situation is
then returned like this so that the new sockets can be setup, but the
incoming SSL_accept() BIO is stuffed with the correct (cookie-full)
ClientHello, and replies will go to the right place with the right source
address. I hope to get these patches accepted for the March 11 freeze,
but you might not want to depend upon it.
] Never tell me the odds! | ipv6 mesh networks [
] Michael Richardson, Sandelman Software Works | network architect [
] mcr at sandelman.ca http://www.sandelman.ca/ | ruby on rails [
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