I wanted to understand the replay attack vulnerability in case of enable early data of TLS 1.3 while false start is secure in that respect as I have read from https://github.com/openssl/openssl/issues/1541
So, with false start, the application data is sent from client after the first leg of the handshake i.e. one round trip is complete, so the data goes encrypted even though the handshake is not completed. In enable early data mode in TLS 1.3 for 0-RTT for session resumption, the application data is sent from the client along with the client hello message. Does the application data in early data mode go as clear text ? I assume this is also encrypted using the PSK because 0-RTT is only applicable when PSK is available on the client side. How is it vulnerable to replay attack. Please help me understand.
Is there any API available in OpenSSL for false start ?
Thanks
Best regards,
Neetish
On Tue, Jun 20, 2017 at 11:52 AM, Neetish Pathak <npathak2@xxxxxxxx> wrote:
I Appreciate your responseOn Tue, Jun 20, 2017 at 2:09 AM, Matt Caswell <matt@xxxxxxxxxxx> wrote:
On 19/06/17 19:11, Neetish Pathak wrote:
> 2) Can you suggest some places to put a time stamp in OpenSSL code.
I agree with Ben's responses to all your other questions. For this
question, I'm not sure what you are trying to achieve? Starting before
SSL_accept/SSL_connect and finishing after they return should be fine.
Or are you looking for a breakdown of where the time is going?
Thanks Matt. I was asking for a breakdown since I was not sure if the SSL_accept and SSL_connect just do the handshake or if they are doing some other things that may impact latency and CPU usage. Just wanted to be clear that calling SSL_connect starts ClientHello , SSL_accept unblocks on receiving ClientHello and sends ServerHello, and both functions return after sending Finished message from their sides (i.e. client and server).Matt
>
> Thanks
> Best Regards,
> Neetish
>
> On Mon, Jun 19, 2017 at 5:49 AM, Matt Caswell <matt@xxxxxxxxxxx
> <mailto:matt@xxxxxxxxxxx>> wrote:
>
>
>
> On 16/06/17 23:51, Neetish Pathak wrote:
> > Thanks Matt, Appreciate ur response and tips
> >
> > On Fri, Jun 16, 2017 at 3:36 PM, Matt Caswell <matt@xxxxxxxxxxx <mailto:matt@xxxxxxxxxxx>
> <https://mta.openssl.org/mail> > <mailto:matt@xxxxxxxxxxx <mailto:matt@xxxxxxxxxxx>>> wrote:
> >
> >
> >
> > On 16/06/17 20:08, Benjamin Kaduk via openssl-users wrote:
> > > On 06/16/2017 01:58 PM, Neetish Pathak wrote:
> > >> Hello
> > >> Thanks
> > >> I tried reading some content from the server side and I
> observed the
> > >> new_session_cb getting invoked in that case on the client
> side. I
> > >> understand that may be due to delayed NewSession info
> transfer from
> > >> server side to client side. But it is helpful for saving
> the session
> > >> info on the client side. (Thanks Matt for your input)
> > >>
> > >> However, now I have two concerns
> > >>
> > >> 1) I see that latency for handshake with session resumption in
> > TLS 1.3
> > >> has not improved as much as it improves for TLS 1.2
> > >> With TLS 1.3, I observed that resumption brings down the
> connection
> > >> time from 2.5 ms to 1.2-1.3 ms
> > >> while with TLS 1.2 (using either session IDs or tickets), the
> > >> connection time reduces from 2.5 ms to 0.5-0.6 ms.
> > >>
> > >> The whole code is similar for running the two experiments
> with only
> > >> max TLS version changed. Can someone comment on the latency
> > >> measurements for the two cases.
> > >> TLS 1.3 is supposed to be better than TLS 1.2 in my
> opinion. Please
> > >> comment.
> > >>
> > >
> > > Are you seeing a HelloRetryRequest in the resumption flow?
> That would
> > > add an additional round trip. (Your numbers in milliseconds
> are of
> > > course not transferrable to other systems; round-trips is an
> easier to
> > > understand number.) RFC 5246 and draft-ietf-tls-tls13-20
> both have
> > > message-flow diagrams that show the number of round trips in
> various
> > > handshake flows.
> >
> > Care should also be taken about when you are starting your
> "timer" and
> > when you stop it, e.g. if you stop your timer after the
> session ticket
> > data has been received by the client then this is not a "fair"
> test (the
> > connection is ready for data transfer earlier than the arrival
> of the
> > session ticket).
> >
> > I would expect to see the TLS1.3 latency for a full handshake
> to be
> > around the same as for a TLS1.2 resumption handshake. With a
> TLS1.3
> > resumption only marginally different. There are the same
> number of round
> > trips for a TLS1.3 full handshake as that there are for a
> resumption
> > one. The primary difference is that the Certificate message is
> not sent
> > (which can be quite a large message).
> >
> > Your timings suggest you are testing this over a LAN where the
> effects
> > of network latency are going to be relatively low. The real
> benefits
> > from fewer round trips will really be seen when network
> latency is more
> > significant.
> >
> >
> >
> > In my application program, I put start and stop timer before and after
> > SSL_accept on server side and before and after SSL_connect on the
> client
> > side.
>
> That should be fine (my worry was that you might also be including the
> subsequent session ticket transfer).
>
> > I am not sure how I can put timers at individual steps of Handshake
> > using my client applications. I was assuming SSL and SSL_accept take
> > care of the entire handshake process.
> >
> > Yes, I am testing on local machine. I will migrate my test to remote
> > machines. But I am not really able to understand why TLS 1.3 is slower
> > on my machine.
>
> If you are on a local machine I would not expect a significant speed up
> in TLSv1.3 vs TLSv1.2. TLSv1.3 has been designed to reduce the number of
> round-trips required in order to avoid unnecessary network latency. If
> you are on a local machine then there isn't any significant network
> latency anyway - so timings are presumably dominated by the CPU
> intensive tasks. You should make sure that you are comparing like with
> like, i.e. the same ciphers, key lengths, key exchange algorithms,
> curves etc between TLSv1.2 and TLSv1.3. Differences in any one of these
> could obviously have significant performance impacts.
>
> Matt
>
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