JDK-8219568 extended master secret performance problems
Xuelei Fan
xuelei.fan at oracle.com
Tue Apr 9 21:43:16 UTC 2019
On 4/9/2019 1:04 PM, Daniel Jeliński wrote:
> Hi Xuelei,
> What's the verdict on allowing legacy resumption on server even when EMS
> is enabled?
>
If EMS is used, no legacy resumption any more. Otherwise, the problem of
the legacy resumption comes.
> I was thinking of repurposing the current allowLegacyResumption flag for
> this; its name looks appropriate. However, it would be a change of
> behavior: currently we do not allow legacy resumption, and default value
> of allowLegacyResumption is true; we would either need to change the
> default, or change the default behavior. Would that be acceptable?
Currently, if no EMS, the behavior in server side may look like:
1. close the connection if allowLegacyResumption is false;
2. perform full handshake if allowLegacyResumption true;
Default allowLegacyResumption is true for compatibility reasons.
Does it sound reasonable to you?
Xuelei
> Regards,
> Daniel
>
> pon., 8 kwi 2019 o 21:00 Xuelei Fan <xuelei.fan at oracle.com
> <mailto:xuelei.fan at oracle.com>> napisał(a):
>
> Hi Daniel,
>
> Thanks for the quick feedback. It helps me a lot.
>
> On 4/8/2019 9:59 AM, Daniel Jeliński wrote:
> > Hi Xuelei,
> > Thanks for your response!
> > My understanding is that legacy resumption = resumption of a session
> > that was established without extended master secret extension.
> >
> > Our Java application is a web server that is communicating with a
> large
> > number of clients, majority of which are built on top of OpenSSL
> 1.0.2,
> > which does not implement extended master secret. The clients send
> data
> > to server using frequent short-lived connections.
> >
> > When we use Java pre-8u161 or disable extended master secret
> > (/jdk/./tls/.useExtendedMasterSecret=false), the usual workflow
> is as
> > follows:
> > - client connects to server for the first time
> > - Full handshake happens, server creates a session ID and caches it
> > - session is established, data is transferred, connection is closed.
> > Later:
> > - subsequent client connection sends the cached session ID
> > - server resumes session using abbreviated handshake
> > - data is transferred, connection is closed.
> >
> > The same workflow with extended master secret enabled is as follows:
> > - client connects to server for the first time
> > - Full handshake happens, server creates a session ID and caches it
> > - session is established, data is transferred, connection is closed.
> > Later:
> > - subsequent client connection sends the cached session ID
> > - server checks that the session ID was established without extended
> > master secret and rejects it. Full handshake happens, server
> creates a
> > session ID and caches it
> > - session is established, data is transferred, connection is closed.
> >
> It sounds like a reasonable use case if applications want to take the
> risks. I will think more about if we can make an enhancement to allow
> legacy resumption again if the extended master secret extension is
> not used.
>
> > Full handshake is much more expensive than abbreviated handshake,
> and
> > caching thousands of session IDs that are never reused creates a
> burden
> > on GC.
> >
> > My understanding of RFC 7627 is that rejecting abbreviated handshake
> > when extended master secret is not used makes sense only when we are
> > using client certificates for authentication. We are not using
> client
> > certificates in our communication, so we would prefer to resume
> sessions
> > whether extended master secret is used or not.
> >
> > TLS specification does not require the server to assign a session ID
> > when it knows it will not allow the client to resume session. We
> should
> > take advantage of that and not assign a session ID when the user
> does
> > not want to resume legacy sessions.
> >
> Good idea!
>
> Thanks,
> Xuelei
>
> > Let me know if that makes sense now.
> > Thanks,
> > Daniel
> >
> >
> > pon., 8 kwi 2019 o 17:43 Xuelei Fan <xuelei.fan at oracle.com
> <mailto:xuelei.fan at oracle.com>
> > <mailto:xuelei.fan at oracle.com <mailto:xuelei.fan at oracle.com>>>
> napisał(a):
> >
> > Hi Daniel,
> >
> > Was extended master secret extension used when legacy
> resumption is
> > expected? I did not get the point from JDK-8219568 and this
> > description. It would be helpful if there is a test code to
> reproduce
> > the behavior.
> >
> > Thanks,
> > Xuelei
> >
> > On 4/6/2019 11:36 AM, Daniel Jeliński wrote:
> > > Hi all,
> > > Ever since upgrading to Java 8u161 we are running into
> performance
> > > problems that were caused by the implementation of extended
> > master secret.
> > >
> > > First problem was described in 8219568; server does not allow
> > resuming
> > > legacy sessions even when jdk.tls.allowLegacyResumption is
> set to
> > true.
> > > Based on the mail archives of the original discussion [1]
> and the
> > > release notes [2] I think this was not what was intended.
> Should the
> > > setting (jdk.tls.allowLegacyResumption) on the server side
> work like
> > > this instead?
> > > allow = true -> proceed with abbreviated handshake
> > > allow = false -> proceed with full handshake
> > >
> > > Documentation is ambiguous enough that we would probably
> not even
> > need
> > > to change it. Today it states that setting
> allowLegacyResumption to
> > > false rejects abbreviated handshakes, without clarifying
> what the
> > > default does.
> > >
> > > Second problem is that while the server rejects the
> abbreviated
> > > handshake, it generates and caches a new session ID on
> every client
> > > reconnect, effectively thrashing the session cache. These
> IDs are
> > never
> > > used. Should we stop generating session IDs when legacy
> > resumption is
> > > disabled?
> > >
> > > Regards,
> > > Daniel
> > >
> > >
> > > [1]
> > >
> >
> http://openjdk.5641.n7.nabble.com/Code-Review-Request-JDK-8148421-Extended-Master-Secret-TLS-extension-td311192.html
> > > [2] https://bugs.openjdk.java.net/browse/JDK-8192045
> >
>
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