Re: [TLS] TLS Next Proto negotiation

Adam Langley <agl@google.com> Mon, 18 July 2011 12:43 UTC

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Date: Mon, 18 Jul 2011 08:43:30 -0400
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From: Adam Langley <agl@google.com>
To: gswaru@rediffmail.com
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Cc: tls <tls@ietf.org>
Subject: Re: [TLS] TLS Next Proto negotiation
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On Mon, Jul 18, 2011 at 8:22 AM, <gswaru@rediffmail.com>; wrote:
> I have gone the TLS NPN draft, it talks about the new handshake message Next Protocol handshake message which is sent from Client to server after Change cipher spec and before Finish. But when I capture the packet with NPN enable(using google chrome to browse google web services), I find NULL NPN extnesion is sent from client to server and server is responding back with NPN extension with the protocol. But there is no next protocol handshake message sent by client after change cipher spec, instead I see a strange encrypted packet from Server side even before server is sending change cipher spec, this is on new session.

Make sure that you're looking at the draft which reflects the current
implementation:
http://tools.ietf.org/html/draft-agl-tls-nextprotoneg-02

The strange, encrypted message from the server is probably a session
ticket. Wireshark, at least in some versions, doesn't understand it
and incorrectly describes it as encrypted.

If the NPN extension exchange happened then the NextProtocol message
will be sent. Again, Wireshark doesn't dissect it very well and may
believe that it was merged into the Finished message; you'll have to
look at the bytes yourself. In the particular Chrome implementation,
the NextProtocol message is sent in its own record, so you can see the
framing without having to decrypt anything.


Cheers

AGL