[openssl-users] Interoperating with a legacy client.

Ryan Murray rjkmurray40 at gmail.com
Sat Feb 4 07:38:52 UTC 2017

I made writing to you to ask the team to dispatch some much more then
needed assets for hardware upgrades. I have created a way bill under hacker
one or support at hackerone.com and desperately need this as soon as possible
rather then the back burner. Much more breaking news and head when I get
out of the stone age.
Thanks KS for passing message along
Best regards
Ryan Murray

On Feb 4, 2017 1:36 AM, "Tim Kirby" <tkirby at hotlink.com> wrote:

> I'm writing a server to support a legacy client that uses OpenSSL to
> secure its communication.  The client is using OpenSSL 1.0.1j, and I
> have no control over that.  I'm using the 1.0.1 version of OpenSSL
> supplied with my
> OS for the server side, but that is out of convenience rather than
> necessity.
> My server appears to be working at least semi-correctly, but I have a
> problem with established
> connections being terminated by the server side, and I have run out of
> troubleshooting ideas.
> The client will happily connect to my server, we complete the handshake,
> and start exchanging
> encrypted application data.  Then, it seems like the client wants to
> renegotiate, because it sends the
> server a ClientHello across the established connection.  But something is
> clearly not right, because
> the server responds with a fatal alert and terminates the connection.
> I can watch the connection with wireshark, so I can see in detail what's
> going on, but the client's
> behavior doesn't make sense to me.
> The typical interaction looks like this:
> The client connects to the server.
> The initial ClientHello advertises TLS 1.2 with a record version of 1.0,
> in the cipher suites. Our ServerHello response includes a zero-length
> renegotiation_info extension.  This all seems reasonable.
> The negotiation settles on TLS 1.2, and subsequent application data
> records are sent at that version.  At this point, everything
> seems fine.
> After sending some amount of application data, the client then seems to
> want to renegotiate.  It sends another ClientHello.
> At this point, things have gone wrong.  The second ClientHello looks very,
> very similar to the one sent in the initial handshake.
> The record version is again 1.0, the TLS_EMPTY_RENEGOTIATION_INFO_SCSV is
> included in the cipher suites, and there's no
> renegotiation_info extension present.
> So, if the connection is using TLS 1.2, the server terminates the
> connection with a
> version mismatch alert when it sees the second ClientHello.
> If I force the server to use TLS 1.0, then the server terminates the
> connection because
> of the SCSV present in the ClientHello during renegotiation.
> I'm at a loss.  It seems like the client is misbehaving, if the second
> ClientHello it sends is supposed to be
> a renegotiation attempt.  But misbehaving or not, I still need to
> interoperate with this client.
> Is there something I can do on the server side to be compatible with this
> client?  Is it possible that I'm
> causing the client's behavior through something I'm doing as the server?
> I may be able to provide a sanitized packet trace or packet dissections
> showing the exact behavior I'm seeing, if that would be
> helpful or interesting.
> Any further troubleshooting options would be welcome.
> --
> Tim Kirby
> --
> openssl-users mailing list
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