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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">I suppose one could abuse SSL_set_msg_callback() to create a filter that rewrites the initial re-handshake message into something innocuous. Though I doubt that would work,
once the client starts a handshake, it expects a response from the server, and may well time out and close if it does not get one. The way TLS works, it is always the client starting a renegotiation. The server can send a message asking the client to renegotiate,
but the client can ignore that. I don’t believe the opposite is true.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> openssl-users [mailto:openssl-users-bounces@openssl.org]
<b>On Behalf Of </b>Sashank Mullapudi (samullap)<br>
<b>Sent:</b> Monday, November 28, 2016 10:56 PM<br>
<b>To:</b> openssl-users@openssl.org<br>
<b>Cc:</b> Ram Mohan R (rmohanr) <rmohanr@cisco.com>; Nikhil Mittal (nimittal) <nimittal@cisco.com>; Anil Kumar (anilkum) <anilkum@cisco.com><br>
<b>Subject:</b> Re: [openssl-users] Disabling Client-Initiated TLS renegotiation<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Resending this hoping for a response from someone who has information on disabling TLS renegotiation from the Client side.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Thanks,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Sashank<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black">From:
</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black">samullap <<a href="mailto:samullap@cisco.com">samullap@cisco.com</a>><br>
<b>Date: </b>Tuesday, 22 November 2016 at 12:21 PM<br>
<b>To: </b>"<a href="mailto:openssl-users@openssl.org">openssl-users@openssl.org</a>" <<a href="mailto:openssl-users@openssl.org">openssl-users@openssl.org</a>><br>
<b>Cc: </b>"Ram Mohan R (rmohanr)" <<a href="mailto:rmohanr@cisco.com">rmohanr@cisco.com</a>>, "Anil Kumar (anilkum)" <<a href="mailto:anilkum@cisco.com">anilkum@cisco.com</a>>, "Nikhil Mittal (nimittal)" <<a href="mailto:nimittal@cisco.com">nimittal@cisco.com</a>><br>
<b>Subject: </b>Disabling Client-Initiated TLS renegotiation<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">Hi,</span><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">As part of securing our web interfaces, we wanted to disable client-initiated TLS renegotiation. </span><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:black">The reasoning for this requirement </span><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333;background:white">is as follows- </span><i><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333">Generally,
renegotiation of TLS sessions is much more resource-intensive for the server than the client, and should therefore not be performed at will to avoid degrading performance. Disabling client from renegotiating secures the server from undergoing a DoS attack
due to continuous renegotiation requests.</span></i><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333">I<span style="background:white"> see that there is an option </span></span><b><span style="font-size:10.0pt;font-family:"Calibri",sans-serif;color:black">SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION</span></b><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333;background:white">,
but that is to secure the renegotiation, not disable it.</span><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333">I<span style="background:#FFFEFE"> wanted to check if there is a patch or flag available to disable any negotiation initiated from the client side.</span></span><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333;background:#FEFDFD">Thanks and Regards,</span><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#333333;background:#FDFCFC">Sashank</span><span style="font-size:10.5pt;font-family:"-webkit-standard",serif;color:black"><o:p></o:p></span></p>
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