Re: [TLS] SNI from CDN to Origin (was I-D Action: draft-ietf-tls-sni-encryption-08.txt)

"Salz, Rich" <> Thu, 10 October 2019 15:53 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id AB2A11202DD for <>; Thu, 10 Oct 2019 08:53:21 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.7
X-Spam-Status: No, score=-2.7 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id m4YEvuZdA3H1 for <>; Thu, 10 Oct 2019 08:53:19 -0700 (PDT)
Received: from ( [IPv6:2620:100:9005:57f::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 8499A120802 for <>; Thu, 10 Oct 2019 08:53:19 -0700 (PDT)
Received: from pps.filterd ( []) by ( with SMTP id x9AFqfNv031195; Thu, 10 Oct 2019 16:53:17 +0100
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; h=from : to : cc : subject : date : message-id : references : in-reply-to : content-type : mime-version; s=jan2016.eng; bh=F+tZWFW+1S0HtuPGaN4jQ3wokvGe66/OYu3uZDcKur4=; b=X7DEntlcWGU8GF/RKPXe2JdAg8rLEmHj/L2VcW7QxJ9/u6lNwZy1P1+1Z9e7NypVUFu3 hfbWkKRQsMspWp0g8n9QuUInusbaioczQEHw3V/MC2jR7qTCu5bTKbb2hOzg79UVG9QE menIGr4ptCsDLFzozv94zQmxFYDkASSYStvOn6mMKOaqueIk2HaYC5f2ETnTEO1p5ID0 QbRknvqlf28ra1ytKiI1goDTo2unkeUCNWMQjFFVEdp7XMt72/rtbqtcSazHleYjltY9 su3an8sKk3aesC6BNfTnj7yn8BTec2Df2/GBP4Bfvg39YLI35KhN44vwrXNB5WOwehXO Sw==
Received: from prod-mail-ppoint7 ( [] (may be forged)) by with ESMTP id 2veg1u1dbv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 10 Oct 2019 16:53:17 +0100
Received: from pps.filterd ( []) by ( with SMTP id x9AFmDoW008191; Thu, 10 Oct 2019 11:53:16 -0400
Received: from ([]) by with ESMTP id 2veph0pf4c-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA384 bits=256 verify=NOT); Thu, 10 Oct 2019 11:53:15 -0400
Received: from ( by ( with Microsoft SMTP Server (TLS) id 15.0.1473.3; Thu, 10 Oct 2019 10:53:14 -0500
Received: from ([]) by ([]) with mapi id 15.00.1473.005; Thu, 10 Oct 2019 10:53:14 -0500
From: "Salz, Rich" <>
To: Rob Sayre <>, Eric Rescorla <>
CC: "" <>
Thread-Topic: [TLS] SNI from CDN to Origin (was I-D Action: draft-ietf-tls-sni-encryption-08.txt)
Date: Thu, 10 Oct 2019 15:53:14 +0000
Message-ID: <>
References: <> <> <> <> <> <> <> <> <> <> <> <> <> <>
In-Reply-To: <>
Accept-Language: en-US
Content-Language: en-US
user-agent: Microsoft-MacOutlook/10.1e.0.191003
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: []
Content-Type: multipart/alternative; boundary="_000_7F634AD9590941B0AB08D6FA6AB0C816akamaicom_"
MIME-Version: 1.0
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-10-10_05:, , signatures=0
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910100145
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,1.0.8 definitions=2019-10-10_05:2019-10-10,2019-10-10 signatures=0
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 phishscore=0 impostorscore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 priorityscore=1501 mlxlogscore=999 mlxscore=0 adultscore=0 bulkscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1910100146
Archived-At: <>
Subject: Re: [TLS] SNI from CDN to Origin (was I-D Action: draft-ietf-tls-sni-encryption-08.txt)
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "This is the mailing list for the Transport Layer Security working group of the IETF." <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Thu, 10 Oct 2019 15:53:33 -0000

  *   I want to keep the SNI encrypted in TLS hops that use client certificates, but where ESNI won't work.

I have some questions about this, see below.

  *   For example, how is the SNI transmitted in the parens here:

  *   [ Client ] -----> (ESNI) -----> [ CDN ] -----> (???) -----> [ Origin ]

It is transmitted in the clear.  There is no architectural reason why it could not be ESNI.  But in my experience, there’s not much point in it, either.

What do you mean by client cert?  The CDN->Origin hop cannot present original Client’s certificate because (in general, maybe there are some exceptions) the CDN does not have the private key so it cannot do the necessary crypto operations.  That’s the right thing to do, otherwise anyone could present any client cert and claim to be the Client.  Instead, the Client certificate (or parts of it such as the subjectDN) are presented in newly-added HTTP headers.  The origin is configured to trust those headers, depending on the CDN/Origin relationship – it could be the CDN has it’s own client cert, it could be via IP filters, etc.

  *   I don't think a DNS-based solution like ESNI will work for that second hop, because the origin tends to be identified by an IP address rather than a domain name.

In our experience, the origin is identified by a DNS name.  I could double-check, but I don’t think *any* of our customer origins are identified by IP address.