Network Working Group C. Huitema
Internet-Draft Private Octopus Inc.
Intended status: Informational E. Rescorla
Expires: November 21, 2018 RTFM, Inc.
May 20, 2018
Issues and Requirements for SNI Encryption in TLS
draft-ietf-tls-sni-encryption-03
Abstract
This draft describes the general problem of encryption of the Server
Name Identification (SNI) parameter. The proposed solutions hide a
Hidden Service behind a Fronting Service, only disclosing the SNI of
the Fronting Service to external observers. The draft lists known
attacks against SNI encryption, discusses the current "co-tenancy
fronting" solution, and presents requirements for future TLS layer
solutions.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 21, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Huitema & Rescorla Expires November 21, 2018 [Page 1]
Internet-Draft TLS-SNI Encryption Requirements May 2018
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. History of the TLS SNI extension . . . . . . . . . . . . . . 3
2.1. Unanticipated usage of SNI information . . . . . . . . . 3
2.2. SNI encryption timeliness . . . . . . . . . . . . . . . . 4
2.3. End-to-end alternatives . . . . . . . . . . . . . . . . . 4
3. Security and Privacy Requirements for SNI Encryption . . . . 5
3.1. Mitigate Replay Attacks . . . . . . . . . . . . . . . . . 5
3.2. Avoid Widely Shared Secrets . . . . . . . . . . . . . . . 5
3.3. Prevent SNI-based Denial of Service Attacks . . . . . . . 6
3.4. Do not stick out . . . . . . . . . . . . . . . . . . . . 6
3.5. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 6
3.6. Proper Security Context . . . . . . . . . . . . . . . . . 6
3.7. Fronting Server Spoofing . . . . . . . . . . . . . . . . 7
3.8. Supporting multiple protocols . . . . . . . . . . . . . . 7
3.8.1. Hiding the Application Layer Protocol Negotiation . . 8
3.8.2. Support other transports than HTTP . . . . . . . . . 8
3.9. Fail to fronting . . . . . . . . . . . . . . . . . . . . 8
4. HTTP Co-Tenancy Fronting . . . . . . . . . . . . . . . . . . 9
4.1. HTTPS Tunnels . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Delegation Control . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Historically, adversaries have been able to monitor the use of web
services through three channels: looking at DNS requests, looking at
IP addresses in packet headers, and looking at the data stream
between user and services. These channels are getting progressively
closed. A growing fraction of Internet communication is encrypted,
mostly using Transport Layer Security (TLS) [RFC5246]. Progressive
deployment of solutions like DNS in TLS [RFC7858] mitigates the
disclosure of DNS information. More and more services are colocated
on multiplexed servers, loosening the relation between IP address and
web service. However, multiplexed servers rely on the Service Name
Information (SNI) to direct TLS connections to the appropriate
service implementation. This protocol element is transmitted in
Huitema & Rescorla Expires November 21, 2018 [Page 2]
Internet-Draft TLS-SNI Encryption Requirements May 2018
clear text. As the other methods of monitoring get blocked,
monitoring focuses on the clear text SNI. The purpose of SNI
encryption is to prevent that.
In the past, there have been multiple attempts at defining SNI
encryption. These attempts have generally floundered, because the
simple designs fail to mitigate several of the attacks listed in
Section 3. In the absence of a TLS level solution, the most popular
approach to SNI privacy is HTTP level fronting, which we discuss in
Section 4.
2. History of the TLS SNI extension
The SNI extension was standardized in 2003 in [RFC3546] to facilitate
management of "colocation servers", in which a multiple services
shared the same IP address. A typical example would be mutiple web
sites served by the same web server. The SNI extension carries the
name of a specific server, enabling the TLS connection to be
established with the desired server context. The current SNI
extension specification can be found in [RFC6066].
The SNI specification allowed for different types of server names,
but only the "hostname" variant was standardized and deployed. In
that variant, the SNI extension carries the domain name of the target
server. The SNI extension is carried in clear text in the TLS
"Client Hello" message.
2.1. Unanticipated usage of SNI information
The SNI was defined to facilitate management of servers, but the
developer of middleboxes soon found out that they could take
advantage of the information. Many examples of such usage are
reviewed in [I-D.mm-wg-effect-encrypt]. They include:
o Censorship of specific sites by "national firewalls",
o Content filtering by ISP blocking specific web sites in order to
implement "parental controls", or to prevent access to fraudulent
web sites, such as used for phishing,
o ISP assigning different QOS profiles to target services,
o Enterprise firewalls blocking web sites not deemed appropriate for
work,
o Enterprise firewalls exempting specific web sites from MITM
inspection, such as healthcare or financial sites for which
inspection would intrude with the privacy of employees.
Huitema & Rescorla Expires November 21, 2018 [Page 3]
Internet-Draft TLS-SNI Encryption Requirements May 2018
The SNI is probably also included in the general collection of
metadata by pervasive surveillance actors.
2.2. SNI encryption timeliness
The clear-text transmission of the SNI was not flagged as a problem
in the security consideration sections of [RFC3546], [RFC4366], or
[RFC6066]. These specifications did not anticipate the abuses
described in Section 2.1. One reason may be that, when these RFCs
were written, the SNI information was available through a variety of
other means.
Many deployments still allocate different IP addresses to different
services, so that different services can be identified by their IP
addresses. However, content distribution networks (CDN) commonly
serve a large number of services through a small number of addresses.
The SNI carries the domain name of the server, which is also sent as
part of the DNS queries. Most of the SNI usage described in
Section 2.1 could also be implemented by monitoring DNS traffic or
controlling DNS usage. But this is changing with the advent of DNS
resolvers providing services like DNS over TLS [RFC7858] or DNS over
HTTPS [I-D.ietf-doh-dns-over-https].
The common name component of the server certificate generally exposes
the same name as the SNI. In TLS versions 1.0 [RFC2246], 1.1
[RFC4346], and 1.2 [RFC5246], the server send their certificate in
clear text, ensuring that there would be limited benefits in hiding
the SNI. But the transmission of the server certificate is protected
in TLS 1.3 [I-D.ietf-tls-tls13].
The decoupling of IP addresses and server names, the deployment of
DNS privacy, and the protection of server certificates transmissions
all contribute to user privacy. Encrypting the SNI now will complete
this push for privacy and make it much harder to censor specific
internet services.
2.3. End-to-end alternatives
Deploying SNI encryption will help thwarting most the "unanticipated"
SNI usages described in Section 2.1, including censorship and
pervasive surveillance. It will also thwart functions that are
sometimes described as legitimate. Most of these functions can
however be realized by other means. For example, some DNS service
providers offer customers the provision to "opt in" filtering
services for parental control and phishing protection. Per stream
QoS can be provided by a combination of packet marking and end to end
agreements. Enterprises can deploy monitoring software to control
Huitema & Rescorla Expires November 21, 2018 [Page 4]
Internet-Draft TLS-SNI Encryption Requirements May 2018
usage of the enterprises computers. As SNI encryption becomes
common, we can expect more deployment of such "end to end" solutions.
3. Security and Privacy Requirements for SNI Encryption
Over the past years, there have been multiple proposals to add an SNI
encryption option in TLS. Many of these proposals appeared
promising, but were rejected after security reviews pointed plausible
attacks. In this section, we collect a list of these known attacks.
3.1. Mitigate Replay Attacks
The simplest SNI encryption designs replace in the initial TLS
exchange the clear text SNI with an encrypted value, using a key
known to the multiplexed server. Regardless of the encryption used,
these designs can be broken by a simple replay attack, which works as
follow:
1- The user starts a TLS connection to the multiplexed server,
including an encrypted SNI value.
2- The adversary observes the exchange and copies the encrypted SNI
parameter.
3- The adversary starts its own connection to the multiplexed server,
including in its connection parameters the encrypted SNI copied from
the observed exchange.
4- The multiplexed server establishes the connection to the protected
service, thus revealing the identity of the service.
One of the goals of SNI encryption is to prevent adversaries from
knowing which Hidden Service the client is using. Successful replay
attacks breaks that goal by allowing adversaries to discover that
service.
3.2. Avoid Widely Shared Secrets
It is easy to think of simple schemes in which the SNI is encrypted
or hashed using a shared secret. This symmetric key must be known by
the multiplexed server, and by every users of the protected services.
Such schemes are thus very fragile, since the compromise of a single
user would compromise the entire set of users and protected services.
Huitema & Rescorla Expires November 21, 2018 [Page 5]
Internet-Draft TLS-SNI Encryption Requirements May 2018
3.3. Prevent SNI-based Denial of Service Attacks
Encrypting the SNI may create extra load for the multiplexed server.
Adversaries may mount denial of service attacks by generating random
encrypted SNI values and forcing the multiplexed server to spend
resources in useless decryption attempts.
It may be argued that this is not an important DOS avenue, as regular
TLS connection attempts also require the server to perform a number
of cryptographic operations. However, in many cases, the SNI
decryption will have to be performed by a front end component with
limited resources, while the TLS operations are performed by the
component dedicated to their respective services. SNI based DOS
attacks could target the front end component.
3.4. Do not stick out
In some designs, handshakes using SNI encryption can be easily
differentiated from "regular" handshakes. For example, some designs
require specific extensions in the Client Hello packets, or specific
values of the clear text SNI parameter. If adversaries can easily
detect the use of SNI encryption, they could block it, or they could
flag the users of SNI encryption for special treatment.
In the future, it might be possible to assume that a large fraction
of TLS handshakes use SNI encryption. If that was the case, the
detection of SNI encryption would be a lesser concern. However, we
have to assume that in the near future, only a small fraction of TLS
connections will use SNI encryption.
3.5. Forward Secrecy
The general concerns about forward secrecy apply to SNI encryption
just as well as to regular TLS sessions. For example, some proposed
designs rely on a public key of the multiplexed server to define the
SNI encryption key. If the corresponding private key was
compromised, the adversaries would be able to process archival
records of past connections, and retrieve the protected SNI used in
these connections. These designs failed to maintain forward secrecy
of SNI encryption.
3.6. Proper Security Context
We can design solutions in which the multiplexed server or a fronting
service act as a relay to reach the protected service. Some of those
solutions involve just one TLS handshake between the client and the
multiplexed server, or between the client and the fronting service.
Huitema & Rescorla Expires November 21, 2018 [Page 6]
Internet-Draft TLS-SNI Encryption Requirements May 2018
The master secret is verified by verifying a certificate provided by
either of these entities, but not by the protected service.
These solutions expose the client to a Man-In-The-Middle attack by
the multiplexed server or by the fronting service. Even if the
client has some reasonable trust in these services, the possibility
of MITM attack is troubling.
The multiplexed server or the fronting services could be pressured by
adversaries. By design, they could be forced to deny access to the
protected service, or to divulge which client accessed it. But if
MITM is possible, the adversaries would also be able to pressure them
into intercepting or spoofing the communications between client and
protected service.
3.7. Fronting Server Spoofing
Adversaries could mount an attack by spoofing the Fronting Service.
A spoofed Fronting Service could act as a "honeypot" for users of
hidden services. At a minimum, the fake server could record the IP
addresses of these users. If the SNI encryption solution places too
much trust on the fronting server, the fake server could also serve
fake content of its own choosing, including various forms of malware.
There are two main channels by which adversaries can conduct this
attack. Adversaries can simply try to mislead users into believing
that the honeypot is a valid Fronting Server, especially if that
information is carried by word of mouth or in unprotected DNS
records. Adversaries can also attempt to hijack the traffic to the
regular Fronting Server, using for example spoofed DNS responses or
spoofed IP level routing, combined with a spoofed certificate.
3.8. Supporting multiple protocols
The SNI encryption requirement do not stop with HTTP over TLS.
Multiple other applications currently use TLS, including for example
SMTP [RFC5246], DNS [RFC7858], or XMPP [RFC7590]. These applications
too will benefit of SNI encryption. HTTP only methods like those
described in Section 4.1 would not apply there. In fact, even for
the HTTPS case, the HTTPS tunneling service described in Section 4.1
is compatible with HTTP 1.0 and HTTP 1.1, but interacts awkwardly
with the multiple streams feature of HTTP 2.0 [RFC7540]. This points
to the need of an application agnostic solution, that would be
implemented fully in the TLS layer.
Huitema & Rescorla Expires November 21, 2018 [Page 7]
Internet-Draft TLS-SNI Encryption Requirements May 2018
3.8.1. Hiding the Application Layer Protocol Negotiation
The Application Layer Protocol Negotiation (ALPN) parameters of TLS
allow implementations to negotiate the application layer protocol
used on a given connection. TLS provides the ALPN values in clear
text during the initial handshake. While exposing the ALPN does not
create the same privacy issues as exposing the SNI, there is still a
risk. For example, some networks may attempt to block applications
that they do not understand, or that they wish users would not use.
In a sense, ALPN filtering could be very similar to the filtering of
specific port numbers exposed in some network. This filtering by
ports has given rise to evasion tactics in which various protocols
are tunneled over HTTP in order to use open ports 80 or 443.
Filtering by ALPN would probably beget the same responses, in which
the applications just move over HTTP, and only the HTTP ALPN values
are used. Applications would not need to do that if the ALPN was
hidden in the same way as the SNI.
It is thus desirable that SNI Encryption mechanisms be also able hide
the ALPN.
3.8.2. Support other transports than HTTP
The TLS handshake is also used over other transports such as UDP with
both DTLS [I-D.ietf-tls-dtls13] and QUIC [I-D.ietf-quic-tls]. The
requirement to encrypt the SNI apply just as well for these
transports as for TLS over TCP.
This points to a requirement for SNI Encryption mechanisms to also be
applicable to non-TCP transports such as DTLS or QUIC.
3.9. Fail to fronting
It is easy to imagine designs in which the client sends some client
hello extension that points to a secret shared by client and hidden
server. If that secret is incorporated into the handshake secret,
the exchange will only succeeds if the connection truly ends at the
hidden server. The exchange will fail if the extension is stripped
by an MITM, and the exchange will also fail if an adversary replays
the extension in a Client Hello.
The problem with that approach is clear. Adversaries that replay the
extension can test whether the client truly wanted to access the
fronting server, or was simply using that fronting server as an
access gateway to something else. The adversaries will not know what
hidden service the client was trying to reach, but they can guess.
Huitema & Rescorla Expires November 21, 2018 [Page 8]
Internet-Draft TLS-SNI Encryption Requirements May 2018
They can also start directly interrogate the user, or other
unpleasant alternatives.
When designing SNI encryption schemes, we have to take into account
attacks that strip parameters from the Client Hello, or replay
attacks. In both cases, the desired behavior is to fall back to a
connection with the fronting server, so there is no visble difference
between a regular connection to that server and an attempt to reach
the hidden server.
4. HTTP Co-Tenancy Fronting
In the absence of TLS level SNI encryption, many sites rely on an
"HTTP Co-Tenancy" solution. The TLS connection is established with
the fronting server, and HTTP requests are then sent over that
connection to the hidden service. For example, the TLS SNI could be
set to "fronting.example.com", the fronting server, and HTTP requests
sent over that connection could be directed to "hidden.example.com/
some-content", accessing the hidden service. This solution works
well in practice when the fronting server and the hidden server are
'co-tenant" of the same multiplexed server.
The HTTP fronting solution can be deployed without modification to
the TLS protocol, and does not require using any specific version of
TLS. There are however a few issues regarding discovery, client
implementations, trust, and applicability:
o The client has to discover that the hidden service can be accessed
through the fronting server.
o The client browser's has to be directed to access the hidden
service through the fronting service.
o Since the TLS connection is established with the fronting service,
the client has no proof that the content does in fact come from
the hidden service. The solution does thus not mitigate the
context sharing issues described in Section 3.6.
o Since this is an HTTP level solution, it would not protected non
HTTP protocols such as DNS over TLS [RFC7858] or IMAP over TLS
[RFC2595].
The discovery issue is common to pretty much every SNI encryption
solution. The browser issue may be solved by developing a browser
extension that support HTTP Fronting, and manages the list of
fronting services associated with the hidden services that the client
uses. The multi-protocol issue can be mitigated by using
implementation of other applications over HTTP, such as for example
Huitema & Rescorla Expires November 21, 2018 [Page 9]
Internet-Draft TLS-SNI Encryption Requirements May 2018
DNS over HTTPS [I-D.hoffman-dns-over-https]. The trust issue,
however, requires specific developments.
4.1. HTTPS Tunnels
The HTTP Fronting solution places a lot of trust in the Fronting
Server. This required trust can be reduced by tunnelling HTTPS in
HTTPS, which effectively treats the Fronting Server as an HTTP Proxy.
In this solution, the client establishes a TLS connection to the
Fronting Server, and then issues an HTTP Connect request to the
Hidden Server. This will establish an end-to-end HTTPS over TLS
connection between the client and the Hidden Server, mitigating the
issues described in Section 3.6.
The HTTPS in HTTPS solution requires double encryption of every
packet. It also requires that the fronting server decrypts and relay
messages to the hidden server. Both of these requirements make the
implementation onerous.
4.2. Delegation Control
Clients would see their privacy compromised if they contacted the
wrong fronting server to access the hidden service, since this wrong
server could disclose their access to adversaries. This requires a
controlled way to indicate which fronting ferver is acceptable by the
hidden service.
This problem is both similar and different from the "fronting server
spoofing" attack described in Section 3.7. Here, the spoofing would
be performed by distributing fake advice, such as "to reach example
hidden.example.com, use fake.example.com as a fronting server", when
"fake.example.com" is under the control of an adversary.
In practice, this attack is well mitigated when the hidden service is
accessed through a specialized application. The name of the fronting
server can then be programmed in the code of the application. But
the attack is much harder to mitigate when the hidden service has to
be accessed through general purpose web browsers. The browsers will
need a mechanism to obtain the fronting server indication in a secure
way.
There are several proposed solutions to this problem, such as
creating a special form of certificate to codify the relation between
fronting and hidden server, or obtaining the relation between hidden
and fronting service through the DNS, possibly using DNSSEC to avoid
spoofing.
Huitema & Rescorla Expires November 21, 2018 [Page 10]
Internet-Draft TLS-SNI Encryption Requirements May 2018
We can observe that content distribution network have a similar
requirement. They need to convince the client that "www.example.com"
can be accessed through the seemingly unrelated "cdn-node-
xyz.example.net". Most CDN have deployed DNS-based solutions to this
problem.
5. Security Considerations
Replacing clear text SNI transmission by an encrypted variant will
improve the privacy and reliability of TLS connections, but the
design of proper SNI encryption solutions is difficult. This
document does not present the design of a solution, but provide
guidelines for evaluating proposed solutions.
This document lists a number of attacks against SNI encryption in
Section 3, and also in Section 4.2, and presents a list of
requirements to mitigate these attacks. The current HTTP based
solutions described in Section 4 only meet some of these
requirements. In practice, it may well be that no solution can meet
every requirement, and that practical solutions will have to make
some compromises.
In particular, the requirement to not stick out presented in
Section 3.4 may have to be lifted, especially if for proposed
solutions that could quickly reach large scale deployments.
6. IANA Considerations
This draft does not require any IANA action.
7. Acknowledgements
A large part of this draft originates in discussion of SNI encryption
on the TLS WG mailing list, including comments after the tunneling
approach was first proposed in a message to that list:
<https://mailarchive.ietf.org/arch/msg/tls/
tXvdcqnogZgqmdfCugrV8M90Ftw>.
Thanks to Daniel Kahn Gillmor for a pretty detailed review of the
initial draft.
8. References
8.1. Normative References
Huitema & Rescorla Expires November 21, 2018 [Page 11]
Internet-Draft TLS-SNI Encryption Requirements May 2018
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
March 2018.
8.2. Informative References
[I-D.hoffman-dns-over-https]
Hoffman, P. and P. McManus, "DNS Queries over HTTPS",
draft-hoffman-dns-over-https-01 (work in progress), June
2017.
[I-D.ietf-doh-dns-over-https]
Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DOH)", draft-ietf-doh-dns-over-https-08 (work in
progress), May 2018.
[I-D.ietf-quic-tls]
Thomson, M. and S. Turner, "Using Transport Layer Security
(TLS) to Secure QUIC", draft-ietf-quic-tls-11 (work in
progress), April 2018.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-26 (work in progress), March
2018.
[I-D.mm-wg-effect-encrypt]
Moriarty, K. and A. Morton, "Effects of Pervasive
Encryption on Operators", draft-mm-wg-effect-encrypt-25
(work in progress), March 2018.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, DOI 10.17487/RFC2246, January 1999,
<https://www.rfc-editor.org/info/rfc2246>.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999,
<https://www.rfc-editor.org/info/rfc2595>.
[RFC3546] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 3546, DOI 10.17487/RFC3546, June 2003,
<https://www.rfc-editor.org/info/rfc3546>.
Huitema & Rescorla Expires November 21, 2018 [Page 12]
Internet-Draft TLS-SNI Encryption Requirements May 2018
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346,
DOI 10.17487/RFC4346, April 2006,
<https://www.rfc-editor.org/info/rfc4346>.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, DOI 10.17487/RFC4366, April 2006,
<https://www.rfc-editor.org/info/rfc4366>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7590] Saint-Andre, P. and T. Alkemade, "Use of Transport Layer
Security (TLS) in the Extensible Messaging and Presence
Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June
2015, <https://www.rfc-editor.org/info/rfc7590>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
Authors' Addresses
Christian Huitema
Private Octopus Inc.
Friday Harbor WA 98250
U.S.A
Email: huitema@huitema.net
Huitema & Rescorla Expires November 21, 2018 [Page 13]
Internet-Draft TLS-SNI Encryption Requirements May 2018
Eric Rescorla
RTFM, Inc.
U.S.A
Email: ekr@rtfm.com
Huitema & Rescorla Expires November 21, 2018 [Page 14]
