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draft-reddy-dprive-bootstrap-dns-server-00.xml
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draft-reddy-dprive-bootstrap-dns-server-00.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-reddy-dprive-bootstrap-dns-server-00"
ipr="trust200902">
<front>
<title abbrev="DoT/DoH server discovery">A Bootstrapping Procedure to
Discover and Authenticate DNS-over-(D)TLS and DNS-over-HTTPS
Servers</title>
<author fullname="Tirumaleswar Reddy" initials="T." surname="Reddy">
<organization abbrev="McAfee">McAfee, Inc.</organization>
<address>
<postal>
<street>Embassy Golf Link Business Park</street>
<city>Bangalore</city>
<region>Karnataka</region>
<code>560071</code>
<country>India</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Dan Wing" initials="D." surname="Wing">
<organization></organization>
<address>
<postal>
<street></street>
<country>USA</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Michael C. Richardson" initials="M."
surname="Richardson">
<organization>Sandelman Software Works</organization>
<address>
<postal>
<street></street>
<country>USA</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Mohamed Boucadair" initials="M." surname="Boucadair">
<organization>Orange</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<date day="21" month="February" year="2019" />
<workgroup>DPRIVE WG</workgroup>
<abstract>
<t>This document specifies mechanisms to automatically bootstrap
endpoints (e.g., hosts, Customer Equipment) to discover and authenticate
DNS-over-(D)TLS and DNS-over-HTTPS servers provided by a local
network.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>Various network security services are provided by Enterprise, secure
home and wall-gardened networks to protect endpoints (e.g,. hosts, IoT
devices). Some of these security services act on DNS requests from
endpoints. However, if an endpoint is configured to use public
DNS-over-(D)TLS <xref target="RFC7858"></xref> <xref
target="RFC8094"></xref> or DNS-over-HTTPS <xref
target="RFC8484"></xref> servers, network security services in the local
network cannot act efficiently on DNS requests from the endpoints. In
order to act on DNS requests from endpoints, network security services
can block DNS-over-(D)TLS traffic by dropping outgoing packets to
destination port 853, and by identifying the domains offering
DNS-over-HTTPS servers, DNS-over-HTTPS traffic can be blocked by
dropping outgoing packets to these domains. If the endpoint has enabled
strict privacy profile (Section 5 of <xref target="RFC8310"></xref>),
and the network security service blocks the traffic to the public DNS
server, DNS service is not available to the endpoint and ultimately the
endpoint cannot access Internet. If the endpoint has enabled
opportunistic privacy profile (Section 5 of <xref
target="RFC8310"></xref>), and the network security service blocks
traffic to the public DNS server, the endpoint will either fallback to
an encrypted connection without authenticating the DNS-over-(D)TLS and
DNS-over-HTTPS servers provided by the local network or fallback to
clear text DNS, and cannot exchange encrypted DNS messages. This can
compromise the endpoint security and privacy; some of the potential
security threats are listed below:</t>
<t><list style="symbols">
<t>Pervasive monitoring of DNS traffic.</t>
<t>If the endpoint is an IoT device which is configured to use
public DNS-over-(D)TLS or DNS-over-HTTPS servers, and if a policy
enforcement point in the local network is programmed using a
Manufacturer Usage Description (MUD) file <xref
target="I-D.ietf-opsawg-mud"></xref> by a MUD manager to only allow
intented communications to and from the IoT device, the policy
enforcement point cannot enforce the Network Access Control List
rules based on domain names (Section 8 of <xref
target="I-D.ietf-opsawg-mud"></xref>).</t>
<t>The network security service cannot prevent an endpoint from
accessing malicious domains. Attacks like DNS cache poisoning can
lead the user to visit malicious website to inject malware on the
endpoint. For instance, malwares like DNSChanger can modify the
endpoint's DNS entries to point toward its own rogue name servers
which then injected its own advertising into Web pages.</t>
</list></t>
<t>The DPRIVE and DoH working groups have not defined an automated
mechanism to securely bootstrap the endpoints to discover and
authenticate DNS-over-(D)TLS and DNS-over-HTTPS servers in the local
network. Some clients have hard-coded specific public DNS servers (such
as Mozilla using Cloudflare's DNS-over-HTTPS server). If endpoints
continue to use hard-coded public DNS servers, this has a risk of
relying on few centralized DNS services. Further, Content Delivery
Networks (CDNs) that map traffic based on DNS may lose the ability to
direct end-user traffic to a nearby cluster in cases where a DNS service
is being used that is not affiliated with the local network and which
does not send "EDNS Client Subnet" (ECS) information to the CDN's DNS
authorities <xref target="CDN"></xref>.</t>
<t>The document proposes a mechanism to automatically bootstrap the
endpoints to discover and authenticate the DNS-over-(D)TLS and
DNS-over-HTTPS servers provided by the local network. The overall
procedure can be structured into the following steps:<list
style="symbols">
<t>Bootstrapping phase (<xref target="bootstrap-iot"></xref> and
<xref target="bootstrap-endpoint"> </xref>) is meant to
automatically to automatically bootstrap endpoints with local
network's CA certificates and DNS server certificate.</t>
<t>Discovery phase (<xref target="discovery"></xref>) is meant to
discover an authentication domain (defined in <xref
target="RFC8310"></xref>) to authenticate the privacy-enabling DNS
server, the privacy-enabling protocols supported by the DNS server
and usable DNS server IP addresses. </t>
<t>Connection handshake and service invocation: The DNS client
initiates (D)TLS handshake with the DNS server learned in the
discovery phase. Furthermore, DNS client uses the credentials
discovered during the bootstrapping phase to validate the server
certificate.</t>
</list></t>
<t>This document uses the terms defined in <xref
target="RFC8499"></xref>.</t>
</section>
<section title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP 14
<xref target="RFC2119"></xref><xref target="RFC8174"></xref> when, and
only when, they appear in all capitals, as shown here.</t>
</section>
<section anchor="bootstrap-iot" title="Bootstrapping IoT Devices and CPE">
<t>The following steps discuss the mechanism to automatically bootstrap
IoT devices with local network's CA certificates and DNS server
certificate. The below steps can also be used by CPE acting as DNS
forwarders to discover and authenticate DNS-over-(D)TLS and
DNS-over-HTTPS servers provided by the access networks.<list
style="symbols">
<t>The IoT device can use Bootstrapping Remote Secure Key
Infrastructures (BRSKI) discussed in <xref
target="I-D.ietf-anima-bootstrapping-keyinfra"></xref> to
automatically bootstrap the IoT device using the IoT manufacturer
provisioned X.509 certificate, in combination with a registrar
provided by the local network and IoT device manufacturer's
authorizing service (MASA). <list style="numbers">
<t>The IoT device authenticates to the local network using the
IoT manufacturer provisioned X.509 certificate. The IoT device
can request and get a voucher from the MASA service via the
registrar. The voucher is signed by the MASA service and
includes the local network's CA public key.</t>
<t>The IoT device validates the signed voucher using the
manufacturer installed trust anchor associated with the MASA,
stores the CA's public key and validates the provisional TLS
connection to the registrar.</t>
<t>The IoT device requests the full Enrollment over Secure
Transport (EST) <xref target="RFC7030"></xref> distribution of
current CA certificates (Section 5.9.1 in <xref
target="I-D.ietf-anima-bootstrapping-keyinfra"></xref>) from the
registrar operating as a BRSKI-EST server. The IoT device uses
the Explicit Trust Anchor database to validate the DNS server
certificate.</t>
<t>TBD: The IoT device learns the End-Entity certificates <xref
target="RFC8295"></xref> from the BRSKI-EST server. The
certificate provisioned to the DNS server in the local network
will be treated as a End-Entity certificate. The IoT device
needs to identify the End-Entity certificate is provisioned to
the DNS server, the key usage extension <xref
target="RFC5280"></xref> can be used to restrict the use of the
End-Entity certificate to authenticate the DNS server, a new bit
will be added to the KeyUsage type to identify the DNS server
certificate.</t>
</list></t>
</list></t>
</section>
<section anchor="bootstrap-endpoint"
title="Bootstrapping Endpoint Devices">
<t>The following steps explain the mechanism to automatically bootstrap
an endpoint with the local network's CA certificates and DNS server
certificate: <list style="numbers">
<t>The endpoint authenticates to the local network and establishes
provisional TLS connection with the registrar operating as the
BRSKI-EST server. The endpoint discovers registrar using DNS-based
Service Discovery <xref target="RFC6763"></xref>.</t>
<t>The endpoint uses Salted Challenge Response Authentication
Mechanism (SCRAM) <xref target="RFC7804"></xref> to perform mutual
authentication with the discovered BRSKI-EST server.</t>
<t>If the BRSKI-EST server authentication is successful, the
endpoint requests the full EST distribution of current CA
certificates and validates the provisional TLS connection to the
BRSKI-EST server. If the BRSKI-EST server certificate cannot be
verified using the CA certificates downloaded, the TLS connection is
immediately discarded and the endpoint abandons the attempt to
bootstrap from the BRSKI-EST server and discards the CA certificates
conveyed by the BRSKI-EST server. The endpoint uses the Explicit
Trust Anchor database to validate the DNS server certificate.</t>
<t>TBD: The endpoint learns the End-Entity certificates <xref
target="RFC8295"></xref> from the BRSKI-EST server. The certificate
provisioned to the DNS server in the local network will be treated
as a End-Entity certificate. The endpoint needs to identify the
End-Entity certificate is provisioned to the DNS server, the key
usage extension <xref target="RFC5280"></xref> can be used to
restrict the use of the End-Entity certificate to authenticate the
DNS server, a new bit will be added to the KeyUsage type to identify
the DNS server certificate.</t>
</list></t>
</section>
<section anchor="discovery" title="Discovery Procedure">
<t>A DNS client discovers the DNS server in the local network supporting
DNS-over-TLS, DNS-over-DTLS and DNS-over-HTTPS protocols by using the
following discovery mechanism:</t>
<t><list style="symbols">
<t>The DNS client uses DHCP to discover the authentication domain
name for the DNS server, as specified in <xref
target="dhcp"></xref>.</t>
<t>The DNS client then uses S-NAPTR <xref target="RFC3958"></xref>
lookup to learn the protocols DNS-over-TLS, DNS-over-DTLS, and
DNS-over-HTTPS supported by the DNS server and the DNS privacy
protocol preferred by the DNS server administrators, as specified in
<xref target="srvr"></xref> and <xref target="serviceT"> </xref>. If
DNS-over-HTTPS protocol is supported by the DNS server, the DNS
client queries for the URI resource record type <xref
target="RFC7553"></xref> to use the https URI scheme (Section 3 of
<xref target="RFC8484"></xref>). </t>
<t>The DNS client initiates (D)TLS handshake with the DNS server,
the server presents its certificate and the client validates the
server certificate using the End-Entity certificate and Explicit
Trust Anchor database downloaded in steps 3 and 4 in <xref
target="bootstrap-iot"></xref> and <xref
target="bootstrap-endpoint"></xref>. The DNS client uses validation
techniques as described in <xref target="RFC6125"></xref> to compare
the authentication domain name to the certificate provided by the
DNS server.</t>
<t>If the DNS client cannot reach or establish an authenticated and
encrypted connection with the privacy-enabling DNS server provided
by the local network, the DNS client can fallback to the
privacy-enabling public DNS server.</t>
</list></t>
<section anchor="dhcp" title="DNS Reference Identifier DHCP Options">
<t>As reported in Section 1.7.2 of <xref
target="RFC6125"></xref>:<list style="empty">
<t>"few certification authorities issue server certificates based
on IP addresses, but preliminary evidence indicates that such
certificates are a very small percentage (less than 1%) of issued
certificates".</t>
</list></t>
<t>In order to allow for certificate authentication between a DNS
client and server while accommodating for the current best practices
for issuing certificates, this document allows for configuring
authentication domain name to clients. This name can be used as a
reference identifier for authentication purposes.</t>
<section title="DHCPv6 DNS Reference Identifier Option">
<section title="Option Format ">
<t>The DHCPv6 DNS Reference Identifier option is used to configure
an authentication domain name. The format of this option is shown
in <xref target="ri_option1"></xref>.</t>
<t><figure anchor="ri_option1"
title="DHCPv6 DNS Reference Identifier option">
<artwork><![CDATA[ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_V6_AUTH_DOMAIN | Option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| authentication-domain-name (FQDN) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>The fields of the option shown in <xref
target="ri_option1"></xref> are as follows:<?rfc subcompact="yes" ?></t>
<t><list style="symbols">
<t>Option-code: OPTION_V6_AUTH_DOMAIN (TBA1, see <xref
target="iana6"></xref>)</t>
<t>Option-length: Length of the authentication-domain-name
field in octets.</t>
<t>authentication-domain-name: A fully qualified domain name
of the DNS server. This field is formatted as specified in
Section 10 of <xref target="RFC8415"></xref>.</t>
</list></t>
</section>
<section title="DHCPv6 Client Behavior">
<t>DHCP clients MAY request options OPTION_V6_AUTH_DOMAIN as
defined in <xref target="RFC8415"></xref>, Sections 18.2.1,
18.2.2, 18.2.4, 18.2.5, 18.2.6, and 21.7. As a convenience to the
reader, it is mentioned here that the DHCP client includes the
requested option code in the Option Request Option.</t>
<t>If the DHCP client receives more than one instance of
OPTION_V6_AUTH_DOMAIN option, it MUST use only the first instance
of that option.</t>
</section>
</section>
<section title="DHCPv4 DNS Reference Identifier Option">
<section title="Option Format">
<t>The DHCPv4 DNS Reference Identifier option is used to configure
an authentication domain name. The format of this option is
illustrated in <xref target="dhcpri_dots"></xref>.</t>
<t><figure anchor="dhcpri_dots"
title="DHCPv4 DNS Reference Identifier option">
<artwork><![CDATA[
Code Length authentication domain name
+-----+-----+-----+-----+-----+-----+-----+--
|TBA2 | n | s1 | s2 | s3 | s4 | s5 | ...
+-----+-----+-----+-----+-----+-----+-----+--
The values s1, s2, s3, etc. represent the domain name labels in the
domain name encoding.
]]></artwork>
</figure></t>
<t>The fields of the option shown in <xref
target="dhcpri_dots"></xref> are as follows:<?rfc subcompact="yes" ?><list
style="symbols">
<t>Code: OPTION_V4_AUTH_DOMAIN (TBA2, see <xref
target="iana4"></xref>);</t>
<t>Length: Includes the length of the authentication domain
name field in octets; the maximum length is 255 octets.</t>
<t>Authentication domain name: The domain name of the DNS
server. This field is formatted as specified in Section 10 of
<xref target="RFC8415"></xref>.</t>
</list></t>
</section>
<section title="DHCPv4 Client Behavior">
<t>To discover a authentication domain name, the DHCPv4 client
MUST include OPTION_V4_AUTH_DOMAIN in a Parameter Request List
Option <xref target="RFC2132"></xref>.</t>
<t>If the DHCP client receives more than one instance of
OPTION_V4_AUTH_DOMAIN option, it MUST use only the first instance
of that option. The content of OPTION_V4_AUTH_DOMAIN is used as
reference identifier for authentication purposes.</t>
</section>
</section>
</section>
<section anchor="srvr" title="Resolution">
<t>Once the DNS client has retrieved the authentication domain name
for the DNS server, an S-NAPTR lookup with 'DPRIVE' application
service and the desired protocol tag is made to obtain information
necessary to securely connect to the DNS server. The S-NAPTR lookup is
performed using an untrusted recursive DNS resolver from an untrusted
source (such as DHCP). </t>
<t>This specification defines "DPRIVE" as an application service tag
(<xref target="serviceT"></xref>) and "dns.tls" (<xref
target="dnstls"></xref>), "dns.dtls" (<xref target="dnsdtls"></xref>),
and "dns.https" (<xref target="dnshttps"></xref>) as application
protocol tags.</t>
<t>If no DNS-specific S-NAPTR records can be retrieved, the discovery
procedure fails for this authentication domain name. However, before
retrying a lookup that has failed, a DNS client MUST wait a time
period that is appropriate for the encountered error (e.g., NXDOMAIN,
timeout, etc.).</t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>The bootstrapping procedure to discover and authenticate
DNS-over-(D)TLS and DNS-over-HTTPS Servers MUST be enabled by the
endpoint in a trusted network (e.g. Enterprise, Secure home networks)
and disabled in a untrusted network (e.g. public WiFi network), similar
to the way VPN connection from the endpoint to a VPN gateway is
disconnected in a trusted network and VPN connection is established in a
untrusted network. </t>
<t>The primary attack against the methods described in <xref
target="discovery"></xref> is one that would lead to impersonation of a
DNS server. An attacker could attempt to compromise the DHCP discovery
and S-NAPTR resolution. The attack is prevented by validating the
certificate presented by the DNS server. DHCP-related security
considerations are discussed in <xref target="RFC2131"></xref> and <xref
target="RFC8415"></xref>.</t>
<t>Security considerations in <xref
target="I-D.ietf-anima-bootstrapping-keyinfra"></xref> and <xref
target="RFC7804"></xref> need to be taken into consideration.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<section anchor="iana6" title="DHCPv6 Option">
<t>IANA is requested to assign the following new DHCPv6 Option Code in
the registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters:</t>
<texttable style="headers">
<ttcol align="right">Option Name</ttcol>
<ttcol>Value</ttcol>
<c>OPTION_V6_AUTH_DOMAIN</c>
<c>TBA1</c>
</texttable>
</section>
<section anchor="iana4" title="DHCPv4 Option">
<t>IANA is requested to assign the following new DHCPv4 Option Code in
the registry maintained in
http://www.iana.org/assignments/bootp-dhcp-parameters/:</t>
<texttable style="headers">
<ttcol align="right">Option Name</ttcol>
<ttcol>Value</ttcol>
<ttcol>Data length</ttcol>
<ttcol>Meaning</ttcol>
<c>OPTION_V4_AUTH_DOMAIN</c>
<c>TBA2</c>
<c>Variable; the maximum length is 255 octets.</c>
<c>Includes the authentication domain name.</c>
</texttable>
</section>
<section title="Application Service & Application Protocol Tags">
<t>This document requests IANA to make the following allocations from
the registry available at:
https://www.iana.org/assignments/s-naptr-parameters/s-naptr-parameters.xhtml.</t>
<section anchor="serviceT"
title="DNS Application Service Tag Registration">
<t><list style="symbols">
<t>Application Protocol Tag: DPRIVE</t>
<t>Intended Usage: See <xref target="srvr"></xref></t>
<t>Security Considerations: See <xref
target="Security"></xref></t>
<t>Contact Information: <one of the authors></t>
</list></t>
</section>
<section anchor="dnstls"
title="dns.tls Application Protocol Tag Registration">
<t><list style="symbols">
<t>Application Protocol Tag: dns.tls</t>
<t>Intended Usage: See <xref target="srvr"></xref></t>
<t>Security Considerations: See <xref
target="Security"></xref></t>
<t>Contact Information: <one of the authors></t>
</list></t>
</section>
<section anchor="dnsdtls"
title="dns.dtls Application Protocol Tag Registration">
<t><list style="symbols">
<t>Application Protocol Tag: dns.dtls</t>
<t>Intended Usage: See <xref target="srvr"></xref></t>
<t>Security Considerations: See <xref
target="Security"></xref></t>
<t>Contact Information: <one of the authors></t>
</list></t>
</section>
<section anchor="dnshttps"
title="dns.https Application Protocol Tag Registration">
<t><list style="symbols">
<t>Application Protocol Tag: dnshttps</t>
<t>Intended Usage: See <xref target="srvr"></xref></t>
<t>Security Considerations: See <xref
target="Security"></xref></t>
<t>Contact Information: <one of the authors></t>
</list></t>
</section>
</section>
</section>
<section anchor="acknowledgments" title="Acknowledgments">
<t>Thanks to Joe Hildebrand for his comments and suggestions.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.8415"?>
<?rfc include="reference.RFC.2119"?>
<?rfc include='reference.RFC.8174'?>
<?rfc include="reference.RFC.6125"?>
<?rfc include="reference.RFC.2132"?>
<?rfc include='reference.RFC.2131'?>
<?rfc include="reference.RFC.7030"?>
<?rfc include="reference.RFC.8295"?>
<?rfc include="reference.RFC.5280"?>
<?rfc include="reference.RFC.7804"?>
<?rfc include="reference.RFC.8484"?>
<?rfc include="reference.RFC.7858"?>
<?rfc include="reference.RFC.8094"?>
<?rfc include="reference.RFC.3958"?>
<?rfc include="reference.RFC.6763"?>
<?rfc include="reference.RFC.7553"?>
<?rfc include='reference.I-D.ietf-anima-bootstrapping-keyinfra'?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.8310"?>
<?rfc include='reference.I-D.ietf-opsawg-mud'?>
<?rfc include='reference.RFC.8499'?>
<reference anchor="CDN"
target="https://conferences.sigcomm.org/sigcomm/2015/pdf/papers/p167.pdf">
<front>
<title>End-User Mapping: Next Generation Request Routing for Content
Delivery</title>
<author>
<organization></organization>
</author>
<date year="2015" />
</front>
</reference>
</references>
</back>
</rfc>