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DNSOP WG                                                        T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                                 N. Cook
Expires: April 16, 2021                                     Open-Xchange
                                                                 D. Wing
                                                                  Citrix
                                                            M. Boucadair
                                                                  Orange
                                                        October 13, 2020


                      DNS Access Denied Error page
                    draft-reddy-dnsop-error-page-05

Abstract

   When a DNS server filters a query, the response conveys no detailed
   explanation of why that query was blocked, leading thus to end-user
   confusion.  A solution is needed to enhance the user experience.

   This document defines a method to return an URI that explains the
   reason why a DNS query was filtered.

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 April 16, 2021.

Copyright Notice

   Copyright (c) 2020 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



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   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
   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Error page URI EDNS0 option format  . . . . . . . . . . . . .   5
   4.  Error page URI Processing . . . . . . . . . . . . . . . . . .   7
   5.  Sign and Verify . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  ERROR Page  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Usability Considerations  . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  A New Error Page URI EDNS Option  . . . . . . . . . . . .  12
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   DNS filters are deployed for a variety of reasons including endpoint
   security, parental filtering, and filtering required by law
   enforcement.  These are discussed in more detail below:

   o  Various network security services are provided by Enterprise
      networks to protect endpoints (e.g., Hosts including IoT devices).
      Network-based security solutions such as firewalls and Intrusion
      Prevention Systems (IPS) rely on network traffic inspection to
      implement perimeter-based security policies.  The network security
      services may, for example, prevent malware download, block known
      malicious domains, block phishing sites, etc.  These network
      security services act on DNS queries originating from endpoints.
      For example, DNS firewalls, a method of expressing DNS response
      policy information inside specially constructed DNS zones, known
      as Response Policy Zones (RPZs) allows DNS servers to modify DNS
      responses in real time to stop access to malware and phishing
      domains.  Note that some of the commonly known types of malware
      are viruses, worms, trojans, bots, ransomware, backdoors, spyware,
      and adware.





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   o  Network devices in a home network offer network security to
      protect the devices connected to the home network by performing
      DNS-based content filtering.  The network security service may,
      for example, block access to specific domains to enforce parental
      control, block access to malware sites, etc.

   o  ISPs typically block access to some domains due to a requirement
      imposed by an external entity (e.g., Law Enforcement Agency) by
      performing DNS-based content filtering.

   DNS responses can be filtered by sending a bogus ("forged") A or AAAA
   response, NXDOMAIN error or empty answer, or an extended error code
   defined in [I-D.ietf-dnsop-extended-error].  Each of these have
   advantages and disadvantages, discussed below:

   1.  The DNS response is forged providing IP addresses that point to a
       HTTP(S) server alerting the end user of the reason for blocking
       access to the domain (e.g., malware).  When a HTTP(S) enabled
       domain name is blocked, the network security device presents a
       block page instead of the HTTP response from the content
       provider.  If an HTTP enabled domain name is blocked, the network
       security device intercepts the HTTP request and returns a block
       page over HTTP.  If an HTTPS enabled domain is blocked, the block
       page is also served over HTTPS.  In order to return a block page
       over HTTPS, man in the middle (MITM) is enabled on endpoints by
       generating a local root certificate and an accompanying (local)
       public/private key pair.  The local root certificate is installed
       on the endpoint, and the network security device(s) store a copy
       of the private key.  During the TLS handshake, the network
       security device modifies the certificate provided by the server
       and (re)signs it with the private key from the local root
       certificate.

       *  However, configuring the local root certificate on endpoints
          is not viable option in several deployments like Home
          networks, Schools, Small Office/Home Office (SOHO), and Small/
          Medium Enterprise (SME).  In these cases, the typical behavior
          is that the forged DNS response directs the user towards a
          server hosted to display the block page which breaks the TLS
          connection.  For web-browsing this then results in an HTTPS
          certificate error message indicating that a secure connection
          could not be established, which gives no information to the
          end-user about the reason for the error.  The typical errors
          are "The security certificate presented by this website was
          not issued by a trusted certificate authority" (Internet
          Explorer/Edge"), "The site's security certificate is not
          trusted" (Chrome), "This Connection is Untrusted" (Firefox),




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          "Safari can't verify the identity of the website..." (Safari
          on MacOS)".

       *  Enterprise networks do not assume that all the devices
          connected to their network are managed by the IT team or
          Mobile Device Management (MDM) devices, especially in the
          quite common BYOD ("Bring Your Own Device") scenario.  In
          addition, the local root certificate cannot be installed on
          IoT devices without a device management tool.

       *  An end user does not know why the connection was reset and,
          consequently, may repeatedly try to unsuccessfully reach the
          domain.  Frustrated, the end user may use insecure interfaces
          to reach the domain, potentially compromising both security
          and privacy.  Furthermore, certificate errors train users to
          click through certificate errors, which is poor security
          practice.  To eliminate the need for an end user to click
          through certificate errors, an end user may manually install a
          local root certificate [Chrome-Install-Cert] on a host device.
          Doing so, however, is also poor security practice as it
          creates a security vulnerability that may be exploited by a
          MITM attack.  When the manually installed local root
          certificate expires, the user has to (again) manually install
          the new local root certificate.

   2.  The DNS response is forged to provide a NXDOMAIN response to
       cause the DNS lookup to terminate in failure.  In this case, an
       end user does not know why the domain cannot be reached, and may
       repeatedly try to unsuccessfully reach the domain.  Frustrated,
       the end user may use insecure interfaces to reach the domain,
       potentially compromising both security and privacy.

   3.  The extended error codes Blocked, Censored, and Filtered defined
       in [I-D.ietf-dnsop-extended-error] can be returned by the DNS
       server to provide additional information about the cause of an
       DNS error.  If the extended error code "Forged answer" defined in
       [I-D.ietf-dnsop-extended-error] is returned by the DNS server,
       the client can identify the DNS response is forged and the reason
       for HTTPS certificate error.  These extended error codes do not
       suffer from the limitations discussed in (1) and (2) but the user
       still does not know the exact reason nor the user is aware of the
       exact entity blocking the access to the domain.  For example, a
       DNS server may block access domain based on the content category
       like "Adult Content" to enforce parental control, "Violence &
       Terrorism" due to an external requirement imposed by an external
       entity (e.g., Law Enforcement Agency), etc.  The content
       categories for domains cannot be standardized because the
       classification of domains into content categories is vendor



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       specific, typically ranges from 40 to 100 types of categories
       depending on the vendor and the categories keep evolving.
       Further, the threat data used to categorize domains may sometimes
       mis-classify domains (e.g., Domains wrongly classified as DGA
       (Domain Generation Algorithm) by deep learning techniques, domain
       wrongly classified as phishing due to crowd sourcing, new domains
       not categorized by the threat data).  The end user needs to know
       the contact details of the IT/InfoSec team to raise a complaint.

   No matter which type of response is generated (forged IP address,
   NXDOMAIN or empty answer, or an extended error code), the user who
   generated the query has little chance to understand which entity
   filtered the query, how to report a mistake in the filter, or why the
   entity filtered it at all.  This document describes a mechanism to
   provide a URI which, when accessed, provides such information to the
   user.

   One of the other benefits of this approach is to eliminate the need
   to "spoof" block pages for HTTPS resources, as the block page no
   longer needs to create a signed certificate when blocking a
   destination.  This avoids the need to install a local root
   certificate authority on those IT-managed devices.

2.  Terminology

   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 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document makes use of the terms defined in [RFC8499] and
   [I-D.ietf-dnsop-terminology-ter].

   'Encrypted DNS' refers to DNS-over-HTTPS [RFC8484], DNS-over-TLS
   [RFC7858], or DNS-over-QUIC [I-D.ietf-dprive-dnsoquic].

3.  Error page URI EDNS0 option format

   This document uses an EDNS0 [RFC6891] option to include the URI that
   gives additional information in a DNS response about the cause of
   blocking access to a domain.  The option is structured as follows:









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                                                1   1   1   1   1   1
        0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |                            OPTION-CODE                        |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |                           OPTION-LENGTH                       |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |                 ERROR-PAGE-URI-LENGTH  (fixed size)           |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      /                    ERROR-PAGE-URI (variable size)             /
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |                    ERROR-PAGE-SIG-ALG (fixed size)            |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      /                     ERROR-PAGE-SIG  (variable size)           /
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

   The description of the fields is as follows:

   o  OPTION-CODE: TBD, indicates the code assigned for Error page URI
      (Section 6.1.2 of [RFC6891]).  [RFC Editor: change TBD to the
      proper code once assigned by IANA.]

   o  OPTION-LENGTH: See Section 6.1.2 of [RFC6891].  This fields
      contains the length of the payload (everything after OPTION-
      LENGTH) in octets.  The variability of the option length stems
      from the variable-length ERROR-PAGE-URI and ERROR-PAGE-SIG fields.

   o  ERROR-PAGE-URI-LENGTH: This 16-bit field indicates the length of
      ERROR-PAGE-URI.  It MUST NOT be set to 0.

   o  ERROR-PAGE-URI: a variable length UTF-8 encoded [RFC5198] text
      field containing the URI Template [RFC6570] that gives additional
      information about the cause of blocking access to a domain.  The
      ERROR-PAGE-URI field MUST NOT be zero octets in length.

   o  ERROR-PAGE-SIG-ALG: A 16-bits field that contains the algorithm
      used to generate the signature for the Error page URI Template.
      The values are defined in the TLS SignatureScheme [TLS-SIG-SCHEME]
      with limitations described in Section 5.

   o  ERROR-PAGE-SIG, a variable length field containing the signature
      of the Error page URI Template.  The signature generation process
      is discussed in Section 5.

   The Error page URI option can be included in any response (SERVFAIL,
   NXDOMAIN, REFUSED, and even NOERROR, etc) to a query that includes
   OPT Pseudo-RR [RFC6891].




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   The URI Template defined in ERROR-PAGE-URI describes how to construct
   the URL to fetch the error page.  The agent acting as HTTPS client on
   the endpoint encodes a FQDN to which access is denied into an HTTP
   GET request to retrieve the error page.  The HTTPS server returning
   the error page defines the URI used by the HTTP GET request through
   the use of a URI Template.  The URI Template is processed with a
   defined variable "target-domain" whose value is set to the FQDN to
   which access is denied.  The FQDN is encoded using base64url
   [RFC4648] and then provided as the variable value for "target-domain"
   to expand the URI Template into a URI reference in the HTTP GET
   request.  Padding characters for base64url MUST NOT be included.

   An example is illustrated below:

   If the URI Template is "https://block.example.net/block-page{?target-
   domain}" for the HTTPS server returning the error page and access to
   the target domain "example.com" is blocked by the encrypted DNS
   server, the variable "target-domain" has the value "example.com"
   base64url encoded into an HTTP GET request.  In the above example,
   the expansion of the above URI Template is
   "https://block.example.net/block-page?target-domain=ZXhhbXBsZS5jb20".

   HTTP/2 [RFC7540] is the minimum RECOMMENDED version of HTTP to use to
   retrieve the error page.  The HTTPS client retrieving the error page
   MUST verify the entire certification path per [RFC5280].  The HTTPS
   client additionally uses validation techniques as described in
   [RFC6125] to compare the domain name in the error page URI to the
   server certificate provided in TLS handshake.  See [RFC7525] for
   additional TLS recommendations.

4.  Error page URI Processing

   The DNS client MUST follow the following rules to process the Error
   page URI EDNS0 option:

   o  The Error page URI EDNS0 option is susceptible to forgery.  In
      order to defend against this attack the DNS client MUST NOT
      process the DNS response with Error page URI EDNS0 option unless
      DNS messages exchanged are cryptographically protected using
      encrypted DNS.

   o  If an DNS client has enabled opportunistic privacy profile
      (Section 5 of [RFC8310]) for DoT, the DNS client will either
      fallback to an encrypted connection without authenticating the DNS
      server provided by the local network or fallback to clear text
      DNS, and cannot exchange encrypted DNS messages.  The fallback
      adversely impacts security and privacy.  If the DNS client has




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      enabled opportunistic privacy profile for DoT, the client MUST NOT
      process the DNS response with Error page URI EDNS0 option.

   o  If an DNS client has enabled strict privacy profile (Section 5 of
      [RFC8310]) for DoT, the DNS client requires an encrypted
      connection and successful authentication of the DNS server; this
      mitigates both passive eavesdropping and client redirection (at
      the expense of providing no DNS service if an encrypted,
      authenticated connection is not available).  If the DNS client has
      enabled strict privacy profile for DoT, the client can process the
      DNS response with Error page URI EDNS0 option.  Note that the
      strict and opportunistic privacy profiles as defined in [RFC8310]
      only applies to DoT protocol, there has been no such distinction
      made for DoH protocol.

   o  If the DNS response contains more than one Error page URI EDNS0
      option, the DNS client MUST discard all Error page URI EDNS0
      options in the DNS response.

   o  The Error page URI EDNS0 option MUST be processed by the DNS
      client for a "Censored", "Blocked", "Filtered" or "Forged"
      extended error codes and MUST be ignored for any other type of
      extended DNS error code.  When "Censored", "Blocked", "Filtered"
      or "Forged" extended error code is returned in conjunction with an
      Error page URI EDNS0 option, any other resource records in the
      answer MUST be ignored by clients supporting this specification.

   o  If the DNS client determines that the encrypted DNS server does
      not offer DNS filtering service, it MUST reject the Error page URI
      EDNS0 option.  For example, the DNS client knows whether the pre-
      configured encrypted DNS resolver performs DNS-based content
      filtering or not.

   o  The DNS client MUST reject the error page URI if the scheme is not
      "https".

   o  The DNS client verifies the signature in the ERROR-PAGE-SIG field
      following the mechanism discussed in Section 5.  If the signature
      is valid, the client can positively identify that the Error page
      URI EDNS0 option has been generated by the encrypted DNS server
      and the encrypted DNS server did not forward the Error Page URI
      EDNS0 option from an upstream resolver.  If signature validation
      fails, the DNS client MUST reject the Error page URI EDNS0 option.

   Because EDNS is a hop-by-hop extension to DNS and EDNS responses are
   not cached (Section 6.2.1 of [RFC6891]), a DNS resolver MUST NOT
   propagate a received Error Page URI EDNS0 option, because an attacker
   could insert a bogus URI; instead, if access to a domain is denied,



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   the DNS resolver MUST generate its own Error Page URI.  Because DNS
   forwarders (or DNS proxies) are supposed to propagate unknown EDNS0
   options (Section 4.1 and Section 4.4.1 of [RFC5625]), the Error Page
   URI EDNS0 option may get propagated.  To detect both of these
   scenarios, the Error Page URI Template is protected with an object
   signature as described in Section 5.

5.  Sign and Verify

   The algorithms for generating signature for DNS resource record sets
   (RRsets) are defined in [DNSKEY-IANA].  The "mandatory-to-implement"
   algorithms are RSA, Elliptic Curve Digital Signature Algorithm
   (ECDSA), and Edwards-curve Digital Security Algorithm (EdDSA)
   [RFC8624].  Along similar lines, the encrypted DNS server's end-
   entity certificate's public key and the signature algorithm with
   which the key can be used are RSA, ECDSA, and EdDSA [RFC8446].  If
   ECDSA is used, it is RECOMMENDED to use the deterministic digital
   signature generation procedure of the ECDSA, specified in [RFC6979].

   The signature is generated by the encrypted DNS server using the
   Error page URI Template, private key of the encrypted DNS server's
   end-entity certificate as inputs to the signature algorithm.  The
   signature algorithm in the ERROR-PAGE-SIG-ALG field MUST be
   compatible with the key in the DNS server's end-entity certificate.
   The implementation MUST support the same set of algorithms in the TLS
   client for validating the signature in the CertificateVerify message
   from the server in the TLS handshake and in the DNS client to
   validate the signature for the Error page URI Template.  As a
   reminder, the server's end-entity certificate's public key will be
   compatible with the selected authentication algorithm from the
   client's "signature_algorithms" TLS extension (Section 4.4.2.2 of
   [RFC8624]).

   If the signature algorithm in the ERROR-PAGE-SIG-ALG field is not
   compatible with the key in the DNS server's end-entity certificate,
   the DNS client MUST reject the Error page URI EDNS0 option.  The DNS
   client verifies the signature using the signature in the ERROR-PAGE-
   SIG field, error page URI Template and DNS server's end-entity
   certificate's public key as inputs to the signature algorithm.  For
   example, if Ed25519 is used, Ed25519 signature algorithm and
   verification of the Ed25519 signature are described in Sections 5.1.6
   and 5.1.7 of [RFC8032], respectively.

6.  ERROR Page

   The following text outlines the RECOMMENDED contents of an error page
   to assist the operator developing the error page.




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   o  The exact reason for blocking access to the domain.  If the domain
      is blocked based on some threat data, the threat type associated
      with the blocked domain can be provided/displayed to the end user.
      For example, the reason can indicate the type of malware blocked
      like spyware and the damage it can do the security and privacy of
      the user.

   o  The domain name blocked.

   o  If query was blocked by regulation, a pointer to a regulatory text
      that mandates this query block.

   o  The entity (or organization) blocking the access to the domain and
      contact details of the IT/InfoSec team to raise a complaint.

   o  The blocked error page to not include Ads and dynamic content.

   The content of the error page discussed above is non-normative, the
   above text only provides the guidelines and template for the error
   page and.

   o  Does not attempt to offer an exhaustive list for the contents of
      an error page.

   o  It is not intended to form the basis of any legal/compliance for
      developing the error page.

7.  Usability Considerations

   The error page SHOULD be returned in the user's preferred language as
   expressed by the Accept-Language header.  If the error page is
   displayed in a language not known to the end user and assuming
   Internationalization features failed, browser extensions to translate
   to user's native language can be used.  For example, "Google
   Translate" extension [Chrome-Translate] provided by Google on Chrome
   can be used by the user to translate the error page.  The "Google
   Translate" extension automatically detects whether the language of a
   page is different from the language the user has selected.  If it is
   in a different language, a banner appears at the top of the page.
   The user can click on the Translate button in the banner to have all
   the text on the page appear in the language selected by the user.

8.  Security Considerations

   Security considerations in [I-D.ietf-dnsop-extended-error] and
   [RFC8624] need to be taken into consideration.





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   The Error page URI EDNS0 option causes an HTTPS retrieval by the
   client.  To prevent forgery of the Error page URI EDNS0 option, this
   specification requires it only be sent only over an encrypted DNS
   channel with an authorized DNS server.

   The client knows it is connecting to a HTTPS server returning the
   error page.  To reduce threat surface the client can retrieve the
   Error page URL using, for example, an isolated environment and take
   other precautions such as clearly labeling the page as untrusted or
   prevent user interaction with the page.  Such isolation should
   prevent transmitting cookies, block JavaScript, block auto-fill of
   credentials or personal information, and be isolated from the user's
   normal environment.

   Browsers perform some of the above restrictions when accessing
   captive portals (Section 5 of [RFC8910] or [Safari-Cookie]), during
   private browsing, or using containerization [Facebook-Container].

   Note that the means to use a sandbox environment and a user interface
   presenting the error page are not covered in this document.  By its
   nature, these aspects are implementation specific and best left to
   the application and user interface designers.

   The encrypted DNS session provides transport security for the
   interaction between the DNS client and server, but DNSSEC signing and
   validation is not possible for the Error Page URI EDNS0 option
   returning the error page URI template.  For example, if access to a
   doman is blocked, the encrypted DNS resolver can rewrite the response
   to send NXDOMAIN error and Error page URI EDNS0 option in the DNS
   response, it will omit DNSSEC RRsets, because the modified responses
   cannot be verified by DNSSEC signatures.  However, the signature in
   the Error Page URI EDNS0 option provides data origin authentication
   of the Error Page URI EDNS0 option.  Nevertheless, the Error Page URI
   EDNS0 option returning the error page URI Template should be treated
   only as diagnostic information and MUST NOT alter DNS protocol
   processing.

   By design, the object referenced by the error page URL potentially
   exposes additional information about the DNS resolution process that
   may leak information.  An example of this is the reason for blocking
   the access to the domain name and the entity blocking access to the
   domain.

9.  IANA Considerations







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9.1.  A New Error Page URI EDNS Option

   This document defines a new EDNS(0) option, entitled "Error Page
   URI", assigned a value of TBD from the "DNS EDNS0 Option Codes (OPT)"
   registry [to be removed upon publication:
   [http://www.iana.org/assignments/dns-parameters/dns-
   parameters.xhtml#dns-parameters-11]

   Value  Name                 Status    Reference
   -----  ----------------     ------    ------------------
    TBD   Error Page URI      Standard       [ This document ]

10.  Acknowledgements

   Thanks to Vittorio Bertola, Wes Hardaker, Ben Schwartz, Erid Orth,
   Viktor Dukhovni, Warren Kumari and Bob Harold for the comments.

11.  References

11.1.  Normative References

   [I-D.ietf-dnsop-extended-error]
              Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", draft-ietf-dnsop-
              extended-error-16 (work in progress), May 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <https://www.rfc-editor.org/info/rfc5198>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",
              BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
              <https://www.rfc-editor.org/info/rfc5625>.



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   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <https://www.rfc-editor.org/info/rfc6570>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [RFC6979]  Pornin, T., "Deterministic Usage of the Digital Signature
              Algorithm (DSA) and Elliptic Curve Digital Signature
              Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
              2013, <https://www.rfc-editor.org/info/rfc6979>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/info/rfc8310>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.






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   [RFC8624]  Wouters, P. and O. Sury, "Algorithm Implementation
              Requirements and Usage Guidance for DNSSEC", RFC 8624,
              DOI 10.17487/RFC8624, June 2019,
              <https://www.rfc-editor.org/info/rfc8624>.

   [TLS-SIG-SCHEME]
              "IANA, TLS SignatureScheme",
              <https://www.iana.org/assignments/tls-parameters/tls-
              parameters.xhtml#tls-signaturescheme>.

11.2.  Informative References

   [Chrome-Install-Cert]
              "How to manually install the Securly SSL certificate in
              Chrome", <support.securly.com/hc/en-us/articles/206081828-
              How-to-manually-install-the-Securly-SSL-certificate-in-
              Chrome>.

   [Chrome-Translate]
              "Google Translate",
              <https://chrome.google.com/webstore/detail/google-
              translate/aapbdbdomjkkjkaonfhkkikfgjllcleb/RK%3D2/
              RS%3DBBFW_pnWkPY0xPMYsAZI5xOgQEE->.

   [DNSKEY-IANA]
              "IANA, Domain Name System Security (DNSSEC) Algorithm
              Numbers",
              <http://www.iana.org/assignments/dns-sec-alg-numbers>.

   [Facebook-Container]
              "Facebook container for Firefox",
              <https://www.mozilla.org/en-US/firefox/
              facebookcontainer/>.

   [I-D.ietf-dnsop-terminology-ter]
              Hoffman, P., "Terminology for DNS Transports and
              Location", draft-ietf-dnsop-terminology-ter-02 (work in
              progress), August 2020.

   [I-D.ietf-dprive-dnsoquic]
              Huitema, C., Mankin, A., and S. Dickinson, "Specification
              of DNS over Dedicated QUIC Connections", draft-ietf-
              dprive-dnsoquic-00 (work in progress), April 2020.

   [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>.



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   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

   [RFC8910]  Kumari, W. and E. Kline, "Captive-Portal Identification in
              DHCP and Router Advertisements (RAs)", RFC 8910,
              DOI 10.17487/RFC8910, September 2020,
              <https://www.rfc-editor.org/info/rfc8910>.

   [Safari-Cookie]
              "Isolated cookie store (CVE-2016-1730)",
              <https://support.apple.com/en-us/HT205732>.

Authors' Addresses

   Tirumaleswar Reddy
   McAfee, Inc.
   Embassy Golf Link Business Park
   Bangalore, Karnataka  560071
   India

   Email: kondtir@gmail.com


   Neil Cook
   Open-Xchange
   UK

   Email: neil.cook@noware.co.uk


   Dan Wing
   Citrix Systems, Inc.
   USA

   Email: dwing-ietf@fuggles.com






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   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com













































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