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dprive                                                      S. Dickinson
Internet-Draft                                                   Sinodun
Updates: 7858 (if approved)                                   D. Gillmor
Intended status: Standards Track                                    ACLU
Expires: December 18, 2017                                      T. Reddy
                                                                  McAfee
                                                           June 16, 2017


             Usage and (D)TLS Profiles for DNS-over-(D)TLS
               draft-ietf-dprive-dtls-and-tls-profiles-10

Abstract

   This document discusses Usage Profiles, based on one or more
   authentication mechanisms, which can be used for DNS over Transport
   Layer Security (TLS) or Datagram TLS (DTLS).  These profiles can
   increase the privacy of DNS transactions compared to using only clear
   text DNS.  This document also specifies new authentication mechanisms
   - it describes several ways a DNS client can use an authentication
   domain name to authenticate a (D)TLS connection to a DNS server.
   Additionally, it defines (D)TLS protocol profiles for DNS clients and
   servers implementing DNS-over-(D)TLS.  This document updates RFC
   7858.

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 http://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 December 18, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Usage Profiles  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  DNS Resolution  . . . . . . . . . . . . . . . . . . . . .  10
   6.  Authentication in DNS-over(D)TLS  . . . . . . . . . . . . . .  10
     6.1.  DNS-over-(D)TLS Startup Configuration Problems  . . . . .  10
     6.2.  Credential Verification . . . . . . . . . . . . . . . . .  11
     6.3.  Summary of Authentication Mechanisms  . . . . . . . . . .  11
     6.4.  Combining Authentication Mechanisms . . . . . . . . . . .  14
     6.5.  Authentication in Opportunistic Privacy . . . . . . . . .  14
     6.6.  Authentication in Strict Privacy  . . . . . . . . . . . .  15
     6.7.  Implementation guidance . . . . . . . . . . . . . . . . .  15
   7.  Sources of Authentication Domain Names  . . . . . . . . . . .  15
     7.1.  Full direct configuration . . . . . . . . . . . . . . . .  15
     7.2.  Direct configuration of ADN only  . . . . . . . . . . . .  16
     7.3.  Dynamic discovery of ADN  . . . . . . . . . . . . . . . .  16
       7.3.1.  DHCP  . . . . . . . . . . . . . . . . . . . . . . . .  16
   8.  Authentication Domain Name based Credential Verification  . .  17
     8.1.  PKIX Certificate Based Authentication . . . . . . . . . .  17
     8.2.  DANE  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
       8.2.1.  Direct DNS Lookup . . . . . . . . . . . . . . . . . .  18
       8.2.2.  TLS DNSSEC Chain extension  . . . . . . . . . . . . .  18
   9.  (D)TLS Protocol Profile . . . . . . . . . . . . . . . . . . .  19
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  20
     11.1.  Counter-measures to DNS Traffic Analysis . . . . . . . .  20
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  21
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     13.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Server capability probing and caching by DNS clients  24
   Appendix B.  Changes between revisions  . . . . . . . . . . . . .  24
     B.1.  -10 version . . . . . . . . . . . . . . . . . . . . . . .  25
     B.2.  -09 version . . . . . . . . . . . . . . . . . . . . . . .  26



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     B.3.  -08 version . . . . . . . . . . . . . . . . . . . . . . .  26
     B.4.  -07 version . . . . . . . . . . . . . . . . . . . . . . .  26
     B.5.  -06 version . . . . . . . . . . . . . . . . . . . . . . .  26
     B.6.  -05 version . . . . . . . . . . . . . . . . . . . . . . .  27
     B.7.  -04 version . . . . . . . . . . . . . . . . . . . . . . .  27
     B.8.  -03 version . . . . . . . . . . . . . . . . . . . . . . .  27
     B.9.  -02 version . . . . . . . . . . . . . . . . . . . . . . .  27
     B.10. -01 version . . . . . . . . . . . . . . . . . . . . . . .  28
     B.11. draft-ietf-dprive-dtls-and-tls-profiles-00  . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction

   DNS Privacy issues are discussed in [RFC7626].  The specific issues
   described there that are most relevant to this document are

   o  Passive attacks which eavesdrop on clear text DNS transactions on
      the wire (Section 2.4) and

   o  Active attacks which redirect clients to rogue servers to monitor
      DNS traffic (Section 2.5.3).

   Mitigating against these attacks increases the privacy of DNS
   transactions, however many of the other issues raised in [RFC7626]
   still apply.

   Two documents that provide ways to increase DNS privacy between DNS
   clients and DNS servers are:

   o  Specification for DNS over Transport Layer Security (TLS)
      [RFC7858], referred to here as simply 'DNS-over-TLS'

   o  DNS over Datagram Transport Layer Security (DTLS) [RFC8094],
      referred to here simply as 'DNS-over-DTLS'.  Note that this
      document has the Category of Experimental.

   Both documents are limited in scope to communications between stub
   clients and recursive resolvers and the same scope is applied to this
   document (see Section 2 and Section 3).  The proposals here might be
   adapted or extended in future to be used for recursive clients and
   authoritative servers, but this application was out of scope for the
   Working Group charter at the time this document was finished.

   This document specifies two Usage Profiles (Strict and Opportunistic)
   for DTLS [RFC6347] and TLS [RFC5246] which provide improved levels of
   mitigation against the attacks described above compared to using only
   clear text DNS.




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   Section 5 presents a generalized discussion of Usage Profiles by
   separating the Usage Profile, which is based purely on the security
   properties it offers the user, from the specific mechanism(s) that
   are used for DNS server authentication.  The Profiles described are:

   o  A Strict Profile that requires an encrypted connection and
      successful authentication of the DNS server which mitigates both
      passive eavesdropping and client re-direction (at the expense of
      providing no DNS service if this is not available).

   o  An Opportunistic Profile that will attempt, but does not require,
      encryption and successful authentication; it therefore provides
      limited or no mitigation against such attacks but offers maximum
      chance of DNS service.

   The above Usage Profiles attempt authentication of the server using
   at least one authentication mechanism.  Section 6.4 discusses how to
   combine authentication mechanisms to determine the overall
   authentication result.  Depending on that overall authentication
   result (and whether encryption is available) the Usage Profile will
   determine if the connection should proceed, fallback or fail.

   One authentication mechanism is already described in [RFC7858].  That
   document specifies a Subject Public Key Info (SPKI) based
   authentication mechanism for DNS-over-TLS in the context of a
   specific case of a Strict Usage Profile using that single
   authentication mechanism.  Therefore the "Out-of-band Key-pinned
   Privacy Profile" described in [RFC7858] would qualify as a "Strict
   Usage Profile" that used SPKI pinning for authentication.

   This document extends the use of SPKI pinset based authentication so
   that it is considered a general authentication mechanism that can be
   used with either DNS-over-(D)TLS Usage Profile.  That is, the SPKI
   pinset mechanism described in [RFC7858] MAY be used with DNS-
   over-(D)TLS.

   This document also describes a number of additional authentication
   mechanisms all of which specify how a DNS client should authenticate
   a DNS server based on an 'authentication domain name'.  In
   particular, the following is described:

   o  How a DNS client can obtain the combination of an authentication
      domain name and IP address for a DNS server.  See Section 7.

   o  What are the acceptable credentials a DNS server can present to
      prove its identity for (D)TLS authentication based on a given
      authentication domain name.  See Section 8.




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   o  How a DNS client can verify that any given credential matches the
      authentication domain name obtained for a DNS server.  See
      Section 8.

   In Section 9 this document defines a (D)TLS protocol profile for use
   with DNS.  This profile defines the configuration options and
   protocol extensions required of both parties to optimize connection
   establishment and session resumption for transporting DNS, and to
   support all currently specified authentication mechanisms.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Several terms are used specifically in the context of this draft:

   o  DNS client: a DNS stub resolver or forwarder.  In the case of a
      forwarder, the term "DNS client" is used to discuss the side that
      sends queries.

   o  DNS server: a DNS recursive resolver or forwarder.  In the case of
      a forwarder, the term "DNS server" is used to discuss the side
      that responds to queries.  For emphasis, in this document the term
      does not apply to authoritative servers.

   o  Privacy-enabling DNS server: A DNS server that implements DNS-
      over-TLS [RFC7858] and may optionally implement DNS-over-DTLS
      [RFC8094].  The server should also offer at least one of the
      credentials described in Section 8 and implement the (D)TLS
      profile described in Section 9.

   o  (D)TLS: For brevity this term is used for statements that apply to
      both Transport Layer Security [RFC5246] and Datagram Transport
      Layer Security [RFC6347].  Specific terms will be used for any
      statement that applies to either protocol alone.

   o  DNS-over-(D)TLS: For brevity this term is used for statements that
      apply to both DNS-over-TLS [RFC7858] and DNS-over-DTLS [RFC8094].
      Specific terms will be used for any statement that applies to
      either protocol alone.

   o  Authentication domain name: A domain name that can be used to
      authenticate a privacy-enabling DNS server.  Sources of
      authentication domain names are discussed in Section 7.





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   o  SPKI Pinsets: [RFC7858] describes the use of cryptographic digests
      to "pin" public key information in a manner similar to HTTP Public
      Key Pinning [RFC7469] (HPKP).  An SPKI pinset is a collection of
      these pins that constrains a DNS server.

   o  Authentication information: Information a DNS client may use as
      the basis of an authentication mechanism.  In this context that
      can be either a:

      *  a SPKI pinset or

      *  an authentication domain name

   o  Reference Identifier: a Reference Identifier as described in
      [RFC6125], constructed by the DNS client when performing TLS
      authentication of a DNS server.

   o  Credential: Information available for a DNS server which proves
      its identity for authentication purposes.  Credentials discussed
      here include:

      *  PKIX certificate

      *  DNSSEC validated chain to a TLSA record

      but may also include SPKI pinsets.

3.  Scope

   This document is limited to describing

   o  Usage Profiles based on general authentication mechanisms

   o  The details of domain name based authentication of DNS servers by
      DNS clients (as defined in the terminology section)

   o  The (D)TLS profiles needed to support authentication in DNS-
      over-(D)TLS.

   As such, the following things are out of scope:

   o  Authentication of authoritative servers by recursive resolvers.

   o  Authentication of DNS clients by DNS servers.

   o  The details of how to perform SPKI-pinset-based authentication.
      This is defined in [RFC7858].




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   o  Any server identifier other than domain names, including IP
      addresses, organizational names, country of origin, etc.

4.  Discussion

   One way to mitigate against passive attackers eavesdropping on clear
   text DNS transactions is to encrypt the query (and response).  Such
   encryption typically provides integrity protection as a side-effect,
   which means on-path attackers cannot simply inject bogus DNS
   responses.  To also mitigate against active attackers pretending to
   be the server, the client must authenticate the (D)TLS connection to
   the server.

   This document discusses Usage Profiles, which provide differing
   levels of attack mitigation to DNS clients, based on the requirements
   for authentication and encryption, regardless of the context (for
   example, which network the client is connected to).  A Usage Profile
   is a distinct concept to a usage policy or usage model, which might
   dictate which Profile should be used in a particular context
   (enterprise vs coffee shop), with a particular set of DNS Servers or
   with reference to other external factors.  A description of the
   variety of usage policies is out of scope of this document, but may
   be the subject of future work.

   The term 'privacy-enabling DNS server' is used throughout this
   document.  This is a DNS server that:

   o  MUST implement DNS-over-TLS [RFC7858].

   o  MAY implement DNS-over-DTLS [RFC8094].

   o  SHOULD offer at least one of the credentials described in
      Section 8.

   o  Implements the (D)TLS profile described in Section 9.

5.  Usage Profiles

   A DNS client has a choice of Usage Profiles available to increase the
   privacy of DNS transactions.  This choice is briefly discussed in
   both [RFC7858] and [RFC8094].  These Usage Profiles are:

   o  Strict profile: the DNS client requires both an encrypted and
      authenticated connection to a privacy-enabling DNS Server.  A hard
      failure occurs if this is not available.  This requires the client
      to securely obtain authentication information it can use to
      authenticate the server.  This profile mitigates against both
      passive and active attacks providing the client with the best



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      available privacy for DNS.  This Profile is discussed in detail in
      Section 6.6.

   o  Opportunistic Privacy: the DNS client uses Opportunistic Security
      as described in [RFC7435]

         "... the use of cleartext as the baseline communication
         security policy, with encryption and authentication negotiated
         and applied to the communication when available."

      The use of Opportunistic Privacy is intended to support
      incremental deployment of increased privacy with a view to
      widespread adoption of the Strict profile.  It should be employed
      when the DNS client might otherwise settle for cleartext; it
      provides the maximum protection an attacker will allow.  As
      described in [RFC7435] it might result in

      *  an encrypted and authenticated connection

      *  an encrypted connection

      *  a clear text connection

      depending on the fallback logic of the client, the available
      authentication information and the capabilities of the DNS Server.
      In all these cases the DNS client is willing to continue with a
      connection to the DNS Server and perform resolution of queries.

   Both profiles can include an initial meta query (performed using an
   Opportunistic lookup) to obtain the IP address for the privacy-
   enabling DNS server to which the DNS client will subsequently
   connect.  The rationale for permitting this for the Strict profile is
   that requiring such meta queries to also be performed using the
   Strict profile would introduce significant deployment obstacles.
   However, it should be noted that in this scenario an active attack is
   possible on the meta query which could result in the client not being
   able to connect to a privacy-enabling DNS server that it can
   authenticate.

   To compare the two Usage profiles the table below shows a successful
   Strict profile along side the 3 possible outcomes of an Opportunistic
   profile.  In the best case scenario for the Opportunistic profile (an
   authenticated and encrypted connection) it is equivalent to the
   Strict profile.  In the worst case scenario it is equivalent to clear
   text.  Clients using the Opportunistic profile SHOULD try for the
   best case but MAY fallback to the intermediate case and eventually
   the worst case scenario in order to obtain a response.  One reason to
   fallback without trying every available privacy-enabling DNS server



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   is if latency is more important than attack mitigation, see
   Appendix A.  The Opportunistic profile therefore provides varying
   protection depending on what kind of connection is actually used
   including no attack mitigation at all.

   Note that there is no requirement in Opportunistic Security to notify
   the user what type of connection is actually used, the 'detection'
   described below is only possible if such connection information is
   available.  However, if it is available and the user is informed that
   an unencrypted connection was used to connect to a server then the
   user should assume (detect) that the connection is subject to both
   active and passive attack since the DNS queries are sent in clear
   text.  This might be particularly useful if a new connection to a
   certain server is unencrypted when all previous connections were
   encrypted.  Similarly if the user is informed that an encrypted but
   unauthenticated connection was used then the user can detect that the
   connection may be subject to active attack.  In other words for the
   cases where no protection is provided against an attacker (N) it is
   possible to detect that an attack might be happening (D).  This is
   discussed in Section 6.5.

    +---------------+------------+------------------+-----------------+
    | Usage Profile | Connection | Passive Attacker | Active Attacker |
    +---------------+------------+------------------+-----------------+
    |     Strict    |    A, E    |        P         |        P        |
    | Opportunistic |    A, E    |        P         |        P        |
    | Opportunistic |     E      |        P         |       N, D      |
    | Opportunistic |            |       N, D       |       N, D      |
    +---------------+------------+------------------+-----------------+

   P == Protection; N == No protection; D == Detection is possible; A ==
            Authenticated connection; E == Encrypted connection

     Table 1: Attack protection by Usage Profile and type of attacker

   The Strict profile provides the best attack mitigation and therefore
   SHOULD always be implemented in DNS clients that implement
   Opportunistic Privacy.

   A DNS client that implements DNS-over-(D)TLS SHOULD NOT be configured
   by default to use only clear text.

   The choice between the two profiles depends on a number of factors
   including which is more important to the particular client:

   o  DNS service at the cost of no attack mitigation (Opportunistic) or





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   o  best available attack mitigation at the potential cost of no DNS
      service (Strict).

   Additionally the two profiles require varying levels of configuration
   (or a trusted relationship with a provider) and DNS server
   capabilities, therefore DNS clients will need to carefully select
   which profile to use based on their communication needs.

   A DNS server that implements DNS-over-(D)TLS SHOULD provide at least
   one credential so that those DNS clients that wish to do so are able
   to use the Strict profile (see Section 2).

5.1.  DNS Resolution

   A DNS client SHOULD select a particular Usage Profile when resolving
   a query.  A DNS client MUST NOT fallback from Strict Privacy to
   Opportunistic Privacy during the resolution of a given query as this
   could invalidate the protection offered against attackers.  It is
   anticipated that DNS clients will use a particular Usage Profile for
   all queries to all configured servers until an operational issue or
   policy update dictates a change in the profile used.

6.  Authentication in DNS-over(D)TLS

   This section describes authentication mechanisms and how they can be
   used in either Strict or Opportunistic Privacy for DNS-over-(D)TLS.

6.1.  DNS-over-(D)TLS Startup Configuration Problems

   Many (D)TLS clients use PKIX authentication [RFC6125] based on an
   authentication domain name for the server they are contacting.  These
   clients typically first look up the server's network address in the
   DNS before making this connection.  Such a DNS client therefore has a
   bootstrap problem, as it will typically only know the IP address of
   its DNS server.

   In this case, before connecting to a DNS server, a DNS client needs
   to learn the authentication domain name it should associate with the
   IP address of a DNS server for authentication purposes.  Sources of
   authentication domain names are discussed in Section 7.

   One advantage of this domain name based approach is that it
   encourages association of stable, human recognizable identifiers with
   secure DNS service providers.







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6.2.  Credential Verification

   The use of SPKI pinset verification is discussed in [RFC7858].

   In terms of domain name based verification, once an authentication
   domain name is known for a DNS server a choice of authentication
   mechanisms can be used for credential verification.  Section 8
   discusses these mechanisms in detail, namely PKIX certificate based
   authentication and DANE.

   Note that the use of DANE adds requirements on the ability of the
   client to get validated DNSSEC results.  This is discussed in more
   detail in Section 8.2.

6.3.  Summary of Authentication Mechanisms

   This section provides an overview of the various authentication
   mechanisms.  The table below indicates how the DNS client obtains
   information to use for authentication for each option; either
   statically via direct configuration or dynamically.  Of course, the
   Opportunistic Usage Profile does not require authentication and so a
   client using that profile may choose to connect to a privacy-enabling
   DNS server on the basis of just an IP address.




























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   +---+------------+-------------+------------------------------------+
   | # | Static     | Dynamically | Short name: Description            |
   |   | Config     | Obtained    |                                    |
   +---+------------+-------------+------------------------------------+
   | 1 | SPKI + IP  |             | SPKI: SPKI pinset(s) and IP        |
   |   |            |             | address obtained out of band       |
   |   |            |             | [RFC7858]                          |
   |   |            |             |                                    |
   | 2 | ADN + IP   |             | ADN: ADN and IP address obtained   |
   |   |            |             | out of band (see Section 7.1)      |
   |   |            |             |                                    |
   | 3 | ADN        | IP          | ADN only: Opportunistic lookups to |
   |   |            |             | a NP DNS server for A/AAAA (see    |
   |   |            |             | Section 7.2)                       |
   |   |            |             |                                    |
   | 4 |            | ADN + IP    | DHCP: DHCP configuration only (see |
   |   |            |             | Section 7.3.1)                     |
   |   |            |             |                                    |
   | 5 | [ADN + IP] | [ADN + IP]  | DANE: DNSSEC chain obtained via    |
   |   |            | TLSA record | Opportunistic lookups to NP DNS    |
   |   |            |             | server (see Section 8.2.1)         |
   |   |            |             |                                    |
   | 6 | [ADN + IP] | [ADN + IP]  | TLS extension: DNSSEC chain        |
   |   |            | TLSA record | provided by PE DNS server in TLS   |
   |   |            |             | DNSSEC chain extension (see        |
   |   |            |             | Section 8.2.2)                     |
   +---+------------+-------------+------------------------------------+

      SPKI == SPKI pinset(s), IP == IP Address, ADN == Authentication
    Domain Name, NP == Network provided, PE == Privacy-enabling, [ ] ==
           Data may be obtained either statically or dynamically

              Table 2: Overview of Authentication Mechanisms

   The following summary attempts to present some key attributes of each
   of the mechanisms (using the 'Short name' from Table 2), indicating
   attractive attributes with a '+' and undesirable attributes with a
   '-'.

   1.  SPKI

          + Minimal leakage (Note that the ADN is always leaked in the
          Server Name Indication (SNI) field in the Client Hello in TLS
          when communicating with a privacy-enabling DNS server)

          - Overhead of on-going key management required

   2.  ADN



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          + Minimal leakage

          + One-off direct configuration only

   3.  ADN only

          + Minimal one-off direct configuration, only a human
          recognizable domain name needed

          - A/AAAA meta queries leaked to network provided DNS server
          that may be subject to active attack

   4.  DHCP

          + No static config

          - Requires a non-standard or future DHCP option in order to
          provide the ADN

          - Requires secure and trustworthy connection to DHCP server if
          used with a Strict Usage profile

   5.  DANE

          The ADN and/or IP may be obtained statically or dynamically
          and the relevant attributes of that method apply

          + DANE options (e.g., matching on entire certificate)

          - Requires a DNSSEC validating stub implementation (deployment
          of which is limited at the time of writing)

          - DNSSEC chain meta queries leaked to network provided DNS
          server that may be subject to active attack

   6.  TLS extension

          The ADN and/or IP may be obtained statically or dynamically
          and the relevant attributes of that method apply

          + Reduced latency compared with 'DANE'

          + No network provided DNS server required if ADN and IP
          statically configured

          + DANE options (e.g., matching on entire certificate)

          - Requires a DNSSEC validating stub implementation



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6.4.  Combining Authentication Mechanisms

   This draft does not make explicit recommendations about how an SPKI
   pinset based authentication mechanism should be combined with a
   domain based mechanism from an operator perspective.  However it can
   be envisaged that a DNS server operator may wish to make both an SPKI
   pinset and an authentication domain name available to allow clients
   to choose which mechanism to use.  Therefore, the following is
   guidance on how clients ought to behave if they choose to configure
   both, as is possible in HPKP [RFC7469].

   A DNS client that is configured with both an authentication domain
   name and a SPKI pinset for a DNS server SHOULD match on both a valid
   credential for the authentication domain name and a valid SPKI pinset
   (if both are available) when connecting to that DNS server.  In this
   case the client SHOULD treat the SPKI pin as specified in Section 2.6
   of [RFC7469] with regard to user defined trust anchors.  The overall
   authentication result SHOULD only be considered successful if both
   authentication mechanisms are successful.

6.5.  Authentication in Opportunistic Privacy

   An Opportunistic Security [RFC7435] profile is described in [RFC7858]
   which MAY be used for DNS-over-(D)TLS.

   DNS clients issuing queries under an opportunistic profile and which
   know authentication information for a given privacy-enabling DNS
   server SHOULD try to authenticate the server using the mechanisms
   described here.  This is useful for detecting (but not preventing)
   active attack, since the fact that authentication information is
   available indicates that the server in question is a privacy-enabling
   DNS server to which it should be possible to establish an
   authenticated and encrypted connection.  In this case, whilst a
   client cannot know the reason for an authentication failure, from a
   security standpoint the client should consider an active attack in
   progress and proceed under that assumption.  For example, a client
   that implements a nameserver selection algorithm that preferentially
   uses nameservers which successfully authenticated (see Section 5)
   might not continue to use the failing server if there were
   alternative servers available.

   Attempting authentication is also useful for debugging or diagnostic
   purposes if there are means to report the result.  This information
   can provide a basis for a DNS client to switch to (preferred) Strict
   Privacy where it is viable e.g, where all the configured servers
   support DNS-over-(D)TLS and successfully authenticate.





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6.6.  Authentication in Strict Privacy

   To authenticate a privacy-enabling DNS server, a DNS client needs to
   know authentication information for each server it is willing to
   contact.  This is necessary to protect against active attacks which
   attempt to re-direct clients to rogue DNS servers.

   A DNS client requiring Strict Privacy MUST either use one of the
   sources listed in Section 7 to obtain an authentication domain name
   for the server it contacts, or use an SPKI pinset as described in
   [RFC7858].

   A DNS client requiring Strict Privacy MUST only attempt to connect to
   DNS servers for which at least one piece of authentication
   information is known.  The client MUST use the available verification
   mechanisms described in Section 8 to authenticate the server, and
   MUST abort connections to a server when no verification mechanism
   succeeds.

   With Strict Privacy, the DNS client MUST NOT commence sending DNS
   queries until at least one of the privacy-enabling DNS servers
   becomes available.

   A privacy-enabling DNS server may be temporarily unavailable when
   configuring a network.  For example, for clients on networks that
   require registration through web-based login (a.k.a. "captive
   portals"), such registration may rely on DNS interception and
   spoofing.  Techniques such as those used by DNSSEC-trigger
   [dnssec-trigger] MAY be used during network configuration, with the
   intent to transition to the designated privacy-enabling DNS servers
   after captive portal registration.  If using a Strict Usage profile
   the system MUST alert by some means that the DNS is not private
   during such bootstrap.

6.7.  Implementation guidance

   Section 9 describes the (D)TLS profile for DNS-over(D)TLS.
   Additional considerations relating to general implementation
   guidelines are discussed in both Section 11 and in Appendix A.

7.  Sources of Authentication Domain Names

7.1.  Full direct configuration

   DNS clients may be directly and securely provisioned with the
   authentication domain name of each privacy-enabling DNS server.  For
   example, using a client specific configuration file or API.




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   In this case, direct configuration for a DNS client would consist of
   both an IP address and an authentication domain name for each DNS
   server.

7.2.  Direct configuration of ADN only

   A DNS client may be configured directly and securely with only the
   authentication domain name of each of its privacy-enabling DNS
   servers.  For example, using a client specific configuration file or
   API.

   A DNS client might learn of a default recursive DNS resolver from an
   untrusted source (such as DHCP's DNS server option [RFC3646]).  It
   can then use Opportunistic DNS connections to an untrusted recursive
   DNS resolver to establish the IP address of the intended privacy-
   enabling DNS resolver by doing a lookup of A/AAAA records.  Private
   DNS resolution can now be done by the DNS client against the pre-
   configured privacy-enabling DNS resolver, using the IP address
   gathered from the untrusted DNS resolver.

   A DNS client so configured that successfully connects to a privacy-
   enabling DNS server MAY choose to locally cache the server host IP
   addresses in order to not have to repeat the opportunistic lookup.

7.3.  Dynamic discovery of ADN

   This section discusses the general case of a DNS client discovering
   both the authentication domain name and IP address dynamically.  This
   is not possible at the time of writing by any standard means.
   However since, for example, a future DHCP extension could (in
   principle) provide this mechanism the required security properties of
   such mechanisms are outlined here.

   When using a Strict profile the dynamic discovery technique used as a
   source of authentication domain names MUST be considered secure and
   trustworthy.  This requirement does not apply when using an
   Opportunistic profile given the security expectation of that profile.

7.3.1.  DHCP

   In the typical case today, a DHCP server [RFC2131] [RFC3315] provides
   a list of IP addresses for DNS resolvers (see Section 3.8 of
   [RFC2132]), but does not provide an authentication domain name for
   the DNS resolver, thus preventing the use of most of the
   authentication methods described here (all those that are based on a
   mechanism with ADN in Table 2).





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   This document does not specify or request any DHCP extension to
   provide authentication domain names.  However, if one is developed in
   future work the issues outlined in Section 8 of [RFC7227] should be
   taken into account as should the Security Considerations in
   Section 23 of [RFC3315]).

   This document does not attempt to describe secured and trusted
   relationships to DHCP servers, which is a purely DHCP issue (still
   open, at the time of writing.)  Whilst some implementation work is in
   progress to secure IPv6 connections for DHCP, IPv4 connections have
   received little to no implementation attention in this area.

8.  Authentication Domain Name based Credential Verification

8.1.  PKIX Certificate Based Authentication

   When a DNS client configured with an authentication domain name
   connects to its configured DNS server over (D)TLS, the server may
   present it with a PKIX certificate.  In order to ensure proper
   authentication, DNS clients MUST verify the entire certification path
   per [RFC5280].  The DNS client additionally uses [RFC6125] validation
   techniques to compare the domain name to the certificate provided.

   A DNS client constructs one Reference Identifier for the server based
   on the authentication domain name: A DNS-ID which is simply the
   authentication domain name itself.

   If the Reference Identifier is found in the PKIX certificate's
   subjectAltName extension as described in section 6 of [RFC6125], the
   DNS client should accept the certificate for the server.

   A compliant DNS client MUST only inspect the certificate's
   subjectAltName extension for the Reference Identifier.  In
   particular, it MUST NOT inspect the Subject field itself.

8.2.  DANE

   DANE [RFC6698] provides mechanisms to anchor certificate and raw
   public key trust with DNSSEC.  However this requires the DNS client
   to have an authentication domain name for the DNS Privacy Server
   which must be obtained via a trusted source.

   This section assumes a solid understanding of both DANE [RFC6698] and
   DANE Operations [RFC7671].  A few pertinent issues covered in these
   documents are outlined here as useful pointers, but familiarity with
   both these documents in their entirety is expected.

   It is noted that [RFC6698] says



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      "Clients that validate the DNSSEC signatures themselves MUST use
      standard DNSSEC validation procedures.  Clients that rely on
      another entity to perform the DNSSEC signature validation MUST use
      a secure mechanism between themselves and the validator."

   It is noted that [RFC7671] covers the following topics:

   o  Section 4.1: Opportunistic Security and PKIX Usages and
      Section 14: Security Considerations, which both discuss the use of
      Trust Anchor and End Entity based schemes (PKIX-TA(0) and PKIX-
      EE(1) respectively) for Opportunistic Security.

   o  Section 5: Certificate-Usage-Specific DANE Updates and Guidelines.
      Specifically Section 5.1 which outlines the combination of
      Certificate Usage DANE-EE(3) and Selector Usage SPKI(1) with Raw
      Public Keys [RFC7250].  Section 5.1 also discusses the security
      implications of this mode, for example, it discusses key lifetimes
      and specifies that validity period enforcement is based solely on
      the TLSA RRset properties for this case.

   o  Section 13: Operational Considerations, which discusses TLSA TTLs
      and signature validity periods.

   The specific DANE record for a DNS Privacy Server would take the
   form:

      _853._tcp.[authentication-domain-name] for TLS

      _853._udp.[authentication-domain-name] for DTLS

8.2.1.  Direct DNS Lookup

   The DNS client MAY choose to perform the DNS lookups to retrieve the
   required DANE records itself.  The DNS queries for such DANE records
   MAY use Opportunistic encryption or be in the clear to avoid trust
   recursion.  The records MUST be validated using DNSSEC as described
   above in [RFC6698].

8.2.2.  TLS DNSSEC Chain extension

   The DNS client MAY offer the TLS extension described in
   [I-D.ietf-tls-dnssec-chain-extension].  If the DNS server supports
   this extension, it can provide the full chain to the client in the
   handshake.

   If the DNS client offers the TLS DNSSEC Chain extension, it MUST be
   capable of validating the full DNSSEC authentication chain down to
   the leaf.  If the supplied DNSSEC chain does not validate, the client



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   MUST ignore the DNSSEC chain and validate only via other supplied
   credentials.

9.  (D)TLS Protocol Profile

   This section defines the (D)TLS protocol profile of DNS-over-(D)TLS.

   Clients and servers MUST adhere to the (D)TLS implementation
   recommendations and security considerations of [RFC7525] except with
   respect to (D)TLS version.

   Since encryption of DNS using (D)TLS is a green-field deployment DNS
   clients and servers MUST implement only (D)TLS 1.2 or later.  For
   example, implementing TLS 1.3 [I-D.ietf-tls-tls13] is also an option.

   Implementations MUST NOT offer or provide TLS compression, since
   compression can leak significant amounts of information, especially
   to a network observer capable of forcing the user to do an arbitrary
   DNS lookup in the style of the CRIME attacks [CRIME].

   Implementations compliant with this profile MUST implement all of the
   following items:

   o  TLS session resumption without server-side state [RFC5077] which
      eliminates the need for the server to retain cryptographic state
      for longer than necessary (This statement updates [RFC7858]).

   o  Raw public keys [RFC7250] which reduce the size of the
      ServerHello, and can be used by servers that cannot obtain
      certificates (e.g., DNS servers on private networks).  A client
      MUST only indicate support for raw public keys if it has an SPKI
      pinset pre-configured (for interoperability reasons).

   Implementations compliant with this profile SHOULD implement all of
   the following items:

   o  TLS False Start [RFC7918] which reduces round-trips by allowing
      the TLS second flight of messages (ChangeCipherSpec) to also
      contain the (encrypted) DNS query.

   o  Cached Information Extension [RFC7924] which avoids transmitting
      the server's certificate and certificate chain if the client has
      cached that information from a previous TLS handshake.

   Guidance specific to TLS is provided in [RFC7858] and that specific
   to DTLS it is provided in [RFC8094].





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10.  IANA Considerations

   This memo includes no request to IANA.

11.  Security Considerations

   Security considerations discussed in [RFC7525], [RFC8094] and
   [RFC7858] apply to this document.

   DNS Clients SHOULD implement support for the mechanisms described in
   Section 8.2 and offering a configuration option which limits
   authentication to using only those mechanisms (i.e., with no fallback
   to pure PKIX based authentication) such that authenticating solely
   via the PKIX infrastructure can be avoided.

11.1.  Counter-measures to DNS Traffic Analysis

   This section makes suggestions for measures that can reduce the
   ability of attackers to infer information pertaining to encrypted
   client queries by other means (e.g., via an analysis of encrypted
   traffic size, or via monitoring of resolver to authoritative
   traffic).

   DNS-over-(D)TLS clients and servers SHOULD implement the following
   relevant DNS extensions

   o  EDNS(0) padding [RFC7830], which allows encrypted queries and
      responses to hide their size making analysis of encrypted traffic
      harder.

   Guidance on padding policies for EDNS(0) is provided in
   [I-D.ietf-dprive-padding-policy]

   DNS-over-(D)TLS clients SHOULD implement the following relevant DNS
   extensions

   o  Privacy Election using Client Subnet in DNS Queries [RFC7871].  If
      a DNS client does not include an EDNS0 Client Subnet Option with a
      SOURCE PREFIX-LENGTH set to 0 in a query, the DNS server may
      potentially leak client address information to the upstream
      authoritative DNS servers.  A DNS client ought to be able to
      inform the DNS Resolver that it does not want any address
      information leaked, and the DNS Resolver should honor that
      request.







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12.  Acknowledgments

   Thanks to the authors of both [RFC8094] and [RFC7858] for laying the
   ground work that this draft builds on and for reviewing the contents.
   The authors would also like to thank John Dickinson, Shumon Huque,
   Melinda Shore, Gowri Visweswaran, Ray Bellis, Stephane Bortzmeyer,
   Jinmei Tatuya, Paul Hoffman, Christian Huitema and John Levine for
   review and discussion of the ideas presented here.

13.  References

13.1.  Normative References

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

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
              January 2008, <http://www.rfc-editor.org/info/rfc5077>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [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,
              <http://www.rfc-editor.org/info/rfc5280>.

   [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, <http://www.rfc-editor.org/info/rfc6125>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://www.rfc-editor.org/info/rfc6347>.







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   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <http://www.rfc-editor.org/info/rfc6698>.

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <http://www.rfc-editor.org/info/rfc7250>.

   [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, <http://www.rfc-editor.org/info/rfc7525>.

   [RFC7671]  Dukhovni, V. and W. Hardaker, "The DNS-Based
              Authentication of Named Entities (DANE) Protocol: Updates
              and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
              October 2015, <http://www.rfc-editor.org/info/rfc7671>.

   [RFC7830]  Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
              DOI 10.17487/RFC7830, May 2016,
              <http://www.rfc-editor.org/info/rfc7830>.

   [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, <http://www.rfc-editor.org/info/rfc7858>.

   [RFC7918]  Langley, A., Modadugu, N., and B. Moeller, "Transport
              Layer Security (TLS) False Start", RFC 7918,
              DOI 10.17487/RFC7918, August 2016,
              <http://www.rfc-editor.org/info/rfc7918>.

   [RFC7924]  Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", RFC 7924,
              DOI 10.17487/RFC7924, July 2016,
              <http://www.rfc-editor.org/info/rfc7924>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <http://www.rfc-editor.org/info/rfc8094>.






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13.2.  Informative References

   [CRIME]    Rizzo, J. and T. Duong, "The CRIME Attack", 2012.

   [dnssec-trigger]
              NLnetLabs, "Dnssec-Trigger", May 2014,
              <https://www.nlnetlabs.nl/projects/dnssec-trigger/>.

   [I-D.ietf-dprive-padding-policy]
              Mayrhofer, A., "Padding Policy for EDNS(0)", draft-ietf-
              dprive-padding-policy-00 (work in progress), December
              2016.

   [I-D.ietf-tls-dnssec-chain-extension]
              Shore, M., Barnes, R., Huque, S., and W. Toorop, "A DANE
              Record and DNSSEC Authentication Chain Extension for TLS",
              draft-ietf-tls-dnssec-chain-extension-04 (work in
              progress), June 2017.

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-20 (work in progress),
              April 2017.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <http://www.rfc-editor.org/info/rfc2131>.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
              <http://www.rfc-editor.org/info/rfc2132>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              DOI 10.17487/RFC3646, December 2003,
              <http://www.rfc-editor.org/info/rfc3646>.

   [RFC7227]  Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
              S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
              BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
              <http://www.rfc-editor.org/info/rfc7227>.





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   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <http://www.rfc-editor.org/info/rfc7435>.

   [RFC7469]  Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
              Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
              2015, <http://www.rfc-editor.org/info/rfc7469>.

   [RFC7626]  Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
              DOI 10.17487/RFC7626, August 2015,
              <http://www.rfc-editor.org/info/rfc7626>.

   [RFC7871]  Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", RFC 7871,
              DOI 10.17487/RFC7871, May 2016,
              <http://www.rfc-editor.org/info/rfc7871>.

Appendix A.  Server capability probing and caching by DNS clients

   This section presents a non-normative discussion of how DNS clients
   might probe for and cache capabilities of privacy-enabling DNS
   servers.

   Deployment of both DNS-over-TLS and DNS-over-DTLS will be gradual.
   Not all servers will support one or both of these protocols and the
   well-known port might be blocked by some middleboxes.  Clients will
   be expected to keep track of servers that support DNS-over-TLS and/or
   DNS-over-DTLS, and those that have been previously authenticated.

   If no server capability information is available then (unless
   otherwise specified by the configuration of the DNS client) DNS
   clients that implement both TLS and DTLS should try to authenticate
   using both protocols before failing or falling back to a
   unauthenticated or clear text connections.  DNS clients using an
   Opportunistic Usage profile should try all available servers
   (possibly in parallel) in order to obtain an authenticated and
   encrypted connection before falling back.  (RATIONALE: This approach
   can increase latency while discovering server capabilities but
   maximizes the chance of sending the query over an authenticated and
   encrypted connection.)

Appendix B.  Changes between revisions

   [Note to RFC Editor: please remove this section prior to
   publication.]






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B.1.  -10 version

   Clarified the specific attacks the Usage profiles mitigate against.

   Revised wording in the draft relating 'security/privacy guarantees'
   and generally improved consistency of wording throughout the
   document.

   Corrected and added a number of references:

   o  RFC7924 is now Normative

   o  RFC7918 and RFC8094 are now Normative (and therefore Downrefs)

   o  draft-ietf-tls-tls13, draft-ietf-dprive-padding-policy,RFC3315 and
      RFC7227 added

   Terminology: Update definition of Privacy-enabling DNS server and
   moved normative definition to section 4.

   Section 5 and 6.3: Included discussion of the additional attacks
   possible when using meta-queries to bootstrap the DNS service

   Section 5: Added sentence on why Opportunistic Profile may fallback
   for latency reasons.

   Section 5.1: Added discussion of when clients might change Usage
   Profiles.

   Section 6.4: Added caveat on use of combined authentication re
   RFC7469.

   Section 6.5: Added more detail on how authentication results might be
   used in Opportunistic.  Opportunistic clients now SHOULD try for the
   best case.

   Section 7.3: Re-worked this section and the discussion of DHCP.

   Section 9: Removed unnecessary text, added condition on use of
   RFC7250 (Raw public keys).

   Section 11.: More detail on padding policies.

   Numerous editorial corrections.







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B.2.  -09 version

   Remove the SRV record to simplify the draft.

   Add suggestion that clients offer option to avoid using only PKIX
   authentication.

   Clarify that the MUST on implementing TLS session resumption updates
   RFC7858.

   Update page header to be '(D)TLS Authentication for TLS'.

B.3.  -08 version

   Removed hard failure as an option for Opportunistic Usage profile.

   Added a new section comparing the Authentication Mechanisms

B.4.  -07 version

   Re-work of the Abstract and Introduction to better describe the
   contents in this version.

   Terminology: New definition of 'authentication information'.

   Scope: Changes to the Scope section.

   Moved discussion of combining authentication mechanism earlier.

   Changes to the section headings and groupings to make the
   presentation more logical.

B.5.  -06 version

   Introduction: Re-word discussion of Working group charter.

   Introduction: Re-word first and third bullet point about 'obtaining'
   a domain name and IP address.

   Introduction: Update reference to DNS-over-TLS draft.

   Terminology: Change forwarder/proxy to just forwarder

   Terminology: Add definition of 'Authentication domain name' and use
   this throughout

   Section 4.2: Remove parenthesis in the table.




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   Section 4.2: Change the text after the table as agreed with Paul
   Hoffman.

   Section 4.3.1: Change title and remove brackets around last
   statement.

   Section 11: Split second paragraph.

B.6.  -05 version

   Add more details on detecting passive attacks to section 4.2

   Changed X.509 to PKIX throughout

   Change comment about future I-D on usage policies.

B.7.  -04 version

   Introduction: Add comment that DNS-over-DTLS draft is Experiments

   Update 2 I-D references to RFCs.

B.8.  -03 version

   Section 9: Update DANE section with better references to RFC7671 and
   RFC7250

B.9.  -02 version

   Introduction: Added paragraph on the background and scope of the
   document.

   Introduction and Discussion: Added more information on what a Usage
   profiles is (and is not) the the two presented here.

   Introduction: Added paragraph to make a comparison with the Strict
   profile in RFC7858 clearer.

   Section 4.2: Re-worked the description of Opportunistic and the
   table.

   Section 8.3: Clarified statement about use of DHCP in Opportunistic
   profile

   Title abbreviated.






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B.10.  -01 version

   Section 4.2: Make clear that the Strict Privacy Profile can include
   meta queries performed using Opportunistic Privacy.

   Section 4.2, Table 1: Update to clarify that Opportunistic Privacy
   does not guarantee protection against passive attack.

   Section 4.2: Add sentence discussing client/provider trusted
   relationships.

   Section 5: Add more discussion of detection of active attacks when
   using Opportunistic Privacy.

   Section 8.2: Clarify description and example.

B.11.  draft-ietf-dprive-dtls-and-tls-profiles-00

   Re-submission of draft-dgr-dprive-dtls-and-tls-profiles with name
   change to draft-ietf-dprive-dtls-and-tls-profiles.  Also minor nits
   fixed.

Authors' Addresses

   Sara Dickinson
   Sinodun Internet Technologies
   Magdalen Centre
   Oxford Science Park
   Oxford  OX4 4GA
   UK

   Email: sara@sinodun.com
   URI:   http://sinodun.com


   Daniel Kahn Gillmor
   ACLU
   125 Broad Street, 18th Floor
   New York  NY 10004
   USA

   Email: dkg@fifthhorseman.net









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

   Email: TirumaleswarReddy_Konda@McAfee.com












































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