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Versions: (draft-reddy-dprive-dprive-privacy-policy) 00 02

ADD WG                                                          T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                                 D. Wing
Expires: November 28, 2020                                        Citrix
                                                           M. Richardson
                                                Sandelman Software Works
                                                            M. Boucadair
                                                                  Orange
                                                            May 27, 2020


   DNS Server Selection: DNS Server Information with Assertion Token
               draft-reddy-add-server-policy-selection-02

Abstract

   The document defines a mechanism that allows communication of DNS
   resolver information to DNS clients for use in server selection
   decisions.  In particular, the document defines a mechanism for a DNS
   server to communicate its filtering policy and privacy statement URL
   to DNS clients.  This information is cryptographically signed to
   attest its authenticity.  Such information is used for the selection
   of DNS resolvers.  Typically, evaluating the DNS privacy statement,
   filtering policy, and the signatory, DNS clients with minimum human
   intervention can select the DNS server that best supports the user's
   desired privacy and filtering policy.

   This assertion is useful for encrypted DNS (e.g., DNS-over-TLS and
   DNS-over-HTTPS) servers that are either public resolvers or are
   discovered in a local network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 28, 2020.




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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
   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.  Sample Use Cases  . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Policy Assertion Token (PAT): Overview  . . . . . . . . . . .   5
   5.  PAT Header  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  'typ' (Type) Header Parameter . . . . . . . . . . . . . .   6
     5.2.  'alg' (Algorithm) Header Parameter  . . . . . . . . . . .   7
     5.3.  'x5u' (X.509 URL) Header Parameter  . . . . . . . . . . .   7
     5.4.  An Example of PAT Header  . . . . . . . . . . . . . . . .   7
   6.  PAT Payload . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  JWT Defined Claims  . . . . . . . . . . . . . . . . . . .   8
       6.1.1.  'iat' - Issued At Claim . . . . . . . . . . . . . . .   8
       6.1.2.  'exp' - Expiration Time Claim . . . . . . . . . . . .   8
     6.2.  PAT Specific Claims . . . . . . . . . . . . . . . . . . .   8
       6.2.1.  DNS Server Identity Claims  . . . . . . . . . . . . .   9
       6.2.2.  'policyinfo' (Policy Information) Claim . . . . . . .   9
       6.2.3.  Example . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  PAT Signature . . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  Extending PAT . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  Deterministic JSON Serialization  . . . . . . . . . . . . . .  12
     9.1.  Example PAT Deterministic JSON Form . . . . . . . . . . .  12
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  13
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     12.1.  Media Type Registration  . . . . . . . . . . . . . . . .  14
       12.1.1.  Media Type Registry Contents Additions Requested . .  14
     12.2.  JSON Web Token Claims Registration . . . . . . . . . . .  15
       12.2.1.  Registry Contents Additions Requested  . . . . . . .  15
     12.3.  DNS Resolver Information Registration  . . . . . . . . .  16
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16



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     14.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     14.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Appendix A.  Example ES256 based PAT JWS Serialization and
                Signature  . . . . . . . . . . . . . . . . . . . . .  19
     A.1.  X.509 Private Key in PKCS#8 Format for ES256 Example**  .  21
     A.2.  X.509 Public Key for ES256 Example**  . . . . . . . . . .  21
   Appendix B.  Complete JWS JSON Serialization Representation with
                multiple Signatures  . . . . . . . . . . . . . . . .  21
     B.1.  X.509 Private Key in PKCS#8 format for E384 Example** . .  22
     B.2.  X.509 Public Key for ES384 Example**  . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   [RFC7626] discusses DNS privacy considerations in both "on the wire"
   (Section 2.4 of [RFC7626]) and "in the server" (Section 2.5 of
   [RFC7626]) contexts.  Examples of protocols that provide encrypted
   channels between DNS clients and servers are DNS-over-HTTPS (DoH)
   [RFC8484] and DNS-over-TLS (DoT) [RFC7858].

   DNS clients can discover and authenticate encrypted DNS (e.g., DoH
   and DoT) servers provided by a local network, for example using the
   techniques proposed in [I-D.btw-add-home].  If the mechanism used to
   discover the encrypted DNS server is insecure, the DNS client needs
   evidence about the encrypted server to assess its trustworthiness and
   a way to appraise such evidence.  The mechanism specified in this
   document can be used by the DNS client to cryptographically identify
   it is connecting to an encrypted DNS server hosted by a specific
   organization (e.g., ISP or Enterprise).

   The DNS Recursive Operator Privacy (DROP) statement explained in
   [I-D.ietf-dprive-bcp-op] outlines the recommended contents a DNS
   operator should publish, thereby providing a means for users to
   evaluate the privacy properties of a given DNS service.  While a
   human can review the privacy statement of a DNS server operator, the
   challenge is the user has to search to find the URL that points to
   the human readable privacy policy information of the DNS server.
   Also, a user does not know if a DNS server (public or local) performs
   DNS-based content filtering.

   This document simplifies the user experience by supporting a
   mechanism to retrieve the DNS server policy permitting the user to
   review human-readable privacy policy information of the DNS server
   and to assess whether that DNS server performs DNS-based content
   filtering.

   This document also defines a mechanism for DNS clients to gather a
   set of information related to discovered (or pre-configured) servers



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   and use that information to feed a DNS server selection procedure.
   The following parameters are supported in this version:

   Malware blocking:  Indicates whether the DNS server offers malware
      blocking service.

   Policy blocking:  Indicates whether the DNS server maintains a block-
      list (e.g., imposed by regulation).

   QNAME minimization:  Indicates whether the DNS server implements
      QNAME minimisation [RFC7816].

   The cryptographically signed policy allows a DNS client to, e.g.,
   connect to multiple DNS servers and prompt the user to review the DNS
   privacy statements to select the DNS server that adheres to the
   privacy preserving data policy and DNS filtering expectations of the
   user.  How a user instructs a DNS client about his/her preferences
   and how/whether the DNS client prompts a user are out of scope.

2.  Sample Use Cases

   The mechanism for a DNS server to communicate its cryptographically
   signed policies to DNS clients contributes to solve the following
   problems in various deployments:

   o  The encrypted DNS server advertised using DHCP/RA in Home and
      Mobile networks is insecure, the mechanism specified in this
      document can be used by the DNS client to validate the signatory
      (e.g., cryptographically attested by the ISP).

   o  Typically Enterprise networks do not assume that all devices in
      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.  The mechanism specified in this
      document can be used by users of the BYOD devices to determine if
      the DNS server on the local network complies with their user's
      privacy policy and DNS filtering expectations.

   o  The user selects specific well-known networks (e.g., organization
      for which a user works or a user works temporarily within another
      corporation) to learn the privacy policy statement and filtering
      policy of the local DNS server.  If the discovered encrypted DNS
      server does not meet the privacy preserving data policy and
      filtering requirements of the user, the DNS client can take
      appropriate actions.  For example, the action can be to use the
      discovered DNS server only to access internal-only DNS names and
      use another DNS server (adhering with the user's expectations) for
      public domains.



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   o  The policy information signals the presence of DNS-based content
      filtering in the attached network.  If the network is well-known
      to the DNS client and the local DNS server meets the privacy
      requirements of the user, the DNS client can continue to use
      encrypted connection with the local encrypted DNS server.  If the
      error code returned by the DNS server indicates access to the
      domain is blocked because of internal security policy
      [I-D.ietf-dnsop-extended-error], the DNS client can securely
      identify access to the domain is censored by the network.

   o  The signed policy contains an URL that points to a human-readable
      privacy policy information of the DNS server for the user to
      review and can make an informed decision whether the DNS server is
      trustworthy to honor the privacy of the user.  The DNS Push
      Notifications mechanism defined in [I-D.ietf-dnssd-push] can be
      used by the DNS client to be asynchronously notified when the
      policy change occurs.  The client automatically learns updates to
      the policy of the DNS server, and whenever the privacy statement
      of the DNS server changes, the client can notify the user to re-
      evaluate the updated privacy statement.  As a reminder, DNS Push
      Notification is only defined for TLS over TCP.  DNS client
      implementations that do not support DNS Push Notifications can use
      the mechanism discussed in Section 6.1.2 to identify policy
      updates.

3.  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].

   'DoH/DoT' refers to DNS-over-HTTPS and/or DNS-over-TLS.

   'Encrypted DNS' refers to a DNS protocol that provides an encrypted
   channel between a DNS client and server (e.g., DoT or DoH).

4.  Policy Assertion Token (PAT): Overview

   JSON Web Token (JWT) [RFC7519] and JSON Web Signature (JWS) [RFC7515]
   and related specifications define a standard token format that can be
   used as a way of encapsulating claimed or asserted information with
   an associated digital signature using X.509 based certificates.  JWT
   provides a set of claims in JSON format that can accommodate asserted



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   policy information of the DoH/DoT server.  Additionally, JWS provides
   a path for updating methods and cryptographic algorithms used for the
   associated digital signatures.

   JWS defines the use of JSON data structures in a specified canonical
   format for signing data corresponding to JOSE header, JWS Payload,
   and JWS Signature.  The next sections define the header and claims
   that MUST be minimally used with JWT and JWS for privacy assertion
   token.

   The Policy Assertion Token (PAT) specifically uses this token format
   and defines claims that convey the policy information of DoH/DoT
   server.  After the DoT/DoH session is established, the client can
   retrieve the PAT object using the RESINFO RRtype and QNAME of
   "resolver-info.arpa/IN" defined in [I-D.pp-add-resinfo].  The
   signature of PAT object can be validated by the DNS client.  If the
   signer and the contents of the PAT object comply with the user's
   requirements, the user's client software can use that DNS server.

   The PAT object is signed by the DNS server's domain that is
   authoritative to assert the DNS server policy information.  This
   authority is represented by the certificate credentials and the
   signature.

   For example, the PAT object could be created by the organization
   hosting the DoH/DoT server and optionally by a third party who
   performed privacy and security audit of the DoH/DoT server.  The DNS
   client needs to have the capability to verify the digital signature
   and to parse the PAT object.

5.  PAT Header

   The JWS token header is a JOSE header (Section 4 of [RFC7515]) that
   defines the type and encryption algorithm used in the token.

   PAT header MUST include, at a minimum, the header parameters defined
   in Sections 5.1, 5.2, and 5.3.

5.1.  'typ' (Type) Header Parameter

   The 'typ' (Type) Header Parameter is defined Section 4.1.9 of
   [RFC7515] to declare the media type of the complete JWS.

   For PAT Token the 'typ' header MUST be the string 'pat'.  This
   represents that the encoded token is a JWT of type pat.






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5.2.  'alg' (Algorithm) Header Parameter

   The 'alg' (Algorithm) Header Parameter is defined in Section 4.1.1 of
   [RFC7515].  It specifies the JWS signature cryptographic algorithm.
   It also refers to a list of defined 'alg' values as part of a
   registry established by JSON Web Algorithms (JWA) [RFC7518]
   Section 3.1.

   For the creation and verification of PAT tokens and their digital
   signatures, implementations MUST support ES256 as defined in
   Section 3.4 of [RFC7518].  Implementations MAY support other
   algorithms registered in the JSON Web Signature and Encryption
   Algorithms registry created by [RFC7518].  The content of that
   registry may be updated in the future depending on cryptographic
   strength requirements guided by current security best practice.  The
   mandatory-to-support algorithm for PAT tokens may likewise be updated
   in the future.

   Implementations of PAT digital signatures using ES256 as defined
   above SHOULD use deterministic ECDSA when supported for the reasons
   stated in [RFC6979].

5.3.  'x5u' (X.509 URL) Header Parameter

   As defined in Section 4.1.5 of [RFC7515], the 'x5u' header parameter
   defines a URI [RFC3986] referring to the resource for the X.509
   public key certificate or certificate chain [RFC5280] corresponding
   to the key used to digitally sign the JWS.  Generally, as defined in
   Section 4.1.5 of [RFC7515] this corresponds to an HTTPS or DNSSEC
   resource using integrity protection.

5.4.  An Example of PAT Header

   An example of the PAT header is shown in Figure 1.  It includes the
   specified PAT type, ES256 algorithm, and an URI referencing the
   network location of the certificate needed to validate the PAT
   signature.

   {
     "typ":"pat",
     "alg":"ES256",
     "x5u":"https://cert.example.com/pat.cer"
   }

                      Figure 1: A PAT Header Example






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6.  PAT Payload

   The token claims consists of the policy information of the DNS server
   which needs to be verified at the DNS client.  These claims follow
   the definition of a JWT claim (Secion 4 of [RFC7519]) and are encoded
   as defined by the JWS Payload (Section 3 of [RFC7515]).

   PAT defines the use of a standard JWT-defined claim as well as custom
   claims corresponding to the DoT or DoH servers.

   Claim names MUST use the US-ASCII character set.  Claim values MAY
   contain characters that are outside the ASCII range, however they
   MUST follow the default JSON serialization defined in Section 7 of
   [RFC7519].

6.1.  JWT Defined Claims

6.1.1.  'iat' - Issued At Claim

   The JSON claim MUST include the 'iat' (Section 4.1.6 of [RFC7519])
   defined claim "Issued At".  The 'iat' should be set to the date and
   time of issuance of the JWT.  The time value should be of the format
   (NumericDate) defined in Section 2 of [RFC7519].

6.1.2.  'exp' - Expiration Time Claim

   The JSON claim MUST include the 'exp' (Section 4.1.4 of [RFC7519])
   defined "claim Expiration Time".  The 'exp' should be set to specify
   the expiration time on or after which the JWT is not accepted for
   processing.  The PAT object should expire after a reasonable
   duration.  A short expiration time for the PAT object periodically
   reaffirms the policy information of the DNS server to the DNS client
   and ensures the DNS client does not use outdated policy information.
   If the DNS client knows the PAT object has expired, it should make
   another request to get the new PAT object from the DNS server.  For
   example, the client can compute a hash of the resolver information,
   retreive the information after the expiration time, computes the hash
   of the newly retrieved resolver information, and compares with the
   old hash to detect policy updates.  A quality implementation can
   perform automatic analysis and avoid presenting this information to
   the user if the DNS server's policies have not changed.

6.2.  PAT Specific Claims








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6.2.1.  DNS Server Identity Claims

   The DNS server identity is represented by a claim that is required
   for PAT: the 'server' claim.  The 'server' MUST contain claim values
   that are identity claim JSON objects where the child claim name
   represents an identity type and the claim value is the identity
   string, both defined in subsequent subsections.

   These identities can be represented as either authentication domain
   name (ADN) (defined in [RFC8310]) or Uniform Resource Indicators
   (URI).

   The DNS client constructs a reference identifier for the DNS server
   based on the ADN or the domain portion in the URI of the DNS server
   identity.  The domain name in the DNS-ID identifier type within
   subjectAltName entry in the DNS server certificate conveyed in the
   TLS handshake is matched with the reference identifier.  If the match
   is not successful, the client MUST not accept the PAT for further
   processing.

6.2.1.1.  'adn' - Authentication Domain Name Identity

   If the DNS server identity is an ADN, the claim name representing the
   identity MUST be 'adn'.  The claim value for the 'adn' claim is the
   ADN.

6.2.1.2.  'uri' - URI Identity

   If the DNS server identity is of the form URI, as defined in
   [RFC3986], the claim name representing the identity MUST be 'uri' and
   the claim value is the URI form of the DNS server identity.

   As a reminder, if DoH is supported by the DNS server, the DNS client
   uses the https URI scheme (Section 3 of [RFC8484]).

6.2.2.  'policyinfo' (Policy Information) Claim

   The 'policyinfo' claim MUST be formatted as a JSON object.  The
   'policyinfo' claim contains the policy information of the DNS server,
   it includes the following attributes:

   filtering:  If the DNS server changes some of the answers that it
      returns based on policy criteria, such as to prevent access to
      malware sites or objectionable content.  This optional attribute
      has the following structure:






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      malwareblocking:  The DNS server offers malware blocking service.
         If access to domains is blocked on threat data, the parameter
         value is set to 'true'.

      policyblocking:  If access to domains is blocked on a blacklist or
         objectionable content, the parameter value is set to 'true'.

   qnameminimization:  If the DNS server implements QNAME minimisation
      [RFC7816] to improve DNS privacy.  If the parameter value is set
      to 'true', QNAME minimisation is supported by the DNS server.
      This is a mandatory attribute.

   privacyurl:  A URL that points to the privacy policy information of
      the DNS server.  This is a mandatory attribute.

   auditurl:  A URL that points to the security (including privacy)
      assessment report of the DNS server by a third party auditor.
      This is an optional attribute.

6.2.3.  Example

   Figure 2 shows an example of policy information.

   {
     "server":{
         "adn":["example.com"]
     },
     "iat":1443208345,
     "exp":1443640345,
     "policyinfo": {
        "filtering": {
            "malwareblocking": true,
            "policyblocking": false
        },
        "qnameminimization":false,
        "privacyurl": "https://example.com/commitment-to-privacy/"
     }
   }

                Figure 2: An Example of Policy Information

7.  PAT Signature

   The signature of the PAT is created as specified in Section 5.1 of
   [RFC7515] (Steps 1 through 6).  PAT MUST use the JWS Protected
   Header.





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   For the JWS Payload and the JWS Protected Header, the lexicographic
   ordering and white space rules described in Section 5 and Section 6,
   and JSON serialization rules in Section 9 MUST be followed.

   The PAT is cryptographically signed by the domain hosting the DNS
   server and optionally by a third party who performed privacy and
   security audit of the DNS server.

   The policy information is attested using "Organization Validation"
   (OV) or "Extended Validation" (EV) certificates to avoid bad actors
   taking advantage of this mechanism to advertise encrypted DNS servers
   for illegitimate and fraudulent purposes meant to trick DNS clients
   into believing that they are using a legitimate encrypted DNS server
   hosted to provide privacy for DNS transactions.

   Alternatively, a DNS client has to be configured to trust the leaf of
   the signer of the PAT object.  That is, trust of the signer MUST NOT
   be determined by validating the signer via the OS or the browser
   trust chain because that would allow any arbitrary entity to operate
   a DNS server and assert any sort of policy.

   Appendix A provides an example of how to follow the steps to create
   the JWS Signature.

   JWS JSON serialization (Step 7 in Section 5.1 of [RFC7515]) is
   supported for PAT to enable multiple signatures to be applied to the
   PAT object.  For example, the PAT object can be cryptographically
   signed by the domain hosting the DNS server and by a third party who
   performed privacy and security audit of the DNS server.

   Appendix B includes an example of the full JWS JSON serialization
   representation with multiple signatures.

   Section 5.1 of [RFC7515] (Step 8) describes the method to create the
   final JWS Compact Serialization form of the PAT Token.

8.  Extending PAT

   PAT includes the minimum set of claims needed to securely assert the
   policy information of the DNS server.  JWT supports a mechanism to
   add additional asserted or signed information by simply adding new
   claims.  PAT can be extended beyond the defined base set of claims to
   represent other DNS server information requiring assertion or
   validation.  Specifying new claims follows the baseline JWT
   procedures (Section 10.1 of [RFC7519]).  Understanding new claims on
   the DNS client is optional.  The creator of a PAT object cannot
   assume that the DNS client will understand the new claims.




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9.  Deterministic JSON Serialization

   JSON objects can include spaces and line breaks, and key value pairs
   can occur in any order.  It is therefore a non-deterministic string
   format.  In order to make the digital signature verification work
   deterministically, the JSON representation of the JWS Protected
   Header object and JWS Payload object MUST be computed as follows.

   The JSON object MUST follow the following rules.  These rules are
   based on the thumbprint of a JSON Web Key (JWK) as defined in
   Section 3 of [RFC7638] (Step 1).

   1.  The JSON object MUST contain no whitespace or line breaks before
       or after any syntactic elements.

   2.  JSON objects MUST have the keys ordered lexicographically by the
       Unicode [UNICODE] code points of the member names.

   3.  JSON value literals MUST be lowercase.

   4.  JSON numbers are to be encoded as integers unless the field is
       defined to be encoded otherwise.

   5.  Encoding rules MUST be applied recursively to member values and
       array values.

9.1.  Example PAT Deterministic JSON Form

   This section demonstrates the deterministic JSON serialization for
   the example PAT Payload shown in Section 6.2.3.

   The initial JSON object is shown in Figure 3.

   {
     "server":{
         "adn":["example.com"]
     },
     "iat":1443208345,
     "exp":1443640345,
     "policyinfo": {
        "qnameminimization":false,
        "privacyurl": "https://example.com/commitment-to-privacy/"
     }
   }

                       Figure 3: Initial JSON Object





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   The parent members of the JSON object are as follows, in
   lexicographic order: "exp", "iat", "policyinfo", "server".

   The final constructed deterministic JSON serialization
   representation, with whitespace and line breaks removed, (with line
   breaks used for display purposes only) is:

{"exp":1443640345,"iat":1443208345,
"policyinfo":{"privacyurl":"https://example.com/commitment-to-privacy/",
"qnameminimization":false},"server":{"adn":["example.com"]}}

                     Figure 4: Deterministic JSON Form

10.  Privacy Considerations

   Users are expected to indicate to their system in some way that they
   trust certain PAT signers (e.g., if working for Example, Inc., the
   user's system is configured to trust "example.com" signing the PAT).
   By doing so, the DNS client can automatically discover encrypted DNS
   server in specific networks, validate the PAT signature and the user
   can check if the human readable privacy policy information of the DNS
   server complies with user's privacy needs, prior to using that
   encrypted DNS server for DNS queries.

   The DNS client MUST retrieve the human-readable privacy statement
   from the 'privacyurl' attribute to assist with that decision (e.g.,
   display the privacy statement when it changes, show differences in
   previously-retrieved version, etc.).  With the steps above, user can
   review the human-readable privacy policy information of the DoH/DoT
   server.

   Another scenario is bootstrapping a networking device to use the
   encrypted DNS server in the local network.  Secure Zero Touch
   Provisioning [RFC8572] defines a bootstrapping strategy for enabling
   devices to securely obtain the required configuration information
   with no user input.  If the encrypted DNS server is insecurely
   discovered and not pre-configured in the networking device, the
   client can validate the Policy Assertion Token signature using the
   owner certificate as per Section 3.2 of [RFC8572].

11.  Security Considerations

   The use of PAT object based on the validation of the digital
   signature and the associated certificate requires consideration of
   the authentication and authority or reputation of the signer to
   attest the policy information of the DNS server being asserted.  Bad
   actors can host encrypted DNS servers, and claim the servers offer
   privacy but exactly do the opposite to invade the privacy of the



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   user.  Bad actor can get a domain name, host encrypted DNS servers,
   and get the DNS server certificate signed by a CA.  The policy
   information will have to be attested using OV/EV certificates or a
   PAT object signer trusted by the DNS client to prevent the attack.

   The CA that issued the OV/EV certificate does not attest the resolver
   information.  The organization hosting the DNS server attests the
   resolver information using the OV/EV certificate and the client uses
   the OV/EV certificate to identify the organization (e.g., ISP or
   Enterprise) hosting the DNS server.

   If the PAT object is asserted by a third party, it can do a "time of
   check" but the DNS server is susceptible of "time of use" attack.
   For example, changes to the policy of the DNS server can cause a
   disagreement between the auditor and the DNS server operation, hence
   the PAT object needs to be also asserted by the domain hosting the
   DNS server.  In addition, the PAT object needs to have a short
   expiration time (e.g., 7 days) to ensure the DNS server's domain re-
   asserts the policy information and limits the damage from change in
   policy and mis-issuance.

12.  IANA Considerations

12.1.  Media Type Registration

12.1.1.  Media Type Registry Contents Additions Requested

   This section registers the 'application/pat' media type [RFC2046] in
   the 'Media Types' registry in the manner described in [RFC6838],
   which can be used to indicate that the content is a PAT defined JWT.

   o  Type name: application

   o  Subtype name: pat

   o  Required parameters: n/a

   o  Optional parameters: n/a

   o  Encoding considerations: 8bit; application/pat values are encoded
      as a series of base64url-encoded values (some of which may be the
      empty string) separated by period ('.') characters..

   o  Security considerations: See the Security Considerations
      Section of [RFC7515].

   o  Interoperability considerations: n/a




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   o  Published specification: [TODO this document]

   o  Applications that use this media type: DNS

   o  Fragment identifier considerations: n/a

   o  Additional information:

      Magic number(s): n/a File extension(s): n/a Macintosh file type
      code(s): n/a

   o  Person & email address to contact for further information:
      Tirumaleswar Reddy, kondtir@gmail.com

   o  Intended usage: COMMON

   o  Restrictions on usage: none

   o  Author: Tirumaleswar Reddy, kondtir@gmail.com

   o  Change Controller: IESG

   o  Provisional registration?  No

12.2.  JSON Web Token Claims Registration

12.2.1.  Registry Contents Additions Requested

   o  Claim Name: 'server'

   o  Claim Description: DNS server identity

   o  Change Controller: IESG

   o  Specification Document(s): Section 6.2.1 of [TODO this document]

   o  Claim Name: 'policyinfo'

   o  Claim Description: Policy information of DNS server.

   o  Change Controller: IESG

   o  Specification Document(s): Section 6.2.2 of [TODO this document]








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12.3.  DNS Resolver Information Registration

   IANA will add the names filtering, qnameminimization, privacyurl and
   auditurl to the DNS Resolver Information registry defined in
   Section 4.2 of [I-D.pp-add-resinfo].

13.  Acknowledgments

   This specification leverages some of the work that has been done in
   [RFC8225].  Thanks to Ted Lemon, Paul Wouters, Neil Cook and Shashank
   Jain for the discussion and comments.

14.  References

14.1.  Normative References

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/info/rfc2046>.

   [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>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [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>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [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>.





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   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <https://www.rfc-editor.org/info/rfc7638>.

   [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>.

   [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>.

   [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>.

14.2.  Informative References

   [I-D.btw-add-home]
              Boucadair, M., Reddy.K, T., Wing, D., and N. Cook,
              "Encrypted DNS Discovery and Deployment Considerations for
              Home Networks", draft-btw-add-home-06 (work in progress),
              May 2020.

   [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.






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   [I-D.ietf-dnsop-terminology-ter]
              Hoffman, P., "Terminology for DNS Transports and
              Location", draft-ietf-dnsop-terminology-ter-01 (work in
              progress), February 2020.

   [I-D.ietf-dnssd-push]
              Pusateri, T. and S. Cheshire, "DNS Push Notifications",
              draft-ietf-dnssd-push-25 (work in progress), October 2019.

   [I-D.ietf-dprive-bcp-op]
              Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A.
              Mankin, "Recommendations for DNS Privacy Service
              Operators", draft-ietf-dprive-bcp-op-09 (work in
              progress), May 2020.

   [I-D.pp-add-resinfo]
              Sood, P. and P. Hoffman, "DNS Resolver Information Self-
              publication", draft-pp-add-resinfo-01 (work in progress),
              May 2020.

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

   [RFC7816]  Bortzmeyer, S., "DNS Query Name Minimisation to Improve
              Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
              <https://www.rfc-editor.org/info/rfc7816>.

   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
              <https://www.rfc-editor.org/info/rfc8225>.

   [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>.

   [RFC8572]  Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
              Touch Provisioning (SZTP)", RFC 8572,
              DOI 10.17487/RFC8572, April 2019,
              <https://www.rfc-editor.org/info/rfc8572>.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard", June 2016,
              <http://www.unicode.org/versions/latest/>.







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Appendix A.  Example ES256 based PAT JWS Serialization and Signature

   For PAT, there will always be a JWS with the following members:

   o  'protected', with the value BASE64URL(UTF8(JWS Protected Header))

   o  'payload', with the value BASE64URL (JWS Payload)

   o  'signature', with the value BASE64URL(JWS Signature)

   This example will follow the steps in JWS [RFC7515] Section 5.1,
   steps 1-6 and 8 and incorporates the additional serialization steps
   required for PAT.

   Step 1 for JWS references the JWS Payload, an example PAT Payload is
   as follows:

   {
     "server":{
         "adn":["example.com"]
     },
     "iat":1443208345,
     "exp":1443640345,
     "policyinfo": {
        "filtering": {
            "malwareblocking": true,
            "policyblocking": false
        },
        "qnameminimization":false,
        "privacyurl": "https://example.com/commitment-to-privacy/"
     }
   }

   This would be serialized to the form (with line break used for
   display purposes only):

   {"exp":1443640345,"iat":1443208345,"policyinfo":{
   "filtering":{"malwareblocking": true,"policyblocking": false},
   "privacyurl":"https://example.com/commitment-to-privacy/",
   "qnameminimization":false},"server":{"adn":["example.com"]}}

   Step 2 Computes the BASE64URL(JWS Payload) producing this value (with
   line break used for display purposes only):








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   eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6e
   yJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9ja2
   luZyI6ZmFsc2V9LCJwcml2YWN5dXJsIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9jb21
   taXRtZW50LXRvLXByaXZhY3kvIiwicW5hbWVtaW5pbWl6YXRpb24iOmZhbHNlfSwi
   c2VydmVyIjp7ImFkbiI6WyJleGFtcGxlLmNvbSJdfX0



   For Step 3, an example PAT Protected Header comprising the JOSE
   Header is as follows:

   {
     "alg":"ES256",
     "typ":"pat",
     "x5u":"https://cert.example.com/pat.cer"
   }

   This would be serialized to the form (with line break used for
   display purposes only):

   {"alg":"ES256","typ":"pat","x5u":"https://cert.example.com
   /pat.cer"}

   Step 4 Performs the BASE64URL(UTF8(JWS Protected Header)) operation
   and encoding produces this value (with line break used for display
   purposes only):

   eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
   eGFtcGxlLmNvbS9wYXQuY2VyIn0



   Step 5 and Step 6 performs the computation of the digital signature
   of the PAT Signing Input ASCII(BASE64URL(UTF8(JWS Protected
   Header)) || '.' || BASE64URL(JWS Payload)) using ES256 as the
   algorithm and the BASE64URL(JWS Signature).

   4vQEAF_Vlp1Tr6sJmS4pnIKDRmIjH8EZzY5BMT2qJCHD8PmjBktWVnlmbmyHs05G
   KauRBdIFnfp3oDPbE0Jq4w


   Step 8 describes how to create the final PAT token, concatenating the
   values in the order Header.Payload.Signature with period ('.')
   characters.  For the above example values this would produce the
   following (with line breaks between period used for readability
   purposes only):





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   eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
   eGFtcGxlLmNvbS9wYXQuY2VyIn0
   .
   eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6e
   yJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9ja2
   luZyI6ZmFsc2V9LCJwcml2YWN5dXJsIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9jb21
   taXRtZW50LXRvLXByaXZhY3kvIiwicW5hbWVtaW5pbWl6YXRpb24iOmZhbHNlfSwi
   c2VydmVyIjp7ImFkbiI6WyJleGFtcGxlLmNvbSJdfX0
   .
   4vQEAF_Vlp1Tr6sJmS4pnIKDRmIjH8EZzY5BMT2qJCHD8PmjBktWVnlmbmyHs05G
   KauRBdIFnfp3oDPbE0Jq4w

A.1.  X.509 Private Key in PKCS#8 Format for ES256 Example**

   -----BEGIN PRIVATE KEY-----
   MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgevZzL1gdAFr88hb2
   OF/2NxApJCzGCEDdfSp6VQO30hyhRANCAAQRWz+jn65BtOMvdyHKcvjBeBSDZH2r
   1RTwjmYSi9R/zpBnuQ4EiMnCqfMPWiZqB4QdbAd0E7oH50VpuZ1P087G
   -----END PRIVATE KEY-----

A.2.  X.509 Public Key for ES256 Example**

   -----BEGIN PUBLIC KEY-----
   MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEEVs/o5+uQbTjL3chynL4wXgUg2R9
   q9UU8I5mEovUf86QZ7kOBIjJwqnzD1omageEHWwHdBO6B+dFabmdT9POxg==
   -----END PUBLIC KEY-----

Appendix B.  Complete JWS JSON Serialization Representation with
             multiple Signatures

   The JWS payload used in this example as follows.

   {
     "server":{
         "adn":["example.com"]
     },
     "iat":1443208345,
     "exp":1443640345,
     "policyinfo": {
        "filtering": {
            "malwareblocking": true,
            "policyblocking": false
        },
        "qnameminimization":false,
        "privacyurl": "https://example.com/commitment-to-privacy/"
     }
   }




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   This would be serialized to the form (with line break used for
   display purposes only):

   {"exp":1443640345,"iat":1443208345,"policyinfo":{
   "filtering":{"malwareblocking": true,"policyblocking": false},
   "privacyurl":"https://example.com/commitment-to-privacy/",
   "qnameminimization":false},"server":{"adn":["example.com"]}}

   The JWS protected Header value used for the first signature is same
   as that used in the example in Appendix A.  The X.509 private key
   used for generating the first signature is same as that used in the
   example in Appendix A.1.

   The JWS Protected Header value used for the second signature is:

   {
     "alg":"ES384",
     "typ":"pat",
     "x5u":"https://cert.audit-example.com/pat.cer"
   }

   The complete JWS JSON Serialization for these values is as follows
   (with line breaks within values for display purposes only):

{
  "payload":
       "eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6
        eyJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9j
        a2luZyI6ZmFsc2V9LCJwcml2YWN5dXJsIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9j
        b21taXRtZW50LXRvLXByaXZhY3kvIiwicW5hbWVtaW5pbWl6YXRpb24iOmZhbHNl
        fSwic2VydmVyIjp7ImFkbiI6WyJleGFtcGxlLmNvbSJdfX0",
  "signatures":[
       {"protected":"eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHB
        zOi8vY2VydC5leGFtcGxlLmNvbS9wYXQuY2VyIn0",
        "signature": "4vQEAF_Vlp1Tr6sJmS4pnIKDRmIjH8EZzY5BMT2qJCHD8PmjBk
        tWVnlmbmyHs05GKauRBdIFnfp3oDPbE0Jq4w"},
       {"protected":"eyJhbGciOiJFUzM4NCIsInR5cCI6InBhdCIsIng1dSI6Imh0dHB
        zOi8vY2VydC5hdWRpdC1leGFtcGxlLmNvbS9wYXQuY2VyIn0",
        "signature":666ag_mAqDa3Oyxo1DGXUocr0MmRjpXwq8kWp1S21mvs2-kPCIq3
        0xsBJt4apy-sq3VyJgIqzjijoFYURhHvupF0obo-IFUGSZ1YHBCX_MiyBwJQJjtp
        S91ujDatRTtZ"}]
}

B.1.  X.509 Private Key in PKCS#8 format for E384 Example**







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   -----BEGIN PRIVATE KEY-----
   MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgevZzL1gdAFr88hb2
   OF/2NxApJCzGCEDdfSp6VQO30hyhRANCAAQRWz+jn65BtOMvdyHKcvjBeBSDZH2r
   1RTwjmYSi9R/zpBnuQ4EiMnCqfMPWiZqB4QdbAd0E7oH50VpuZ1P087G
   -----END PRIVATE KEY-----

B.2.  X.509 Public Key for ES384 Example**

   -----BEGIN PUBLIC KEY-----
   MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEEVs/o5+uQbTjL3chynL4wXgUg2R9
   q9UU8I5mEovUf86QZ7kOBIjJwqnzD1omageEHWwHdBO6B+dFabmdT9POxg==
   -----END PUBLIC KEY-----

Authors' Addresses

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

   Email: kondtir@gmail.com


   Dan Wing
   Citrix Systems, Inc.
   USA

   Email: dwing-ietf@fuggles.com


   Michael C. Richardson
   Sandelman Software Works
   USA

   Email: mcr+ietf@sandelman.ca


   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com







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