ADD WG                                                          T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                                 D. Wing
Expires: September 30, 2021                                       Citrix
                                                           M. Richardson
                                                Sandelman Software Works
                                                            M. Boucadair
                                                                  Orange
                                                          March 29, 2021


   DNS Server Selection: DNS Server Information with Assertion Token
               draft-reddy-add-server-policy-selection-08

Abstract

   The document defines a mechanism that is meant to communicate DNS
   resolver information to DNS clients for use as a criteria for server
   selection decisions.  Such an information that is cryptographically
   signed to attest its authenticity is used for the selection of DNS
   resolvers.  Typically, evaluating the resolver information and the
   signatory, DNS clients with minimal or no human intervention can
   select the DNS servers for resolving domain names.

   This assertion is useful for encrypted DNS (e.g., DNS-over-TLS, DNS-
   over-HTTPS, or DNS-over-QUIC) servers that are either public
   resolvers or 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 September 30, 2021.







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Copyright Notice

   Copyright (c) 2021 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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Resolver Assertion Token (REAT): Overview . . . . . . . . . .   4
   4.  REAT Header . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  'typ' (Type) Header Parameter . . . . . . . . . . . . . .   6
     4.2.  'alg' (Algorithm) Header Parameter  . . . . . . . . . . .   6
     4.3.  'x5u' (X.509 URL) Header Parameter  . . . . . . . . . . .   6
     4.4.  An Example of REAT Header . . . . . . . . . . . . . . . .   7
   5.  REAT Payload  . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  JWT Defined Claims  . . . . . . . . . . . . . . . . . . .   7
       5.1.1.  'iat' - Issued At Claim . . . . . . . . . . . . . . .   7
       5.1.2.  'exp' - Expiration Time Claim . . . . . . . . . . . .   7
     5.2.  REAT Specific Claims  . . . . . . . . . . . . . . . . . .   8
       5.2.1.  DNS Server Identity Claims  . . . . . . . . . . . . .   8
       5.2.2.  'resinfo' (Resolver Information) Claim  . . . . . . .   8
       5.2.3.  An Example  . . . . . . . . . . . . . . . . . . . . .   9
   6.  REAT Signature  . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Extending REAT  . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  Deterministic JSON Serialization  . . . . . . . . . . . . . .  10
     8.1.  Example REAT Deterministic JSON Form  . . . . . . . . . .  11
   9.  Using RESINFO Responses . . . . . . . . . . . . . . . . . . .  11
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Media Type Registration  . . . . . . . . . . . . . . . .  12
       11.1.1.  Media Type Registry Contents Additions Requested . .  12
     11.2.  JSON Web Token Claims Registration . . . . . . . . . . .  13
       11.2.1.  Registry Contents Additions Requested  . . . . . . .  13
     11.3.  DNS Resolver Information Registration  . . . . . . . . .  14
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  14
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  14



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     13.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  Example of ES256-based REAT JWS Serialization and
                Signature  . . . . . . . . . . . . . . . . . . . . .  17
     A.1.  X.509 Private Key in PKCS#8 Format for ES256 Example**  .  19
     A.2.  X.509 Public Key for ES256 Example**  . . . . . . . . . .  19
   Appendix B.  Complete JWS JSON Serialization Representation with
                multiple Signatures  . . . . . . . . . . . . . . . .  20
     B.1.  X.509 Private Key in PKCS#8 format for E384 Example** . .  21
     B.2.  X.509 Public Key for ES384 Example**  . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

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], DNS-over-TLS (DoT) [RFC7858], and DNS-over-QUIC (DoQ)
   [I-D.ietf-dprive-dnsoquic].

   DNS clients can discover and authenticate encrypted DNS servers
   provided by a local network, for example using the techniques
   proposed in [I-D.ietf-add-dnr] and [I-D.ietf-add-ddr].  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 if it is connecting to an encrypted DNS
   server hosted by a specific organization (e.g., ISP or Enterprise).
   This strengthens the protection as clients can detect and reject
   connections to encrypted DNS servers hosted by attackers.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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

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






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   The terms 'Evidence', 'Verifier', 'Background Check', 'Relying
   Party', 'Appraisal Policy', and 'Attestation Results' are defined in
   [I-D.ietf-rats-architecture].

3.  Resolver Assertion Token (REAT): Overview

   The mechanism used in this specification resembles the Background-
   Check Model discussed in Sections 5.2 and 5.3 of Remote attestation
   procedure (RATS) Architecture [I-D.ietf-rats-architecture].  RATS
   enables a relying party to establish a level of confidence in the
   trustworthiness of a remote peer through the creation of Evidence to
   assess the peer's trustworthiness, and an Appraisal Policy for such
   Evidence.

   In this document, the Relying Party is the DNS client and the
   Attester is the encrypted DNS server.  The Encrypted DNS servers MAY
   use "Domain Validation" (DV) certificates for certificate-based
   server authentication in TLS connections.

   The DNS server's resolver information needs to be validated and
   signed.  This signature is called an Attestation Result
   [I-D.ietf-rats-architecture].  This validation can be performed by
   the DNS operator itself (signed by the DNS operator's certificate)
   acting as a verifier or performed by an external Verifier (signed by
   that external Verifier).  The signing certificate can to be an
   Extended Validation (EV) certificate issued by a public CA in
   specific scenarios listed below.  An EV certificate is issued by the
   public CA after a thorough Background Check to verify the requesting
   organization's legal identity.  If the signing certificate is a EV
   certificate, it leaves the client with a better audit trail of the
   organization hosting the DNS server in comparison with the DV
   certificate.

   The use of EV certificate is needed in the following scenarios:

   o  It helps the client to avoid sending DNS queries to an Encrypted
      DNS server hosted by an attacker discovered insecurely (e.g.,
      using DHCP/RA or DNS).  For example, an attacker can get a domain
      name, domain-validated public certificate from a CA and host a
      Encrypted DNS server.  Furthermore, an attacker can use a public
      IP address, get an 'IP address'-validated public certificate from
      a CA and host a Encrypted DNS server.

   o  It can be used by the client to identify the Encrypted DNS server
      is hosted by a legal organization.

   The use of EV certificate is not required in the following scenarios:




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   o  If the Encrypted DNS server can only be discovered securely (e.g.,
      using IKEv2 [I-D.btw-add-ipsecme-ike]), the signing certificate
      need not be an EV certificate.

   o  Secure Zero Touch Provisioning [RFC8572] defines a bootstrapping
      strategy for enabling a networking device to securely obtain the
      required configuration information with no user input.  If the
      encrypted DNS server is insecurely discovered and not
      preconfigured in the networking device, the DNS client on the
      networking device can validate the Resolver Assertion Token
      signature using the owner certificate as per Section 3.2 of
      [RFC8572].

   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
   resolver information of the Encrypted DNS 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 resolver assertion
   token.

   The REsolver Assertion Token (REAT) specifically uses this token
   format and defines claims that convey the resolver information of
   Encrypted DNS server.

   The client can retrieve the REAT object using the RESINFO RRtype
   defined in [I-D.reddy-add-resolver-info] and QNAME of the domain name
   that is used to authenticate the DNS server (referred to as ADN in
   [RFC8310]).  If the special use domain name "resolver.arpa" defined
   in [I-D.ietf-add-ddr] is used to discover the Encrypted DNS server,
   the client can retrieve the REAT object using the RESINFO RRtype and
   QNAME of the special use domain name.

   The signature of REAT object MUST be validated by the DNS client.  If
   signature is invalid, the REAT object is rejected.  If signature is
   valid and signer is trusted, the DNS client can use that encrypted
   DNS server.







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4.  REAT Header

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

   The REAT header MUST include, at a minimum, the header parameters
   defined in Sections 4.1, 4.2, and 4.3.

4.1.  'typ' (Type) Header Parameter

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

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

4.2.  '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 REAT 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 REAT tokens may likewise be
   updated in the future.

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

4.3.  '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.





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4.4.  An Example of REAT Header

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

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

                      Figure 1: A REAT Header Example

5.  REAT Payload

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

   REAT 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].

5.1.  JWT Defined Claims

5.1.1.  '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].

5.1.2.  '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 REAT object should expire after a reasonable
   duration.  A short expiration time for the REAT object periodically
   reaffirms the resolver information of the DNS server to the DNS
   client and ensures the DNS client does not use outdated resolver



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   information.  If the DNS client knows the REAT object has expired, it
   should make another request to get the new REAT object from the DNS
   server.

5.2.  REAT Specific Claims

5.2.1.  DNS Server Identity Claims

   The DNS server identity is represented by a claim that is required
   for REAT: 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 REAT for further
   processing.

5.2.1.1.  '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.

5.2.1.2.  'uri' - URI Identity

   If the DNS server identity is of the form URI Template, as defined in
   [RFC6570], the claim name representing the identity MUST be 'uri' and
   the claim value is the URI Template form of the DNS server identity.

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

5.2.2.  'resinfo' (Resolver Information) Claim

   The 'resinfo' claim contains the resolver information of the DNS
   server defined in Section 5 of [I-D.reddy-add-resolver-info].






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5.2.3.  An Example

   Figure 2 shows an example of resolver information.

   {
     "server":{
         "adn":"example.com"
     },
     "iat":1443208345,
     "exp":1443640345,
     "resinfo": {
        "qnameminimization":false,
     }
   }

               Figure 2: An Example of Resolver Information

6.  REAT Signature

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

   For the JWS Payload and the JWS Protected Header, the lexicographic
   ordering and white space rules described in Section 4 and Section 5,
   and JSON serialization rules in Section 8 MUST be followed.

   The REAT 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 resolver information is attested using "Extended Validation" (EV)
   certificate 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 REAT 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 resolver information.

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





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   JWS JSON serialization (Step 7 in Section 5.1 of [RFC7515]) is
   supported for REAT to enable multiple signatures to be applied to the
   REAT object.  For example, the REAT 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 REAT Token.

7.  Extending REAT

   REAT includes the minimum set of claims needed to securely assert the
   resolver information of the DNS server.  JWT supports a mechanism to
   add additional asserted or signed information by simply adding new
   claims.  REAT 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 REAT object cannot
   assume that the DNS client will understand the new claims.

8.  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.





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

8.1.  Example REAT Deterministic JSON Form

   This section demonstrates the deterministic JSON serialization for
   the example REAT Payload shown in Section 5.2.3.

   The initial JSON object is shown in Figure 3.

   {
     "server":{
         "adn":"example.com"
     },
     "iat":1443208345,
     "exp":1443640345,
     "resinfo": {
        "qnameminimization":false,
     }
   }

                       Figure 3: Initial JSON Object

   The parent members of the JSON object are as follows, in
   lexicographic order: "exp", "iat", "resinfo", "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,
   "resinfo":{"qnameminimization":false},
   "server":{"adn":"example.com"}}

                     Figure 4: Deterministic JSON Form

9.  Using RESINFO Responses

   This document defines the following entry for the IANA DNS Resolver
   Information Registry that is defined in [I-D.reddy-add-resolver-
   info].

   o  The "attested-resinfo" name contains the full REAT object.  The
      REAT header, REAT payload, and REAT signature components comprise
      a full REAT object.  If the "attested-resinfo" name is conveyed to
      the client, the server need not convey the attributes
      "resinfourl", "identityurl", "extendeddnserror" and




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      "qnameminimization" attributes separately as that resolver
      information will be extracted by the client from the REAT payload.

10.  Security Considerations

   The use of REAT 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 resolver information of the DNS server being asserted.
   Bad actors can host encrypted DNS servers to invade the privacy of
   the user.  Bad actor can get a domain name, host encrypted DNS
   servers, and get the DNS server certificate signed by a CA.  The
   resolver information will have to be attested using EV certificates
   or a REAT object signer trusted by the DNS client to prevent the
   attack.

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

   If the REAT 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 DNS server can cause a disagreement
   between the auditor and the DNS server operation, hence the REAT
   object needs to be also asserted by the domain hosting the DNS
   server.  In addition, the REAT object needs to have a short
   expiration time (e.g., 7 days) to ensure the DNS server's domain re-
   asserts the resolver information and limits the damage from change in
   behaviour and mis-issuance.

11.  IANA Considerations

11.1.  Media Type Registration

11.1.1.  Media Type Registry Contents Additions Requested

   This section registers the 'application/rat' 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 REAT defined JWT.

   o  Type name: application

   o  Subtype name: rat

   o  Required parameters: n/a




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   o  Optional parameters: n/a

   o  Encoding considerations: 8bit; application/rat 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

   o  Published specification: [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

11.2.  JSON Web Token Claims Registration

11.2.1.  Registry Contents Additions Requested

   IANA is requested to assign the following claims in the registry
   maintained in: https://www.iana.org/assignments/jwt/jwt.xhtml.

   o  Claim Name: 'server'

   o  Claim Description: DNS server identity

   o  Change Controller: IESG




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   o  Specification Document(s): Section 5.2.1 of [THIS_DOCUMENT]

   o  Claim Name: 'resinfo'

   o  Claim Description: Resolver information of DNS server.

   o  Change Controller: IESG

   o  Specification Document(s): Section 5.2.2 of [THIS_DOCUMENT]

11.3.  DNS Resolver Information Registration

   IANA will add the name "attested-resinfo" to the DNS Resolver
   Information registry defined in Section 7.2 of [I-D.reddy-add-
   resolver-info].

12.  Acknowledgments

   This specification leverages some of the work that has been done in
   [RFC8225].  Thanks to Tommy Jensen, Ted Lemon, Paul Wouters, Neil
   Cook, Vittorio Bertola, Vinny Parla, Chris Box, Ben Schwartz and
   Shashank Jain for the discussion and comments.

13.  References

13.1.  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>.




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

   [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>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [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>.




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   [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>.

13.2.  Informative References

   [I-D.btw-add-home]
              Boucadair, M., Reddy.K, T., Wing, D., Cook, N., and T.
              Jensen, "DHCP and Router Advertisement Options for
              Encrypted DNS Discovery", draft-btw-add-home-12 (work in
              progress), January 2021.

   [I-D.btw-add-ipsecme-ike]
              Boucadair, M., Reddy.K, T., Wing, D., and V. Smyslov,
              "Internet Key Exchange Protocol Version 2 (IKEv2)
              Configuration for Encrypted DNS", draft-btw-add-ipsecme-
              ike-01 (work in progress), September 2020.

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

   [I-D.ietf-dprive-dnsoquic]
              Huitema, C., Mankin, A., and S. Dickinson, "Specification
              of DNS over Dedicated QUIC Connections", draft-ietf-
              dprive-dnsoquic-01 (work in progress), October 2020.

   [I-D.ietf-rats-architecture]
              Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
              W. Pan, "Remote Attestation Procedures Architecture",
              draft-ietf-rats-architecture-08 (work in progress),
              December 2020.

   [I-D.pp-add-resinfo]
              Sood, P. and P. Hoffman, "DNS Resolver Information Self-
              publication", draft-pp-add-resinfo-02 (work in progress),
              June 2020.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

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





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   [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>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [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>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/info/rfc8914>.

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

Appendix A.  Example of ES256-based REAT JWS Serialization and Signature

   For REAT, 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 REAT.

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




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   {
     "server":{
         "adn":"example.com"
     },
     "iat":1443208345,
     "exp":1443640345,
     "resinfo": {
        "qnameminimization":false
     }
   }

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

   {"exp":1443640345,"iat":1443208345,"resinfo":{
   "qnameminimization":false},"server":{"adn":"example.com"}}

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

   eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicmVzaW5mbyI6ey
   JxbmFtZW1pbmltaXphdGlvbiI6ZmFsc2V9LCJzZXJ2ZXIiOnsiYWRuIjoiZXhh
   bXBsZS5jb20ifX0



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

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

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

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

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







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   eyJhbGciOiJFUzI1NiIsInR5cCI6InJhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
   eGFtcGxlLmNvbS9yYXQuY2VyIn0



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


   d1g7szj0roHsWe8psCzYVl4QdN2b7pQnq8EJhc4j3GOJj2NE6M9Em6aidtycnFJ5
   mRj3ojiUfVF6rK5RksD0rg



   Step 8 describes how to create the final REAT 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):

   eyJhbGciOiJFUzI1NiIsInR5cCI6InJhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
   eGFtcGxlLmNvbS9yYXQuY2VyIn0
   .

   eyJhbGciOiJFUzI1NiIsInR5cCI6InJhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
   eGFtcGxlLmNvbS9yYXQuY2VyIn0
   .
   d1g7szj0roHsWe8psCzYVl4QdN2b7pQnq8EJhc4j3GOJj2NE6M9Em6aidtycnFJ5
   mRj3ojiUfVF6rK5RksD0rg


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-----




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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,
     "resinfo": {
        "qnameminimization":false
     }
   }

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

   {"exp":1443640345,"iat":1443208345,"resinfo":{
   "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":"rat",
     "x5u":"https://cert.audit-example.com/rat.cer"
   }

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














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{
  "payload":
       "eyJhbGciOiJFUzI1NiIsInR5cCI6InJhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
        eGFtcGxlLmNvbS9yYXQuY2VyIn0",
  "signatures":[
       {"protected":"eyJhbGciOiJFUzI1NiIsInR5cCI6InJhdCIsIng1dSI6Imh0dHBz
        Oi8vY2VydC5leGFtcGxlLmNvbS9yYXQuY2VyIn0",
        "signature":"d1g7szj0roHsWe8psCzYVl4QdN2b7pQnq8EJhc4j3GOJj2NE6M9E
        m6aidtycnFJ5mRj3ojiUfVF6rK5RksD0rg"},
       {"protected":"eyJhbGciOiJFUzM4NCIsInR5cCI6InJhdCIsIng1dSI6Imh0dHB
        zOi8vY2VydC5hdWRpdC1leGFtcGxlLmNvbS9yYXQuY2VyIn0",
        "signature":"GnKuEEFql_Y8HdZl_mqd027DlziGRXFHvjMoY_ukX-M0k5v2jSL
        vsQAYOGdKFnt3JY6t938HfBV1onsWerNhgceMJpx5hAsl-xus3fmNY8K1g6QK39
        hn2Dhbleeeyp0f"}]
}

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

   -----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




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   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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