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draft-add-server-selection-information-03.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-reddy-add-server-policy-selection-03"
ipr="trust200902">
<front>
<title abbrev="DNS Server Info with Assertion Token">DNS Server Selection:
DNS Server Information with Assertion Token</title>
<author fullname="Tirumaleswar Reddy" initials="T." surname="Reddy">
<organization abbrev="McAfee">McAfee, Inc.</organization>
<address>
<postal>
<street>Embassy Golf Link Business Park</street>
<city>Bangalore</city>
<region>Karnataka</region>
<code>560071</code>
<country>India</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Dan Wing" initials="D." surname="Wing">
<organization abbrev="Citrix">Citrix Systems, Inc.</organization>
<address>
<postal>
<street></street>
<country>USA</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Michael C. Richardson" initials="M."
surname="Richardson">
<organization>Sandelman Software Works</organization>
<address>
<postal>
<street></street>
<country>USA</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Mohamed Boucadair" initials="M." surname="Boucadair">
<organization>Orange</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<code>35000</code>
<country>France</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<date />
<workgroup>ADD WG</workgroup>
<abstract>
<t>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.</t>
<t>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.</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t><xref target="RFC7626"></xref> discusses DNS privacy considerations
in both "on the wire" (Section 2.4 of <xref target="RFC7626"></xref>)
and "in the server" (Section 2.5 of <xref target="RFC7626"></xref>)
contexts. Examples of protocols that provide encrypted channels between
DNS clients and servers are DNS-over-HTTPS (DoH) <xref
target="RFC8484"></xref> and DNS-over-TLS (DoT) <xref
target="RFC7858"></xref>.</t>
<t>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 <xref target="I-D.btw-add-home"></xref>. 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).</t>
<t>The DNS Recursive Operator Privacy (DROP) statement explained in
<xref target="I-D.ietf-dprive-bcp-op"></xref> 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.</t>
<t>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.</t>
<t>This document also defines a mechanism for DNS clients to gather a
set of information related to discovered (or pre-configured) servers and
use that information to feed a DNS server selection procedure. The
following parameters are supported in this version:<list style="hanging">
<t hangText="Malware blocking:">Indicates whether the DNS server
offers malware blocking service.</t>
<t hangText="Phishing blocking:">Indicates whether the DNS server
offers phishing blocking service.</t>
<t hangText="Policy blocking:">Indicates whether the DNS server
maintains a block-list due to a policy by the operator of the DNS
server.</t>
<t hangText="Censored blocking:">Indicates whether the DNS server
maintains a block-list based on a requirement from an external
entity. This version of the specification does not distinguish blocking from regulatory bodies (e.g., LEA) vs. arbitrary blocking. Such differentiation may be defined if required. </t>
<t hangText="QNAME minimization:">Indicates whether the DNS server
implements QNAME minimisation <xref target="RFC7816"></xref>.</t>
</list></t>
<t>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.</t>
</section>
<section anchor="scope" title="Sample Use Cases ">
<t>The mechanism for a DNS server to communicate its cryptographically
signed policies to DNS clients contributes to solve the following
problems in various deployments:<list style="symbols">
<t>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).</t>
<t>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.</t>
<t>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.</t>
<t>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 <xref
target="I-D.ietf-dnsop-extended-error"></xref>, the DNS client can
securely identify access to the domain is censored by the
network.</t>
<t>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 <xref
target="I-D.ietf-dnssd-push"></xref> 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 <xref
target="exp-header-parameter"></xref> to identify policy
updates.</t>
</list></t>
</section>
<section anchor="notation" title="Terminology">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP 14
<xref target="RFC2119"></xref><xref target="RFC8174"></xref> when, and
only when, they appear in all capitals, as shown here.</t>
<t>This document makes use of the terms defined in <xref
target="RFC8499"></xref> and <xref
target="I-D.ietf-dnsop-terminology-ter"></xref>.</t>
<t>'DoH/DoT' refers to DNS-over-HTTPS and/or DNS-over-TLS.</t>
<t>'Encrypted DNS' refers to a DNS protocol that provides an encrypted
channel between a DNS client and server (e.g., DoT or DoH).</t>
</section>
<section anchor="PAT" title="Policy Assertion Token (PAT): Overview">
<t>JSON Web Token (JWT) <xref target="RFC7519"></xref> and JSON Web
Signature (JWS) <xref target="RFC7515"></xref> 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 policy information
of the DoH/DoT server. Additionally, JWS provides a path for updating
methods and cryptographic algorithms used for the associated digital
signatures.</t>
<t>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.</t>
<t>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 <xref target="I-D.pp-add-resinfo"></xref>. 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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section anchor="pat_header" title="PAT Header">
<t>The JWS token header is a JOSE header (Section 4 of <xref
target="RFC7515"></xref>) that defines the type and encryption algorithm
used in the token.</t>
<t>PAT header MUST include, at a minimum, the header parameters defined
in Sections <xref format="counter"
target="typ-type-header-parameter"></xref>, <xref format="counter"
target="alg-algorithm-header-parameter"></xref>, and <xref
format="counter" target="x5u-x509-url-header-parameter"></xref>.</t>
<section anchor="typ-type-header-parameter"
title="'typ' (Type) Header Parameter">
<t>The 'typ' (Type) Header Parameter is defined Section 4.1.9 of <xref
target="RFC7515"></xref> to declare the media type of the complete
JWS.</t>
<t>For PAT Token the 'typ' header MUST be the string 'pat'. This
represents that the encoded token is a JWT of type pat.</t>
</section>
<section anchor="alg-algorithm-header-parameter"
title="'alg' (Algorithm) Header Parameter">
<t>The 'alg' (Algorithm) Header Parameter is defined in Section 4.1.1
of <xref target="RFC7515"></xref>. 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)
<xref target="RFC7518"></xref> Section 3.1.</t>
<t>For the creation and verification of PAT tokens and their digital
signatures, implementations MUST support ES256 as defined in Section
3.4 of <xref target="RFC7518"></xref>. Implementations MAY support
other algorithms registered in the JSON Web Signature and Encryption
Algorithms registry created by <xref target="RFC7518"></xref>. 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.</t>
<t>Implementations of PAT digital signatures using ES256 as defined
above SHOULD use deterministic ECDSA when supported for the reasons
stated in <xref target="RFC6979"></xref>.</t>
</section>
<section anchor="x5u-x509-url-header-parameter"
title="'x5u' (X.509 URL) Header Parameter">
<t>As defined in Section 4.1.5 of <xref target="RFC7515"></xref>, the
'x5u' header parameter defines a URI <xref target="RFC3986"></xref>
referring to the resource for the X.509 public key certificate or
certificate chain <xref target="RFC5280"></xref> corresponding to the
key used to digitally sign the JWS. Generally, as defined in Section
4.1.5 of <xref target="RFC7515"></xref> this corresponds to an HTTPS
or DNSSEC resource using integrity protection.</t>
</section>
<section anchor="example-pat-header" title="An Example of PAT Header">
<t>An example of the PAT header is shown in <xref target="ex"></xref>.
It includes the specified PAT type, ES256 algorithm, and an URI
referencing the network location of the certificate needed to validate
the PAT signature.</t>
<figure align="center" anchor="ex" title="A PAT Header Example">
<artwork><![CDATA[{
"typ":"pat",
"alg":"ES256",
"x5u":"https://cert.example.com/pat.cer"
}
]]></artwork>
</figure>
</section>
</section>
<section anchor="pat_payload" title="PAT Payload">
<t>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 <xref target="RFC7519"></xref>)
and are encoded as defined by the JWS Payload (Section 3 of <xref
target="RFC7515"></xref>).</t>
<t>PAT defines the use of a standard JWT-defined claim as well as custom
claims corresponding to the DoT or DoH servers.</t>
<t>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 <xref
target="RFC7519"></xref>.</t>
<section anchor="jwt-defined-claims" title="JWT Defined Claims">
<section anchor="iat-issued-at-claim" title="'iat' - Issued At Claim">
<t>The JSON claim MUST include the 'iat' (Section 4.1.6 of <xref
target="RFC7519"></xref>) 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
<xref target="RFC7519"></xref>.</t>
</section>
<section anchor="exp-header-parameter"
title="'exp' - Expiration Time Claim">
<t>The JSON claim MUST include the 'exp' (Section 4.1.4 of <xref
target="RFC7519"></xref>) 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.</t>
</section>
</section>
<section anchor="pat_claims" title="PAT Specific Claims">
<section anchor="server-identity" title="DNS Server Identity Claims">
<t>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.</t>
<t>These identities can be represented as either authentication
domain name (ADN) (defined in <xref target="RFC8310"></xref>) or
Uniform Resource Indicators (URI).</t>
<t>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.</t>
<section anchor="adn"
title="'adn' - Authentication Domain Name Identity">
<t>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.</t>
</section>
<section anchor="uri-identity" title="'uri' - URI Identity">
<t>If the DNS server identity is of the form URI, as defined in
<xref target="RFC3986"></xref>, the claim name representing the
identity MUST be 'uri' and the claim value is the URI form of the
DNS server identity.</t>
<t>As a reminder, if DoH is supported by the DNS server, the DNS
client uses the https URI scheme (Section 3 of <xref
target="RFC8484"></xref>).</t>
</section>
</section>
<section anchor="policyinfo"
title="'policyinfo' (Policy Information) Claim">
<t>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:</t>
<t><list style="hanging">
<t hangText="filtering:">If the DNS server changes some of the
answers that it returns or failure codes are returned based on
policy criteria, such as to prevent access to malware sites or
objectionable content (e.g., legal obligation). This optional
attribute has the following structure:<list style="hanging">
<t hangText="malwareblocking:">The DNS server offers malware
blocking service. If access to domains is blocked on threat
data, the parameter value is set to 'true'. Note that some
of the commonly known types of malware are viruses, worms,
trojans, bots, ransomware, backdoors, spyware, and adware.
</t>
<t hangText="phishingblocking:">The DNS server offers
phishing blocking service. If access to phishing domains is
blocked, the parameter value is set to 'true'.</t>
<t hangText="policyblocking:">If access to domains is
blocked due to an internal policy imposed by the operator of
the DNS server, the parameter value is set to 'true'. Note
that the extended error code "Blocking" defined in Section
4.16 of <xref target="I-D.ietf-dnsop-extended-error"></xref>
identifies access to domains is blocked due to an policy by
the operator of the DNS server.</t>
<t hangText="censoredblocking:">If access to domains is
blocked due to an external requirement imposed by an
external entity (e.g., Law Enforcement Agency) for legal
reasons, the parameter value is set to 'true'. Note that the
extended error code "Censored" defined in Section 4.17 of
<xref target="I-D.ietf-dnsop-extended-error"></xref>
identifies access to domains is blocked based on a
requirement from an external entity.</t>
</list></t>
<t hangText="qnameminimization:">If the DNS server implements
QNAME minimisation <xref target="RFC7816"></xref> 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.</t>
<t hangText="clientauth:">If the DNS server policy requires
client authentication, the parameter value is set to true. For
example, when not on the enterprise network (e.g., at home or
coffeeshop) yet needing to access the enterprise DoH/DoT server
but not through a tunnel, roaming users can use client
authentication to access the Enterprise provided DoH/DoT server.
This is a optional attribute.</t>
<t hangText="privacyurl:">A URL that points to the privacy
policy information of the DNS server. This is a mandatory
attribute.</t>
<t hangText="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.</t>
</list></t>
</section>
<section anchor="pat_payload_example" title="Example">
<t><xref target="poex"></xref> shows an example of policy
information.</t>
<figure anchor="poex" title="An Example of Policy Information">
<artwork><![CDATA[{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"filtering": {
"malwareblocking": true,
"policyblocking": false
},
"qnameminimization":false,
"privacyurl": "https://example.com/commitment-to-privacy/"
}
}
]]></artwork>
</figure>
</section>
</section>
</section>
<section anchor="pat_signature" title="PAT Signature">
<t>The signature of the PAT is created as specified in Section 5.1 of
<xref target="RFC7515"></xref> (Steps 1 through 6). PAT MUST use the JWS
Protected Header.</t>
<t>For the JWS Payload and the JWS Protected Header, the lexicographic
ordering and white space rules described in <xref
target="pat_header"></xref> and <xref target="pat_payload"></xref>, and
JSON serialization rules in <xref target="json_serialization"></xref>
MUST be followed.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t><xref
target="example-es256-based-pat-jws-serialization-and-signature"></xref>
provides an example of how to follow the steps to create the JWS
Signature.</t>
<t>JWS JSON serialization (Step 7 in Section 5.1 of <xref
target="RFC7515"></xref>) 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.</t>
<t><xref
target="example-es256-based-pat-jws-serialization-and-signatures"></xref>
includes an example of the full JWS JSON serialization representation
with multiple signatures.</t>
<t>Section 5.1 of <xref target="RFC7515"></xref> (Step 8) describes the
method to create the final JWS Compact Serialization form of the PAT
Token.</t>
</section>
<section anchor="extending_pat" title="Extending PAT">
<t>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 (<xref
target="RFC7519">Section 10.1 of </xref>). 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.</t>
</section>
<section anchor="json_serialization"
title="Deterministic JSON Serialization">
<t>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.</t>
<t>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 <xref target="RFC7638"></xref> (Step 1).</t>
<t><list style="numbers">
<t>The JSON object MUST contain no whitespace or line breaks before
or after any syntactic elements.</t>
<t>JSON objects MUST have the keys ordered lexicographically by the
Unicode <xref target="UNICODE"></xref> code points of the member
names.</t>
<t>JSON value literals MUST be lowercase.</t>
<t>JSON numbers are to be encoded as integers unless the field is
defined to be encoded otherwise.</t>
<t>Encoding rules MUST be applied recursively to member values and
array values.</t>
</list></t>
<section anchor="example-pat-deterministic-json-form"
title="Example PAT Deterministic JSON Form">
<t>This section demonstrates the deterministic JSON serialization for
the example PAT Payload shown in <xref
target="pat_payload_example"></xref>.</t>
<t>The initial JSON object is shown in <xref
target="initial"></xref>.</t>
<figure anchor="initial" title="Initial JSON Object">
<artwork><![CDATA[{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"qnameminimization":false,
"privacyurl": "https://example.com/commitment-to-privacy/"
}
}
]]></artwork>
</figure>
<t>The parent members of the JSON object are as follows, in
lexicographic order: "exp", "iat", "policyinfo", "server".</t>
<t>The final constructed deterministic JSON serialization
representation, with whitespace and line breaks removed, (with line
breaks used for display purposes only) is:</t>
<figure anchor="final" title="Deterministic JSON Form">
<artwork><![CDATA[{"exp":1443640345,"iat":1443208345,
"policyinfo":{"privacyurl":"https://example.com/commitment-to-privacy/",
"qnameminimization":false},"server":{"adn":["example.com"]}}
]]></artwork>
</figure>
</section>
</section>
<section anchor="privacy" title="Privacy Considerations">
<t>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.</t>
<t>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.</t>
<t>Another scenario is bootstrapping a networking device to use the
encrypted DNS server in the local network. Secure Zero Touch
Provisioning <xref target="RFC8572"></xref> 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 <xref
target="RFC8572"></xref>.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>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 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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<section anchor="media-type-registration"
title="Media Type Registration">
<section anchor="media-type-registry-contents-additions-requested"
title="Media Type Registry Contents Additions Requested">
<t>This section registers the 'application/pat' media type <xref
target="RFC2046"></xref> in the 'Media Types' registry in the manner
described in <xref target="RFC6838"></xref>, which can be used to
indicate that the content is a PAT defined JWT.</t>
<t><list style="symbols">
<t>Type name: application</t>
<t>Subtype name: pat</t>
<t>Required parameters: n/a</t>
<t>Optional parameters: n/a</t>
<t>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..</t>
<t>Security considerations: See the Security Considerations
Section of <xref target="RFC7515"></xref>.</t>
<t>Interoperability considerations: n/a</t>
<t>Published specification: [TODO this document]</t>
<t>Applications that use this media type: DNS</t>
<t>Fragment identifier considerations: n/a</t>
<t>Additional information: <vspace blankLines="1" /> Magic
number(s): n/a File extension(s): n/a Macintosh file type
code(s): n/a</t>
<t>Person & email address to contact for further
information: Tirumaleswar Reddy, [email protected]</t>
<t>Intended usage: COMMON</t>
<t>Restrictions on usage: none</t>
<t>Author: Tirumaleswar Reddy, [email protected]</t>
<t>Change Controller: IESG</t>
<t>Provisional registration? No</t>
</list></t>
</section>
</section>
<section anchor="json-web-token-claims-registration"
title="JSON Web Token Claims Registration">
<section anchor="registry-contents-additions-requested"
title="Registry Contents Additions Requested">
<t><list style="symbols">
<t>Claim Name: 'server'</t>
<t>Claim Description: DNS server identity</t>
<t>Change Controller: IESG</t>
<t>Specification Document(s): <xref
target="server-identity"></xref> of [TODO this document]</t>
<t>Claim Name: 'policyinfo'</t>
<t>Claim Description: Policy information of DNS server.</t>
<t>Change Controller: IESG</t>
<t>Specification Document(s): <xref target="policyinfo"></xref>
of [TODO this document]</t>
</list></t>
</section>
</section>
<section anchor="resolver-information"
title="DNS Resolver Information Registration">
<t>IANA will add the names filtering, qnameminimization, privacyurl
and auditurl to the DNS Resolver Information registry defined in
Section 4.2 of <xref target="I-D.pp-add-resinfo"></xref>.</t>
</section>
</section>
<section anchor="acknowledgments" title="Acknowledgments">
<t>This specification leverages some of the work that has been done in
<xref target="RFC8225"></xref>. Thanks to Ted Lemon, Paul Wouters, Neil
Cook, Vittorio Bertola and Shashank Jain for the discussion and
comments.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include='reference.RFC.8174'?>
<?rfc include="reference.RFC.8484"?>
<?rfc include="reference.RFC.8499"?>
<?rfc include="reference.RFC.5280"?>
<?rfc include="reference.RFC.7515"?>
<?rfc include="reference.RFC.7519"?>
<?rfc include="reference.RFC.7518"?>
<?rfc include="reference.RFC.6979"?>
<?rfc include="reference.RFC.3986"?>
<?rfc include="reference.RFC.7638"?>
<?rfc include="reference.RFC.6838"?>
<?rfc include="reference.RFC.2046"?>
<?rfc include="reference.RFC.7858"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.8310"?>
<?rfc include='reference.I-D.pp-add-resinfo'?>
<?rfc include='reference.I-D.ietf-dnssd-push'?>
<?rfc include="reference.RFC.7626"?>
<?rfc include="reference.RFC.7816"?>
<?rfc include="reference.RFC.8225"?>
<?rfc include="reference.RFC.8572"?>
<?rfc include='reference.I-D.btw-add-home'?>
<?rfc include='reference.I-D.ietf-dnsop-extended-error' ?>
<?rfc include='reference.I-D.ietf-dnsop-terminology-ter'?>
<?rfc include='reference.I-D.ietf-dprive-bcp-op'?>
<reference anchor="UNICODE"
target="http://www.unicode.org/versions/latest/">
<front>
<title>The Unicode Standard</title>
<author>
<organization>The Unicode Consortium</organization>
</author>
<date day="21" month="June" year="2016" />
</front>
</reference>
</references>
<section anchor="example-es256-based-pat-jws-serialization-and-signature"
title="Example ES256 based PAT JWS Serialization and Signature">
<t>For PAT, there will always be a JWS with the following members:</t>
<t><list style="symbols">
<t>'protected', with the value BASE64URL(UTF8(JWS Protected
Header))</t>
<t>'payload', with the value BASE64URL (JWS Payload)</t>
<t>'signature', with the value BASE64URL(JWS Signature)</t>
</list></t>
<t>This example will follow the steps in JWS <xref
target="RFC7515"></xref> Section 5.1, steps 1-6 and 8 and incorporates
the additional serialization steps required for PAT.</t>
<t>Step 1 for JWS references the JWS Payload, an example PAT Payload is
as follows:</t>
<figure>
<artwork><![CDATA[{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"policyinfo": {
"filtering": {
"malwareblocking": true,
"policyblocking": false
},
"qnameminimization":false,
"privacyurl": "https://example.com/commitment-to-privacy/"
}
}
]]></artwork>
</figure>
<t>This would be serialized to the form (with line break used for
display purposes only):</t>
<figure>
<artwork><![CDATA[{"exp":1443640345,"iat":1443208345,"policyinfo":{
"filtering":{"malwareblocking": true,"policyblocking": false},
"privacyurl":"https://example.com/commitment-to-privacy/",
"qnameminimization":false},"server":{"adn":["example.com"]}}
]]></artwork>
</figure>
<t>Step 2 Computes the BASE64URL(JWS Payload) producing this value (with
line break used for display purposes only):</t>
<figure>
<artwork><![CDATA[
eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicG9saWN5aW5mbyI6e
yJmaWx0ZXJpbmciOnsibWFsd2FyZWJsb2NraW5nIjp0cnVlLCJwb2xpY3libG9ja2
luZyI6ZmFsc2V9LCJwcml2YWN5dXJsIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9jb21
taXRtZW50LXRvLXByaXZhY3kvIiwicW5hbWVtaW5pbWl6YXRpb24iOmZhbHNlfSwi
c2VydmVyIjp7ImFkbiI6WyJleGFtcGxlLmNvbSJdfX0
]]></artwork>
</figure>
<t>For Step 3, an example PAT Protected Header comprising the JOSE
Header is as follows:</t>
<figure>
<artwork><![CDATA[
{
"alg":"ES256",
"typ":"pat",
"x5u":"https://cert.example.com/pat.cer"
}
]]></artwork>
</figure>
<t>This would be serialized to the form (with line break used for
display purposes only):</t>
<figure>
<artwork><![CDATA[
{"alg":"ES256","typ":"pat","x5u":"https://cert.example.com
/pat.cer"}
]]></artwork>
</figure>
<t>Step 4 Performs the BASE64URL(UTF8(JWS Protected Header)) operation
and encoding produces this value (with line break used for display
purposes only):</t>
<figure>
<artwork><![CDATA[
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
eGFtcGxlLmNvbS9wYXQuY2VyIn0
]]></artwork>
</figure>
<t>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).</t>
<figure>
<artwork><![CDATA[
4vQEAF_Vlp1Tr6sJmS4pnIKDRmIjH8EZzY5BMT2qJCHD8PmjBktWVnlmbmyHs05G
KauRBdIFnfp3oDPbE0Jq4w
]]></artwork>
</figure>
<t>Step 8 describes how to create the final PAT token, concatenating the
values in the order Header.Payload.Signature with period