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draft-add-server-selection-information-03.txt
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ADD WG T. Reddy
Internet-Draft McAfee
Intended status: Standards Track D. Wing
Expires: December 17, 2020 Citrix
M. Richardson
Sandelman Software Works
M. Boucadair
Orange
June 15, 2020
DNS Server Selection: DNS Server Information with Assertion Token
draft-reddy-add-server-policy-selection-03
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 December 17, 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 . . . . . . . . . . . 6
5. PAT Header . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. 'typ' (Type) Header Parameter . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . . . 9
6.2.1. DNS Server Identity Claims . . . . . . . . . . . . . 9
6.2.2. 'policyinfo' (Policy Information) Claim . . . . . . . 9
6.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 11
7. PAT Signature . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Extending PAT . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Deterministic JSON Serialization . . . . . . . . . . . . . . 12
9.1. Example PAT Deterministic JSON Form . . . . . . . . . . . 13
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
11. Security Considerations . . . . . . . . . . . . . . . . . . . 14
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12.1. Media Type Registration . . . . . . . . . . . . . . . . 15
12.1.1. Media Type Registry Contents Additions Requested . . 15
12.2. JSON Web Token Claims Registration . . . . . . . . . . . 16
12.2.1. Registry Contents Additions Requested . . . . . . . 16
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 . . . . . . . . . . . . . . . . . 18
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** . . . . . . . . . . 22
Appendix B. Complete JWS JSON Serialization Representation with
multiple Signatures . . . . . . . . . . . . . . . . 22
B.1. X.509 Private Key in PKCS#8 format for E384 Example** . . 23
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.
Phishing blocking: Indicates whether the DNS server offers phishing
blocking service.
Policy blocking: Indicates whether the DNS server maintains a block-
list due to an policy by the operator of the DNS server.
Censored blocking: Indicates whether the DNS server maintains a
block-list based on a requirement from an external entity.
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
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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.
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).
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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
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.
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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.
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.
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{
"typ":"pat",
"alg":"ES256",
"x5u":"https://cert.example.com/pat.cer"
}
Figure 1: A PAT Header Example
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
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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
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 or failure codes are returned based on policy criteria,
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such as to prevent access to malware sites or objectionable
content (e.g., legal obligation). This optional attribute has the
following structure:
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.
phishingblocking: The DNS server offers phishing blocking
service. If access to phishing domains is blocked, the
parameter value is set to 'true'.
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
[I-D.ietf-dnsop-extended-error] identifies access to domains is
blocked due to an policy by the operator of the DNS server.
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 [I-D.ietf-dnsop-extended-error]
identifies access to domains is blocked based on a requirement
from an external entity.
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.
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.
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.
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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.
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.
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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.
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.
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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
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
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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
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.
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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
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, [email protected]
o Intended usage: COMMON
o Restrictions on usage: none
o Author: Tirumaleswar Reddy, [email protected]
o Change Controller: IESG
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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]
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, Vittorio
Bertola 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>.
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[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>.
[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>.
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[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.
[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>.