DPRIVE WG T. Reddy
Internet-Draft McAfee
Intended status: Standards Track D. Wing
Expires: April 5, 2020 Citrix
M. Richardson
Sandelman Software Works
October 3, 2019
DNS server privacy policy with assertion token
draft-reddy-dprive-dprive-privacy-policy-00
Abstract
Users want to control how their DNS queries are handled by DNS
servers so they can configure their system to use DNS servers that
comply with their privacy expectations.
This document defines a mechanism for a DNS server to communicate its
privacy policy to a DNS client. This communication is
cryptographically signed to attest to its authenticity. By
evaluating the DNS privacy policy and the signatory, the DNS client
can choose a DNS server that best supports its desired privacy
policies. The privacy assertion token is particularly useful for
DNS-over-TLS and DNS-over-HTTPS servers, both public resolvers and
those discovered on the 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 April 5, 2020.
Reddy, et al. Expires April 5, 2020 [Page 1]
Internet-Draft Asserted DNS server privacy policy October 2019
Copyright Notice
Copyright (c) 2019 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Privacy assertion token (PAT) overview . . . . . . . . . . . 4
4. PAT Header . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. "typ" (Type) Header Parameter . . . . . . . . . . . . . . 5
4.2. "alg" (Algorithm) Header Parameter . . . . . . . . . . . 5
4.3. "x5u" (X.509 URL) Header Parameter . . . . . . . . . . . 6
4.4. Example PAT header . . . . . . . . . . . . . . . . . . . 6
5. PAT Payload . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. JWT defined claims . . . . . . . . . . . . . . . . . . . 7
5.1.1. "iat" - Issued At claim . . . . . . . . . . . . . . . 7
5.1.2. "exp" - Expiration Time claim . . . . . . . . . . . . 7
5.2. PAT specific claims . . . . . . . . . . . . . . . . . . . 7
5.2.1. DNS server Identity Claims . . . . . . . . . . . . . 7
5.2.2. "privinfo" (Privacy Information) Claim . . . . . . . 8
5.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 10
6. PAT Signature . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Extending PAT . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Deterministic JSON Serialization . . . . . . . . . . . . . . 12
8.1. Example PAT deterministic JSON form . . . . . . . . . . . 13
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11.1. Media Type Registration . . . . . . . . . . . . . . . . 15
11.1.1. Media Type Registry Contents Additions Requested . . 15
11.2. JSON Web Token Claims Registration . . . . . . . . . . . 16
11.2.1. Registry Contents Additions Requested . . . . . . . 16
11.3. DNS Resolver Information Registration . . . . . . . . . 16
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
13.1. Normative References . . . . . . . . . . . . . . . . . . 16
Reddy, et al. Expires April 5, 2020 [Page 2]
Internet-Draft Asserted DNS server privacy policy October 2019
13.2. 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** . . . . . . . . . . 21
Appendix B. Complete JWS JSON Serialization Representation with
multiple Signatures . . . . . . . . . . . . . . . . 21
B.1. X.509 Private Key in PKCS#8 format for E384 Example** . . 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. In recent years there has also been an increase
in the availability of "public resolvers"
[I-D.ietf-dnsop-terminology-bis] which DNS clients may be pre-
configured to use instead of the default network resolver because
they offer a specific feature (e.g., good reachability, encrypted
transport, strong privacy policy, filtering (or lack of), etc.).
While a human can read the privacy policy of a DNS server operator,
this information is not machine-parsable to allow automatic DNS
server selection by the DNS client software. For DNS servers
operated on the local network, the DNS client can be securely
bootstrapped to discover and authenticate DNS-over-TLS and DNS-over-
HTTPS servers provided by a local network using the technique
proposed in [I-D.reddy-dprive-bootstrap-dns-server]. By creating a
machine-parsable DNS server privacy policy, the DNS client can
automatically allow using a DNS server on the local network that
complies with the DNS client's privacy policy.
This document defines a method for creating and validating a token
that cryptographically verifies the privacy policy information of a
DNS server, such as a DNS-over-TLS or DNS-over-HTTPS server.
The cryptographically signed privacy statement allows a DNS client to
connect to multiple DNS servers and select the DNS server that
adheres to the privacy preserving data policy requirements of the
client. For example, a browser with pre-configured DNS-over-HTTPS
server can discover the DNS-over-HTTPS server provided the local
network, connects to both the DNS servers, gets the privacy policy
information from each of the DNS servers, validates the signatures
and uses a server that meets the privacy preserving data policy
requirements of the client. If both servers meet the privacy
preserving data policy requirements of the client, it can select to
use the local DNS server. In addition, the cryptographically signed
privacy statement allows a DNS-over-TLS or DNS-over-HTTPS client to
Reddy, et al. Expires April 5, 2020 [Page 3]
Internet-Draft Asserted DNS server privacy policy October 2019
securely determine whether the local DNS server performs DNS-based
content filtering, and if the local server meets the privacy
preserving data policy requirements of the client, the client can
continue to use the local DNS-over-TLS server to resolve DNS queries
and does not have to switch to the pre-configured public resolver.
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.
(D)TLS is used for statements that apply to both Transport Layer
Security [RFC8446] and Datagram Transport Layer Security [RFC6347].
Specific terms are used for any statement that applies to either
protocol alone.
This document uses the terms defined in [RFC8499].
3. Privacy 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 conveniently
accommodate asserted privacy policy information of the DNS-over-TLS
or DNS-over-HTTPS 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. JWT defines a set of claims that are represented
by specified JSON objects which can be extended with custom keys for
specific applications. The next sections define the header and
claims that MUST be minimally used with JWT and JWS for privacy
assertion token.
The privacy assertion token (PAT) specifically uses this token format
and defines claims that convey the privacy policy information of DNS-
over-TLS or DNS-over-HTTPS server. The signer of a PAT object may or
may not correspond to the DNS server's domain. The PAT object can be
validated by the DNS client, and if the DNS server meets the privacy
preserving data policy requirements of the client and/or end user, it
can switch to the privacy-enabling DNS server discovered in the
Reddy, et al. Expires April 5, 2020 [Page 4]
Internet-Draft Asserted DNS server privacy policy October 2019
located network. The creation of the PAT object is performed by an
entity that is authoritative to assert the DNS server privacy policy
information. This authority is represented by the certificate
credentials and the signature, and PAT object is created and the
client can retrieve the PAT object using the method discussed in
[I-D.ietf-dnsop-resolver-information].
For example, the PAT object could be created by the domain hosting
the DNS-over-TLS or DNS-over-HTTPS server, or by a third party who
performed privacy and security audit of the DNS-over-TLS or DNS-over-
HTTPS server. The DNS client needs to have the capability to verify
the PAT token and the digital signature. The PAT associated
certificate is used to validate the authority of the originating
signer, generally via a certificate chain to the trust anchor for the
DNS client.
4. PAT Header
The JWS token header is a JOSE header, [RFC7515] Section 4, that
defines the type and encryption algorithm used in the token.
PAT header should include, at a minimum, the header parameters
defined in the next three subsections.
4.1. "typ" (Type) Header Parameter
The "typ" (Type) Header Parameter is defined in JWS [RFC7515]
Section 4.1.9 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.
4.2. "alg" (Algorithm) Header Parameter
The "alg" (Algorithm) Header Parameter is defined in JWS [RFC7515]
Section 4.1.1. This definition includes the ability to specify the
use of a cryptographic algorithm for the signature part of the JWS.
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 JWA
[RFC7518] Section 3.4. Implementations MAY support other algorithms
registered in the JSON Web Signature and Encryption Algorithms
registry created by [RFC7518]. The contents of that registry may be
updated in the future depending on cryptographic strength
requirements guided by current security best practice. The
Reddy, et al. Expires April 5, 2020 [Page 5]
Internet-Draft Asserted DNS server privacy policy October 2019
mandatory-to-support algorithm for PAT tokens may likewise be updated
in future updates to this document.
Implementations of PAT digital signatures using ES256 as defined
above SHOULD use deterministic ECDSA if/when supported for the
reasons stated in [RFC6979].
4.3. "x5u" (X.509 URL) Header Parameter
As defined in JWS [RFC7515] Section 4.1.5., 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 JWS [RFC7515] section 4.1.5, this would correspond to
an HTTPS or DNSSEC resource using integrity protection.
4.4. Example PAT header
An example of the header, would be the following, including the
specified pat type, ES256 algorithm, and a URI referencing the
network location of the certificate needed to validate the PAT
signature.
{
"typ":"pat",
"alg":"ES256",
"x5u":"https://cert.example.com/pat.cer"
}
5. PAT Payload
The token claims consists of the privacy policy information of the
DNS server which needs to be verified at the DNS client. These
claims follow the definition of a JWT claim [RFC7519] Section 4 and
are encoded as defined by the JWS Payload [RFC7515] Section 3.
PAT defines the use of a standard JWT defined claim as well as custom
claims corresponding to the DNS-over-TLS or DNS-over-HTTPS servers.
Any claim names MUST use the US-ASCII character set. Any claim
values can contain characters that are outside the US-ASCII range,
however MUST follow the default JSON serialization defined in
[RFC7519] Section 7.
Reddy, et al. Expires April 5, 2020 [Page 6]
Internet-Draft Asserted DNS server privacy policy October 2019
5.1. JWT defined claims
5.1.1. "iat" - Issued At claim
The JSON claim MUST include the "iat" [RFC7519] Section 4.1.6 defined
claim Issued At. As defined the "iat" should be set to the date and
time of issuance of the JWT. The time value should be of the format
defined in [RFC7519] Section 2 NumericDate.
5.1.2. "exp" - Expiration Time claim
The JSON claim MUST include the "exp" [RFC7519] Section 4.1.4 defined
claim Expiration Time. As defined 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 generally expire after a
reasonable duration. A short expiration time for the PAT object
periodically reaffirms the privacy policy information of the DNS
server to the client and ensures the client does not use outdated
privacy policy information. If the client knows the PAT object has
expired, it makes another request to get the new PAT object from the
DNS server.
5.2. PAT specific claims
5.2.1. 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. Currently, these
identities can be represented as either authentication domain name
(ADN) (defined in [RFC8310]) or Uniform Resource Indicators (URI).
5.2.1.1. "adn" - authentication domain name identity
If the DNS server identity is a 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, 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 DNS-over-HTTPS protocol is supported by the DNS server,
the DNS client uses the https URI scheme (Section 3 of [RFC8484]).
Reddy, et al. Expires April 5, 2020 [Page 7]
Internet-Draft Asserted DNS server privacy policy October 2019
5.2.2. "privinfo" (Privacy Information) Claim
The "privinfo" claim MUST be formatted as a JSON object. The
"privinfo" claim contains the privacy policy information of the DNS
server, it includes the following attributes:
ipaddresspii: If the client IP address is Personally Identifiable
Information (PII) data or non PII-data. If client IP address is
PII, the parameter value is set to 'true'. This is a mandatory
attribute.
logging: If the transaction data (e.g., DNS messages) is logged and
the duration that data is stored. A value of negative one (-1)
indicates indefinite duration of logging transaction data. A
value of zero (0) indicates no logging. Logging duration is
represented in hours. If any of the attributes 'useridentity',
'notifyuser' and 'analytics' are not set to the value zero,
'logging' attribute MUST NOT be set to the value zero. This is a
mandatory attribute.
useridentity: If the user identity that sent the DNS query is logged
and the duration that data is retained. User identity includes
things such as username, IP address, MAC address, user DNS query
patterns or any other personally identifiable data. The server
should also discard or minimize correlation data (Section 5.2.4 of
[I-D.ietf-dprive-bcp-op]) that can be used to identify the end
user. A value of negative one (-1) indicates indefinite duration
of logging user identity. A value of zero (0) indicates no
logging. Logging duration is represented in hours. This is a
mandatory attribute.
filtering: If the DNS server changes some of the answers that it
returns based on policy criteria, such as to prevent access to
malware sites or objectionable content. This optional attribute
has the following structure:
malwareblocking: The DNS server offers malware blocking service.
If access to domains is blocked on threat data, the parameter
value is set to 'true'.
policyblocking: If access to domains is blocked on a blacklist or
objectionable content, the parameter value is set to 'true'.
notifyuser: If the transaction data is logged to notify the user
access to certain domains is blocked, the period for which the
transaction data is stored. A value of negative one (-1)
indicates indefinite duration of logging transaction data to
notify the user. A value of zero (0) indicates no logging.
Reddy, et al. Expires April 5, 2020 [Page 8]
Internet-Draft Asserted DNS server privacy policy October 2019
Logging duration is represented in hours. This is an optional
attribute.
analytics: If the transaction data is logged for analytics (e.g., To
detect malicious domains), the period for which the transaction
data is stored. A value of negative one (-1) indicates indefinite
duration of logging transaction data for analytics. A value of
zero (0) indicates no logging. Logging duration is represented in
hours. This is an optional attribute.
sharedata: If the transaction data is shared with partners or not,
and if the transaction data is shared with partners, the names of
the partners. If anonymized data or client identifiable data is
shared with partners. The term "anonymization" is defined in
Section 5.2.2 of [I-D.ietf-dprive-bcp-op]. This mandatory
attribute has the following structure:
sharepartners: If transaction data is shared with partners, the
parameter value is set to 'true'.
partners: List of partner names. If 'sharepartners' value is set
to false, 'partners' MUST NOT be present in the 'sharedata'
structure.
anonymizeddata: If anonymized transaction data is shared with
partners, the parameter value is set to 'true'. If
'sharepartners' value is set to false, 'anonymizeddata' MUST
NOT be present in the 'sharedata' structure.
transferdata: If the transaction data is shared or sold to third
parties. If the parameter value is set to 'true', means share or
sell data to third parties. This is a mandatory attribute.
qnameminimization: If the DNS server implements QNAME minimisation
[RFC7816] to improve DNS privacy. If the parameter value is set
to 'true', QNAME minimisation is supported by the DNS server.
This is a mandatory attribute.
privacyurl: A URL that points to the privacy policy information of
the DNS server. This is a mandatory attribute.
auditurl: A URL that points to the security assessment report of the
DNS server by a third party auditor. This is an optional
attribute.
upstreamservers: The local DNS server can be configured as a
Forwarding DNS server [RFC8499] relying on the upstream resolver
(e.g., at an ISP) to perform recursive DNS lookups. The client
Reddy, et al. Expires April 5, 2020 [Page 9]
Internet-Draft Asserted DNS server privacy policy October 2019
needs to discover the privacy policy information of both the
forwarder and recursive resolvers. This optional attribute has
the following structure:
securechannel: If DNS-over-TLS or DNS-over-HTTPS is used to
encrypt the DNS messages exchanged between the local DNS server
and recursive resolver, the parameter value is set to 'true'.
upstreamserverspat: The PAT object of the upstream DNS server.
If a local DNS server is configured as a Forwarding DNS server,
its PAT MUST include the PAT object of the upstream resolver it
is using. If the upstream DNS resolver does not communicate
its privacy policy, the attribute value must be set to empty
string. The client can combine the local and upstream
resolver's privacy policies, always combining for the worse
privacy values. For example, if the local server does not log
queries but the upstream resolver does log queries, the
combined PAT policy would indicate queries are logged and the
client can evaluate if its privacy preserving data policy
requirements are met. The Forwarding DNS server is typically
configured with both primary and secondary resolvers as a
backup mechanism to handle primary server failure. If the
local DNS server is configured to use primary and secondary
resolvers, 'upstreamserverspat' MUST include two entries in the
array. If the local DNS server is acting as a forwarder, it
RECOMMENDED that the DNS client requests the privacy policy
information of the server every time the connection is re-
established with the server. It allows the client to detect
change in the local DNS server configuration to use an
alternate resolver.
5.2.3. Example
The below Figure shows an example of privacy policy information.
Reddy, et al. Expires April 5, 2020 [Page 10]
Internet-Draft Asserted DNS server privacy policy October 2019
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"privinfo": {
"ipaddresspii":true,
"logging": 24,
"useridentity": 24,
"sharedata": {
"sharepartners": false
},
"transferdata":false,
"privacyurl": "https://example.com/commitment-to-privacy/"
}
}
6. PAT Signature
The signature of the PAT is created as specified by JWS [RFC7515]
Section 5.1 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 4
and Section 5, and JSON serialization rules in Section 8 of this
document 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 privacy policy information
will be attested using "Organization Validation" (OV) or "Extended
Validation" (EV) certificates to avoid bad actors taking advantage of
this mechanism to advertise DNS-over-TLS and DNS-over-HTTPS servers
for illegitimate and fraudulent purposes meant to trick DNS clients
into believing that they are using a legitimate DNS-over-TLS or DNS-
over-HTTPS server hosted to provide privacy for DNS transactions.
Alternatively, the DNS client will have 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 browser
trust chain because that would allow any arbitrary entity to operate
a DNS server and assert any sort of privacy policy.
Appendix A of this document has a detailed example of how to follow
the steps to create the JWS Signature.
JWS [RFC7515] Section 5.1 Step 7 JWS JSON serialization is supported
for PAT to enable multiple signatures to be applied to the PAT
object. For example, the PAT object can be cryptographically signed
Reddy, et al. Expires April 5, 2020 [Page 11]
Internet-Draft Asserted DNS server privacy policy October 2019
by the domain hosting the DNS server and by a third party who
performed privacy and security audit of the DNS server.
Appendix B of this document has a example of complete JWS JSON
serialization representation with multiple signatures.
JWS [RFC7515] Section 5.1 Step 8 describes the method to create the
final JWS Compact Serialization form of the PAT Token.
7. Extending PAT
PAT includes the minimum set of claims needed to securely assert the
privacy policy information of the DNS server. JWT supports a
straight forward way 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 ([RFC7519] Section 10.1). 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.
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 Step 1 of [RFC7638].
1. The JSON object MUST contain no whitespace or line breaks before
or after any syntactic elements.
2. JSON objects MUST have the keys ordered lexicographically by the
Unicode [UNICODE] code points of the member names.
3. JSON value literals MUST be lowercase.
4. JSON numbers are to be encoded as integers unless the field is
defined to be encoded otherwise.
5. Encoding rules MUST be applied recursively to member values and
array values.
Reddy, et al. Expires April 5, 2020 [Page 12]
Internet-Draft Asserted DNS server privacy policy October 2019
8.1. Example PAT deterministic JSON form
This section demonstrates the deterministic JSON serialization for
the example PAT Payload shown in Section 5.2.3.
The initial JSON object is shown here:
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"privinfo": {
"ipaddresspii":true,
"logging": 24,
"useridentity": 24,
"sharedata": {
"sharepartners": false
},
"transferdata":false,
"privacyurl": "https://example.com/commitment-to-privacy/"
}
}
The parent members of the JSON object are as follows, in
lexicographic order: "exp", "iat", "privinfo", "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,"privinfo":{"ipaddresspii":true,
"logging":24,"privacyurl":"https://example.com/commitment-to-privacy/",
"sharedata":{"sharepartners":false},"transferdata":false,
"useridentity":24},"server":{"adn":["example.com"]}}
9. 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).
Separately, the user is expected to indicate to their system their
PAT privacy requirements (e.g., logging, etc.). By doing so, the DNS
client can automatically discover local DNS-over-TLS or DNS-over-
HTTPS server, validate the PAT signature and check if the PAT
complies with user's privacy needs, prior to using that DNS-over-TLS
or DNS-over-HTTPS server for DNS queries. The client MAY also
Reddy, et al. Expires April 5, 2020 [Page 13]
Internet-Draft Asserted DNS server privacy policy October 2019
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 consent is obtained prior
to using a locally-discovered DNS-over-TLS or DNS-over-HTTPS server
for DNS queries.
An average user may not be able to indicate the privacy preserving
data policy requirements to the system. For such users, the DNS
client should auto check if the PAT complies with typical users
privacy needs. For example, the client by default does not select
the local DNS-over-TLS or DNS-over-HTTPS server if it shares non-
anonymized DNS transaction data with partners or if it logs the DNS
transaction data for a very long duration.
10. 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 privacy policy information of the DNS server being
asserted. Bad actors can host DNS-over-TLS and DNS-over-HTTPS
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 DNS-over-TLS and DNS-over-HTTPS servers, and get
the DNS server certificate signed by a CA. The privacy 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.
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 privacy policy of the DNS server like sharing
identifiable transaction data with partners can cause a disagreement
between the PAT object and the DNS server operation. In other words,
the DNS server might have complied with the privacy policy when it
was audited (by the 3rd party) but could now be in non-compliance
with its privacy policy, 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 privacy policy information and
limits the damage from change in privacy policy and mis-issuance.
11. IANA Considerations
Reddy, et al. Expires April 5, 2020 [Page 14]
Internet-Draft Asserted DNS server privacy policy October 2019
11.1. Media Type Registration
11.1.1. 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: [RFCThis]
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
Reddy, et al. Expires April 5, 2020 [Page 15]
Internet-Draft Asserted DNS server privacy policy October 2019
11.2. JSON Web Token Claims Registration
11.2.1. Registry Contents Additions Requested
o Claim Name: "server"
o Claim Description: DNS server identity
o Change Controller: IESG
o Specification Document(s): Section 5.2.1 of [TODO this document]
o Claim Name: "privinfo"
o Claim Description: Privacy policy information of DNS server.
o Change Controller: IESG
o Specification Document(s): Section 5.2.2 of [TODO this document]
11.3. DNS Resolver Information Registration
IANA will add the names ipaddresspii, logging, useridentity,
filtering, notifyuser, analytics, sharedata, transferdata,
qnameminimization, privacyurl, auditurl and upstreamserverpat to the
DNS Resolver Information registry defined in Section 5.2 of
[I-D.ietf-dnsop-resolver-information].
12. Acknowledgments
This specification leverages some of the work that has been done in
[RFC8225]. Thanks to Ted Lemon and Shashank Jain for the discussion
and comments.
13. References
13.1. Normative References
[I-D.ietf-dnsop-resolver-information]
Sood, P., Arends, R., and P. Hoffman, "DNS Resolver
Information Self-publication", draft-ietf-dnsop-resolver-
information-00 (work in progress), August 2019.
[I-D.ietf-dnsop-terminology-bis]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", draft-ietf-dnsop-terminology-bis-14 (work in
progress), September 2018.
Reddy, et al. Expires April 5, 2020 [Page 16]
Internet-Draft Asserted DNS server privacy policy October 2019
[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>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[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>.
Reddy, et al. Expires April 5, 2020 [Page 17]
Internet-Draft Asserted DNS server privacy policy October 2019
[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>.
[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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[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>.
[UNICODE] The Unicode Consortium, "The Unicode Standard", June 2016,
<http://www.unicode.org/versions/latest/>.
13.2. Informative References
[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-03 (work in
progress), July 2019.
[I-D.reddy-dprive-bootstrap-dns-server]
K, R., Wing, D., Richardson, M., and M. Boucadair, "A
Bootstrapping Procedure to Discover and Authenticate DNS-
over-(D)TLS and DNS-over-HTTPS Servers", draft-reddy-
dprive-bootstrap-dns-server-04 (work in progress), June
2019.
[RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
DOI 10.17487/RFC7626, August 2015,
<https://www.rfc-editor.org/info/rfc7626>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
Reddy, et al. Expires April 5, 2020 [Page 18]
Internet-Draft Asserted DNS server privacy policy October 2019
[RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
<https://www.rfc-editor.org/info/rfc8225>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
Appendix A. Example ES256 based PAT JWS Serialization and Signature
For PAT, there will always be a JWS with the following members:
o "protected", with the value BASE64URL(UTF8(JWS Protected Header))
o "payload", with the value BASE64URL (JWS Payload)
o "signature", with the value BASE64URL(JWS Signature)
This example will follow the steps in JWS [RFC7515] Section 5.1,
steps 1-6 and 8 and incorporates the additional serialization steps
required for PAT.
Step 1 for JWS references the JWS Payload, an example PAT Payload is
as follows:
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"privinfo": {
"ipaddresspii":true,
"logging": 24,
"useridentity": 24,
"sharedata": {
"sharepartners": false
},
"transferdata":false,
"privacyurl": "https://example.com/commitment-to-privacy/"
}
}
This would be serialized to the form (with line break used for
display purposes only):
Reddy, et al. Expires April 5, 2020 [Page 19]
Internet-Draft Asserted DNS server privacy policy October 2019
{"exp":1443640345,"iat":1443208345,"privinfo":{"ipaddresspii":true,
"logging":24,"privacyurl":"https://example.com/commitment-to-privacy/",
"sharedata":{"sharepartners":false},"transferdata":false,
"useridentity":24},"server":{"adn":["example.com"]}}
Step 2 Computes the BASE64URL(JWS Payload) producing this value (with
line break used for display purposes only):
eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicHJpdmluZm8iOnsi
aXBhZGRyZXNzcGlpIjp0cnVlLCJsb2dnaW5nIjoyNCwicHJpdmFjeXVybCI6Imh0
dHBzOi8vZXhhbXBsZS5jb20vY29tbWl0bWVudC10by1wcml2YWN5LyIsInNoYXJl
ZGF0YSI6eyJzaGFyZXBhcnRuZXJzIjpmYWxzZX0sInRyYW5zZmVyZGF0YSI6ZmFs
c2UsInVzZXJpZGVudGl0eSI6MjR9LCJzZXJ2ZXIiOnsiYWRuIjpbImV4YW1wbGUu
Y29tIl19fQ
For Step 3, an example PAT Protected Header comprising the JOSE
Header is as follows:
{
"alg":"ES256",
"typ":"pat",
"x5u":"https://cert.example.com/pat.cer"
}
This would be serialized to the form (with line break used for
display purposes only):
{"alg":"ES256","typ":"pat","x5u":"https://cert.example.com
/pat.cer"}
Step 4 Performs the BASE64URL(UTF8(JWS Protected Header)) operation
and encoding produces this value (with line break used for display
purposes only):
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
eGFtcGxlLmNvbS9wYXQuY2VyIn0
Step 5 and Step 6 performs the computation of the digital signature
of the PAT Signing Input ASCII(BASE64URL(UTF8(JWS Protected
Header)) || '.' || BASE64URL(JWS Payload)) using ES256 as the
algorithm and the BASE64URL(JWS Signature).
LEyaZpkJWVeJiQXdh6stCUo5VnLO56p9nTNsG8xhqpQMoJWc4j46Ze_43wPG-vHb
Xq7BaVIfdb_Lw3BcKr92Cw
Reddy, et al. Expires April 5, 2020 [Page 20]
Internet-Draft Asserted DNS server privacy policy October 2019
Step 8 describes how to create the final PAT token, concatenating the
values in the order Header.Payload.Signature with period ('.')
characters. For the above example values this would produce the
following (with line breaks between period used for readability
purposes only):
eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHBzOi8vY2VydC5l
eGFtcGxlLmNvbS9wYXQuY2VyIn0
.
eyJleHAiOjE0NDM2NDAzNDUsImlhdCI6MTQ0MzIwODM0NSwicHJpdmluZm8iOnsi
aXBhZGRyZXNzcGlpIjp0cnVlLCJsb2dnaW5nIjoyNCwicHJpdmFjeXVybCI6Imh0
dHBzOi8vZXhhbXBsZS5jb20vY29tbWl0bWVudC10by1wcml2YWN5LyIsInNoYXJl
ZGF0YSI6eyJzaGFyZXBhcnRuZXJzIjpmYWxzZX0sInRyYW5zZmVyZGF0YSI6ZmFs
c2UsInVzZXJpZGVudGl0eSI6MjR9LCJzZXJ2ZXIiOnsiYWRuIjpbImV4YW1wbGUu
Y29tIl19fQ
.
1ysb-n4O3YeN7HwPtzMP3SCEz28I80c78Lke4D_DRiwT8_-zi0p8IwmNU9778lOy
Ub9WZehA89G4VMx8DDpm0Q
A.1. X.509 Private Key in PKCS#8 format for ES256 Example**
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgevZzL1gdAFr88hb2
OF/2NxApJCzGCEDdfSp6VQO30hyhRANCAAQRWz+jn65BtOMvdyHKcvjBeBSDZH2r
1RTwjmYSi9R/zpBnuQ4EiMnCqfMPWiZqB4QdbAd0E7oH50VpuZ1P087G
-----END PRIVATE KEY-----
A.2. X.509 Public Key for ES256 Example**
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEEVs/o5+uQbTjL3chynL4wXgUg2R9
q9UU8I5mEovUf86QZ7kOBIjJwqnzD1omageEHWwHdBO6B+dFabmdT9POxg==
-----END PUBLIC KEY-----
Appendix B. Complete JWS JSON Serialization Representation with
multiple Signatures
The JWS payload used in this example as follows.
Reddy, et al. Expires April 5, 2020 [Page 21]
Internet-Draft Asserted DNS server privacy policy October 2019
{
"server":{
"adn":["example.com"]
},
"iat":1443208345,
"exp":1443640345,
"privinfo": {
"ipaddresspii":true,
"logging": 24,
"useridentity": 24,
"sharedata": {
"sharepartners": false
},
"transferdata":false,
"privacyurl": "https://example.com/commitment-to-privacy/",
"auditurl": "https://audit-example.com/privacyaudit"
}
}
This would be serialized to the form (with line break used for
display purposes only):
{"auditurl":"https://audit-example.com/privacyaudit","exp":1443640345,
"iat":1443208345,"privinfo":{"ipaddresspii":true,"logging":24,
"privacyurl":"https://example.com/commitment-to-privacy/",
"sharedata":{"sharepartners":false},"transferdata":false,
"useridentity":24},"server":{"adn":["example.com"]}}
The JWS protected Header value used for the first signature is same
as that used in the example in Appendix A. The X.509 private key
used for generating the first signature is same as that used in the
example in Appendix A.1.
The JWS Protected Header value used for the second signature is:
{
"alg":"ES384",
"typ":"pat",
"x5u":"https://cert.audit-example.com/pat.cer"
}
The complete JWS JSON Serialization for these values is as follows
(with line breaks within values for display purposes only):
Reddy, et al. Expires April 5, 2020 [Page 22]
Internet-Draft Asserted DNS server privacy policy October 2019
{
"payload":
"eyJhdWRpdHVybCI6Imh0dHBzOi8vYXVkaXQtZXhhbXBsZS5jb20vcHJpdmFjeWF
1ZGl0IiwiZXhwIjoxNDQzNjQwMzQ1LCJpYXQiOjE0NDMyMDgzNDUsInByaXZpbmZ
vIjp7ImlwYWRkcmVzc3BpaSI6dHJ1ZSwibG9nZ2luZyI6MjQsInByaXZhY3l1cmw
iOiJodHRwczovL2V4YW1wbGUuY29tL2NvbW1pdG1lbnQtdG8tcHJpdmFjeS8iLCJ
zaGFyZWRhdGEiOnsic2hhcmVwYXJ0bmVycyI6ZmFsc2V9LCJ0cmFuc2ZlcmRhdGE
iOmZhbHNlLCJ1c2VyaWRlbnRpdHkiOjI0fSwic2VydmVyIjp7ImFkbiI6WyJleGF
tcGxlLmNvbSJdfX0",
"signatures":[
{"protected":"eyJhbGciOiJFUzI1NiIsInR5cCI6InBhdCIsIng1dSI6Imh0dHB
zOi8vY2VydC5leGFtcGxlLmNvbS9wYXQuY2VyIn0",
"signature":
"VeX23b4UNTRE358iXJGBnSnMXkIfrEYeZwA8aVKA1In-Nz5lpGVFXIjArnUY7T
D9vMR01jUzTy4qVbtA0smbUA"},
{"protected":"eyJhbGciOiJFUzM4NCIsInR5cCI6InBhdCIsIng1dSI6Imh0dHB
zOi8vY2VydC5hdWRpdC1leGFtcGxlLmNvbS9wYXQuY2VyIn0",
"signature":
"PKLgW0O3YZAv5ZlIMbQqOgCegAT_TUo6fshOuuGrPqBSYRgIb2ApfvCENzdp-f
rKQEVUTWj2odSzMaEKBkjIv49GdEEvAxIy6C5uNzugfsGZswu7gyY8-9mZ_OFV
-nWF"}]
}
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
Reddy, et al. Expires April 5, 2020 [Page 23]
Internet-Draft Asserted DNS server privacy policy October 2019
Dan Wing
Citrix Systems, Inc.
USA
Email: dwing-ietf@fuggles.com
Michael C. Richardson
Sandelman Software Works
USA
Email: mcr+ietf@sandelman.ca
Reddy, et al. Expires April 5, 2020 [Page 24]