-
Notifications
You must be signed in to change notification settings - Fork 3
/
Copy pathdraft-add-server-selection-information-01.txt
1288 lines (853 loc) · 47.2 KB
/
draft-add-server-selection-information-01.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
ADD WG T. Reddy
Internet-Draft McAfee
Intended status: Standards Track D. Wing
Expires: October 1, 2020 Citrix
M. Richardson
Sandelman Software Works
M. Boucadair
Orange
March 30, 2020
DNS Server Selection: DNS Server Information with Assertion Token
draft-reddy-add-server-policy-selection-01
Abstract
The document defines a mechanism that allows communication of DNS
resolver information to DNS clients for use in 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 DNS-over-TLS and DNS-over-HTTPS servers
that are either public resolvers or are discovered on 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 October 1, 2020.
Reddy, et al. Expires October 1, 2020 [Page 1]
Internet-Draft DNS Server Info with Assertion Token March 2020
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Sample Use Cases . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Policy Assertion Token (PAT): Overview . . . . . . . . . . . 5
5. PAT Header . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. 'typ' (Type) Header Parameter . . . . . . . . . . . . . . 6
5.2. 'alg' (Algorithm) Header Parameter . . . . . . . . . . . 6
5.3. 'x5u' (X.509 URL) Header Parameter . . . . . . . . . . . 7
5.4. An Example of PAT Header . . . . . . . . . . . . . . . . 7
6. PAT Payload . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. JWT Defined Claims . . . . . . . . . . . . . . . . . . . 8
6.1.1. 'iat' - Issued At Claim . . . . . . . . . . . . . . . 8
6.1.2. 'exp' - Expiration Time Claim . . . . . . . . . . . . 8
6.2. PAT Specific Claims . . . . . . . . . . . . . . . . . . . 8
6.2.1. DNS Server Identity Claims . . . . . . . . . . . . . 8
6.2.2. 'policyinfo' (Policy Information) Claim . . . . . . . 9
6.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 10
7. PAT Signature . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Extending PAT . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Deterministic JSON Serialization . . . . . . . . . . . . . . 11
9.1. Example PAT Deterministic JSON Form . . . . . . . . . . . 12
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
11. Security Considerations . . . . . . . . . . . . . . . . . . . 13
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
12.1. Media Type Registration . . . . . . . . . . . . . . . . 14
12.1.1. Media Type Registry Contents Additions Requested . . 14
12.2. JSON Web Token Claims Registration . . . . . . . . . . . 15
12.2.1. Registry Contents Additions Requested . . . . . . . 15
12.3. DNS Resolver Information Registration . . . . . . . . . 15
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
Reddy, et al. Expires October 1, 2020 [Page 2]
Internet-Draft DNS Server Info with Assertion Token March 2020
14.1. Normative References . . . . . . . . . . . . . . . . . . 15
14.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Example ES256 based PAT JWS Serialization and
Signature . . . . . . . . . . . . . . . . . . . . . 18
A.1. X.509 Private Key in PKCS#8 Format for ES256 Example** . 20
A.2. X.509 Public Key for ES256 Example** . . . . . . . . . . 21
Appendix B. Complete JWS JSON Serialization Representation with
multiple Signatures . . . . . . . . . . . . . . . . 21
B.1. X.509 Private Key in PKCS#8 format for E384 Example** . . 22
B.2. X.509 Public Key for ES384 Example** . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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. Two protocols that provide ways to increase DNS
privacy between DNS clients and servers are DNS-over-HTTPS (DoH)
[RFC8484] and DNS-over-TLS (DoT) [RFC7858].
DNS clients can discover and authenticate DoH and DoT servers
provided by a local network, for example using the technique proposed
in [I-D.btw-add-home]. If the mechanism used to discovered the DoH/
DoT server is insecure, the DNS client needs evidence about the DoH/
DoT 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 a
DoT/DoH 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
and use that information to fed a DNS server selection procedure.
The following parameters are supported in this version:
Reddy, et al. Expires October 1, 2020 [Page 3]
Internet-Draft DNS Server Info with Assertion Token March 2020
Malware blocking: Indicates whether the DNS server offers malware
blocking service.
Policy blocking: Indicates whether the DNS server maintains a block-
list (e.g., imposed by regulation).
QNAME minimization: Indicates whether the DNS server implements
QNAME minimisation [RFC7816].
The cryptographically signed policy allows a DNS client to 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.
Note that the proposed mechanism can also be used by DNS clients to
cryptographically validate the Do53 resolver information.
2. Sample Use Cases
The mechanism for a DNS server to communicate its cryptographically
signed policies to a DNS client contributes to solve the following
problems in various deployments:
o The DoH/DoT 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 DoH/DoT 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.
Reddy, et al. Expires October 1, 2020 [Page 4]
Internet-Draft DNS Server Info with Assertion Token March 2020
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 DoH/DoT 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.
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.
Reddy, et al. Expires October 1, 2020 [Page 5]
Internet-Draft DNS Server Info with Assertion Token March 2020
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. The client can retrieve the PAT object using the method
discussed in [I-D.ietf-dnsop-resolver-information]. The signature of
PAT object can be validated by the DNS client. If the signer and the
contents of the PAT object comply with the user's requirements, the
user's client software can use that DNS server.
The PAT object is signed by the DNS server's domain that is
authoritative to assert the DNS server policy information. This
authority is represented by the certificate credentials and the
signature.
For example, the PAT object could be created by the organization
hosting the DoH/DoT server and optionally by a third party who
performed privacy and security audit of the DoH/DoT server. The DNS
client needs to have the capability to verify the digital signature
and to parse the PAT object.
5. PAT Header
The JWS token header is a JOSE header (Section 4 of [RFC7515]) that
defines the type and encryption algorithm used in the token.
PAT header MUST include, at a minimum, the header parameters defined
in Sections 5.1, 5.2, and 5.3.
5.1. 'typ' (Type) Header Parameter
The 'typ' (Type) Header Parameter is defined Section 4.1.9 of
[RFC7515] to declare the media type of the complete JWS.
For PAT Token the 'typ' header MUST be the string 'pat'. This
represents that the encoded token is a JWT of type pat.
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.
Reddy, et al. Expires October 1, 2020 [Page 6]
Internet-Draft DNS Server Info with Assertion Token March 2020
For the creation and verification of PAT tokens and their digital
signatures, implementations MUST support ES256 as defined in
Section 3.4 of [RFC7518]. Implementations MAY support other
algorithms registered in the JSON Web Signature and Encryption
Algorithms registry created by [RFC7518]. The content of that
registry may be updated in the future depending on cryptographic
strength requirements guided by current security best practice. The
mandatory-to-support algorithm for PAT tokens may likewise be updated
in the future.
Implementations of PAT digital signatures using ES256 as defined
above SHOULD use deterministic ECDSA when supported for the reasons
stated in [RFC6979].
5.3. 'x5u' (X.509 URL) Header Parameter
As defined in Section 4.1.5 of [RFC7515], the 'x5u' header parameter
defines a URI [RFC3986] referring to the resource for the X.509
public key certificate or certificate chain [RFC5280] corresponding
to the key used to digitally sign the JWS. Generally, as defined in
Section 4.1.5 of [RFC7515] this corresponds to an HTTPS or DNSSEC
resource using integrity protection.
5.4. An Example of PAT Header
An example of the PAT header is shown in Figure 1. It includes the
specified PAT type, ES256 algorithm, and an URI referencing the
network location of the certificate needed to validate the PAT
signature.
{
"typ":"pat",
"alg":"ES256",
"x5u":"https://cert.example.com/pat.cer"
}
Figure 1: A PAT Header Example
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.
Reddy, et al. Expires October 1, 2020 [Page 7]
Internet-Draft DNS Server Info with Assertion Token March 2020
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 hash of the resolver information,
retreive the information again the expiration time, computes hash of
the newly retrieved resolver information and compares with the
previous hash to detect policy updates. A quality implementation can
perform automatic analysis and avoid presenting this information to
the user if the DNS server's policies have not changed.
6.2. PAT Specific Claims
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).
Reddy, et al. Expires October 1, 2020 [Page 8]
Internet-Draft DNS Server Info with Assertion Token March 2020
6.2.1.1. 'adn' - Authentication Domain Name Identity
If the DNS server identity is an ADN, the claim name representing the
identity MUST be 'adn'. The claim value for the 'adn' claim is the
ADN.
6.2.1.2. 'uri' - URI Identity
If the DNS server identity is of the form URI, as defined in
[RFC3986], the claim name representing the identity MUST be 'uri' and
the claim value is the URI form of the DNS server identity.
As a reminder, if DoH is supported by the DNS server, the DNS client
uses the https URI scheme (Section 3 of [RFC8484]).
6.2.2. 'policyinfo' (Policy Information) Claim
The 'policyinfo' claim MUST be formatted as a JSON object. The
'policyinfo' claim contains the policy information of the DNS server,
it includes the following attributes:
filtering: If the DNS server changes some of the answers that it
returns based on policy criteria, such as to prevent access to
malware sites or objectionable content. This optional attribute
has the following structure:
malwareblocking: The DNS server offers malware blocking service.
If access to domains is blocked on threat data, the parameter
value is set to 'true'.
policyblocking: If access to domains is blocked on a blacklist or
objectionable content, the parameter value is set to 'true'.
qnameminimization: If the DNS server implements QNAME minimisation
[RFC7816] to improve DNS privacy. If the parameter value is set
to 'true', QNAME minimisation is supported by the DNS server.
This is a mandatory attribute.
privacyurl: A URL that points to the privacy policy information of
the DNS server. This is a mandatory attribute.
auditurl: A URL that points to the security assessment report of the
DNS server by a third party auditor. This is an optional
attribute.
Reddy, et al. Expires October 1, 2020 [Page 9]
Internet-Draft DNS Server Info with Assertion Token March 2020
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 DoH/DoT servers for
illegitimate and fraudulent purposes meant to trick DNS clients into
believing that they are using a legitimate DoH/DoT 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.
Reddy, et al. Expires October 1, 2020 [Page 10]
Internet-Draft DNS Server Info with Assertion Token March 2020
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.
Reddy, et al. Expires October 1, 2020 [Page 11]
Internet-Draft DNS Server Info with Assertion Token March 2020
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 DoH/DoT server
in specific networks, validate the PAT signature and the user can
check if the human readable privacy policy information of the DNS
Reddy, et al. Expires October 1, 2020 [Page 12]
Internet-Draft DNS Server Info with Assertion Token March 2020
server complies with user's privacy needs, prior to using that DoH/
DoT 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 DoH/
DoT 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
installer input. If the DoH/DoT information is insecurely discovered
and not pre-configured in the IoT device, the client can validate the
Policy Assertion Token signature using the owner certificate
(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 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 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 the policy of the DNS server can cause a
disagreement between the auditor and the DNS server operation, hence
the PAT object needs to be also asserted by the domain hosting the
DNS server. In addition, the PAT object needs to have a short
expiration time (e.g., 7 days) to ensure the DNS server's domain re-
asserts the policy information and limits the damage from change in
policy and mis-issuance.
12. IANA Considerations
Reddy, et al. Expires October 1, 2020 [Page 13]
Internet-Draft DNS Server Info with Assertion Token March 2020
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, 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 October 1, 2020 [Page 14]
Internet-Draft DNS Server Info with Assertion Token March 2020
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 5.2 of [I-D.ietf-dnsop-resolver-information].
13. Acknowledgments
This specification leverages some of the work that has been done in
[RFC8225]. Thanks to Ted Lemon, Paul Wouters 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>.
Reddy, et al. Expires October 1, 2020 [Page 15]
Internet-Draft DNS Server Info with Assertion Token March 2020
[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>.
Reddy, et al. Expires October 1, 2020 [Page 16]
Internet-Draft DNS Server Info with Assertion Token March 2020
[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, "DNS-
over-HTTPS and DNS-over-TLS Server Discovery and
Deployment Considerations for Home and Mobile Networks",
draft-btw-add-home-04 (work in progress), March 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-14 (work in progress), January 2020.
[I-D.ietf-dnsop-resolver-information]
Sood, P., Arends, R., and P. Hoffman, "DNS Resolver
Information Self-publication", draft-ietf-dnsop-resolver-
information-01 (work in progress), February 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-08 (work in
progress), January 2020.
[RFC7626] Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
DOI 10.17487/RFC7626, August 2015,
<https://www.rfc-editor.org/info/rfc7626>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
Reddy, et al. Expires October 1, 2020 [Page 17]
Internet-Draft DNS Server Info with Assertion Token March 2020
[RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
<https://www.rfc-editor.org/info/rfc8225>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
[UNICODE] The Unicode Consortium, "The Unicode Standard", June 2016,
<http://www.unicode.org/versions/latest/>.
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: