summaryrefslogtreecommitdiffstats
path: root/security/pkix/lib/pkixocsp.cpp
blob: 215020f6769d6cba4ad9badb3bc6096b7a4543cf (plain)
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
1001
1002
1003
1004
1005
1006
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This code is made available to you under your choice of the following sets
 * of licensing terms:
 */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
/* Copyright 2013 Mozilla Contributors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <limits>

#include "pkix/pkix.h"
#include "pkixcheck.h"
#include "pkixutil.h"

namespace {

const size_t SHA1_DIGEST_LENGTH = 160 / 8;

} // namespace

namespace mozilla { namespace pkix {

// These values correspond to the tag values in the ASN.1 CertStatus
enum class CertStatus : uint8_t {
  Good = der::CONTEXT_SPECIFIC | 0,
  Revoked = der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 1,
  Unknown = der::CONTEXT_SPECIFIC | 2
};

class Context final
{
public:
  Context(TrustDomain& trustDomain, const CertID& certID, Time time,
          uint16_t maxLifetimeInDays, /*optional out*/ Time* thisUpdate,
          /*optional out*/ Time* validThrough)
    : trustDomain(trustDomain)
    , certID(certID)
    , time(time)
    , maxLifetimeInDays(maxLifetimeInDays)
    , certStatus(CertStatus::Unknown)
    , thisUpdate(thisUpdate)
    , validThrough(validThrough)
    , expired(false)
    , matchFound(false)
  {
    if (thisUpdate) {
      *thisUpdate = TimeFromElapsedSecondsAD(0);
    }
    if (validThrough) {
      *validThrough = TimeFromElapsedSecondsAD(0);
    }
  }

  TrustDomain& trustDomain;
  const CertID& certID;
  const Time time;
  const uint16_t maxLifetimeInDays;
  CertStatus certStatus;
  Time* thisUpdate;
  Time* validThrough;
  bool expired;

  Input signedCertificateTimestamps;

  // Keep track of whether the OCSP response contains the status of the
  // certificate we're interested in. Responders might reply without
  // including the status of any of the requested certs, we should
  // indicate a server failure in those cases.
  bool matchFound;

  Context(const Context&) = delete;
  void operator=(const Context&) = delete;
};

// Verify that potentialSigner is a valid delegated OCSP response signing cert
// according to RFC 6960 section 4.2.2.2.
static Result
CheckOCSPResponseSignerCert(TrustDomain& trustDomain,
                            BackCert& potentialSigner,
                            Input issuerSubject,
                            Input issuerSubjectPublicKeyInfo,
                            Time time)
{
  Result rv;

  // We don't need to do a complete verification of the signer (i.e. we don't
  // have to call BuildCertChain to verify the entire chain) because we
  // already know that the issuer is valid, since revocation checking is done
  // from the root to the parent after we've built a complete chain that we
  // know is otherwise valid. Rather, we just need to do a one-step validation
  // from potentialSigner to the issuer.
  //
  // It seems reasonable to require the KU_DIGITAL_SIGNATURE key usage on the
  // OCSP responder certificate if the OCSP responder certificate has a
  // key usage extension. However, according to bug 240456, some OCSP responder
  // certificates may have only the nonRepudiation bit set. Also, the OCSP
  // specification (RFC 6960) does not mandate any particular key usage to be
  // asserted for OCSP responde signers. Oddly, the CABForum Baseline
  // Requirements v.1.1.5 do say "If the Root CA Private Key is used for
  // signing OCSP responses, then the digitalSignature bit MUST be set."
  //
  // Note that CheckIssuerIndependentProperties processes
  // SEC_OID_OCSP_RESPONDER in the way that the OCSP specification requires us
  // to--in particular, it doesn't allow SEC_OID_OCSP_RESPONDER to be implied
  // by a missing EKU extension, unlike other EKUs.
  //
  // TODO(bug 926261): If we're validating for a policy then the policy OID we
  // are validating for should be passed to CheckIssuerIndependentProperties.
  TrustLevel unusedTrustLevel;
  rv = CheckIssuerIndependentProperties(trustDomain, potentialSigner, time,
                                        KeyUsage::noParticularKeyUsageRequired,
                                        KeyPurposeId::id_kp_OCSPSigning,
                                        CertPolicyId::anyPolicy, 0,
                                        unusedTrustLevel);
  if (rv != Success) {
    return rv;
  }

  // It is possible that there exists a certificate with the same key as the
  // issuer but with a different name, so we need to compare names
  // XXX(bug 926270) XXX(bug 1008133) XXX(bug 980163): Improve name
  // comparison.
  // TODO: needs test
  if (!InputsAreEqual(potentialSigner.GetIssuer(), issuerSubject)) {
    return Result::ERROR_OCSP_RESPONDER_CERT_INVALID;
  }

  // TODO(bug 926260): check name constraints

  rv = VerifySignedData(trustDomain, potentialSigner.GetSignedData(),
                        issuerSubjectPublicKeyInfo);

  // TODO: check for revocation of the OCSP responder certificate unless no-check
  // or the caller forcing no-check. To properly support the no-check policy, we'd
  // need to enforce policy constraints from the issuerChain.

  return rv;
}

enum class ResponderIDType : uint8_t
{
  byName = der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 1,
  byKey = der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 2
};

static inline Result OCSPResponse(Reader&, Context&);
static inline Result ResponseBytes(Reader&, Context&);
static inline Result BasicResponse(Reader&, Context&);
static inline Result ResponseData(
                       Reader& tbsResponseData,
                       Context& context,
                       const der::SignedDataWithSignature& signedResponseData,
                       const DERArray& certs);
static inline Result SingleResponse(Reader& input, Context& context);
static Result ExtensionNotUnderstood(Reader& extnID, Input extnValue,
                                     bool critical, /*out*/ bool& understood);
static Result RememberSingleExtension(Context& context, Reader& extnID,
                                      Input extnValue, bool critical,
                                      /*out*/ bool& understood);
static inline Result CertID(Reader& input,
                            const Context& context,
                            /*out*/ bool& match);
static Result MatchKeyHash(TrustDomain& trustDomain,
                           Input issuerKeyHash,
                           Input issuerSubjectPublicKeyInfo,
                           /*out*/ bool& match);
static Result KeyHash(TrustDomain& trustDomain,
                      Input subjectPublicKeyInfo,
                      /*out*/ uint8_t* hashBuf, size_t hashBufSize);

static Result
MatchResponderID(TrustDomain& trustDomain,
                 ResponderIDType responderIDType,
                 Input responderID,
                 Input potentialSignerSubject,
                 Input potentialSignerSubjectPublicKeyInfo,
                 /*out*/ bool& match)
{
  match = false;

  switch (responderIDType) {
    case ResponderIDType::byName:
      // XXX(bug 926270) XXX(bug 1008133) XXX(bug 980163): Improve name
      // comparison.
      match = InputsAreEqual(responderID, potentialSignerSubject);
      return Success;

    case ResponderIDType::byKey:
    {
      Reader input(responderID);
      Input keyHash;
      Result rv = der::ExpectTagAndGetValue(input, der::OCTET_STRING, keyHash);
      if (rv != Success) {
        return rv;
      }
      return MatchKeyHash(trustDomain, keyHash,
                          potentialSignerSubjectPublicKeyInfo, match);
    }

    MOZILLA_PKIX_UNREACHABLE_DEFAULT_ENUM
  }
}

static Result
VerifyOCSPSignedData(TrustDomain& trustDomain,
                     const der::SignedDataWithSignature& signedResponseData,
                     Input spki)
{
  Result rv = VerifySignedData(trustDomain, signedResponseData, spki);
  if (rv == Result::ERROR_BAD_SIGNATURE) {
    rv = Result::ERROR_OCSP_BAD_SIGNATURE;
  }
  return rv;
}

// RFC 6960 section 4.2.2.2: The OCSP responder must either be the issuer of
// the cert or it must be a delegated OCSP response signing cert directly
// issued by the issuer. If the OCSP responder is a delegated OCSP response
// signer, then its certificate is (probably) embedded within the OCSP
// response and we'll need to verify that it is a valid certificate that chains
// *directly* to issuerCert.
static Result
VerifySignature(Context& context, ResponderIDType responderIDType,
                Input responderID, const DERArray& certs,
                const der::SignedDataWithSignature& signedResponseData)
{
  bool match;
  Result rv = MatchResponderID(context.trustDomain, responderIDType,
                               responderID, context.certID.issuer,
                               context.certID.issuerSubjectPublicKeyInfo,
                               match);
  if (rv != Success) {
    return rv;
  }
  if (match) {
    return VerifyOCSPSignedData(context.trustDomain, signedResponseData,
                                context.certID.issuerSubjectPublicKeyInfo);
  }

  size_t numCerts = certs.GetLength();
  for (size_t i = 0; i < numCerts; ++i) {
    BackCert cert(*certs.GetDER(i), EndEntityOrCA::MustBeEndEntity, nullptr);
    rv = cert.Init();
    if (rv != Success) {
      return rv;
    }
    rv = MatchResponderID(context.trustDomain, responderIDType, responderID,
                          cert.GetSubject(), cert.GetSubjectPublicKeyInfo(),
                          match);
    if (rv != Success) {
      if (IsFatalError(rv)) {
        return rv;
      }
      continue;
    }

    if (match) {
      rv = CheckOCSPResponseSignerCert(context.trustDomain, cert,
                                       context.certID.issuer,
                                       context.certID.issuerSubjectPublicKeyInfo,
                                       context.time);
      if (rv != Success) {
        if (IsFatalError(rv)) {
          return rv;
        }
        continue;
      }

      return VerifyOCSPSignedData(context.trustDomain, signedResponseData,
                                  cert.GetSubjectPublicKeyInfo());
    }
  }

  return Result::ERROR_OCSP_INVALID_SIGNING_CERT;
}

static inline Result
MapBadDERToMalformedOCSPResponse(Result rv)
{
  if (rv == Result::ERROR_BAD_DER) {
    return Result::ERROR_OCSP_MALFORMED_RESPONSE;
  }
  return rv;
}

Result
VerifyEncodedOCSPResponse(TrustDomain& trustDomain, const struct CertID& certID,
                          Time time, uint16_t maxOCSPLifetimeInDays,
                          Input encodedResponse,
                          /*out*/ bool& expired,
                          /*optional out*/ Time* thisUpdate,
                          /*optional out*/ Time* validThrough)
{
  // Always initialize this to something reasonable.
  expired = false;

  Context context(trustDomain, certID, time, maxOCSPLifetimeInDays,
                  thisUpdate, validThrough);

  Reader input(encodedResponse);
  Result rv = der::Nested(input, der::SEQUENCE, [&context](Reader& r) {
    return OCSPResponse(r, context);
  });
  if (rv != Success) {
    return MapBadDERToMalformedOCSPResponse(rv);
  }
  rv = der::End(input);
  if (rv != Success) {
    return MapBadDERToMalformedOCSPResponse(rv);
  }
  if (!context.matchFound) {
    return Result::ERROR_OCSP_RESPONSE_FOR_CERT_MISSING;
  }

  expired = context.expired;

  switch (context.certStatus) {
    case CertStatus::Good:
      if (expired) {
        return Result::ERROR_OCSP_OLD_RESPONSE;
      }
      if (context.signedCertificateTimestamps.GetLength()) {
        Input sctList;
        rv = ExtractSignedCertificateTimestampListFromExtension(
          context.signedCertificateTimestamps, sctList);
        if (rv != Success) {
          return MapBadDERToMalformedOCSPResponse(rv);
        }
        context.trustDomain.NoteAuxiliaryExtension(
          AuxiliaryExtension::SCTListFromOCSPResponse, sctList);
      }
      return Success;
    case CertStatus::Revoked:
      return Result::ERROR_REVOKED_CERTIFICATE;
    case CertStatus::Unknown:
      return Result::ERROR_OCSP_UNKNOWN_CERT;
     MOZILLA_PKIX_UNREACHABLE_DEFAULT_ENUM
  }
}

// OCSPResponse ::= SEQUENCE {
//       responseStatus         OCSPResponseStatus,
//       responseBytes          [0] EXPLICIT ResponseBytes OPTIONAL }
//
static inline Result
OCSPResponse(Reader& input, Context& context)
{
  // OCSPResponseStatus ::= ENUMERATED {
  //     successful            (0),  -- Response has valid confirmations
  //     malformedRequest      (1),  -- Illegal confirmation request
  //     internalError         (2),  -- Internal error in issuer
  //     tryLater              (3),  -- Try again later
  //                                 -- (4) is not used
  //     sigRequired           (5),  -- Must sign the request
  //     unauthorized          (6)   -- Request unauthorized
  // }
  uint8_t responseStatus;

  Result rv = der::Enumerated(input, responseStatus);
  if (rv != Success) {
    return rv;
  }
  switch (responseStatus) {
    case 0: break; // successful
    case 1: return Result::ERROR_OCSP_MALFORMED_REQUEST;
    case 2: return Result::ERROR_OCSP_SERVER_ERROR;
    case 3: return Result::ERROR_OCSP_TRY_SERVER_LATER;
    case 5: return Result::ERROR_OCSP_REQUEST_NEEDS_SIG;
    case 6: return Result::ERROR_OCSP_UNAUTHORIZED_REQUEST;
    default: return Result::ERROR_OCSP_UNKNOWN_RESPONSE_STATUS;
  }

  return der::Nested(input, der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 0,
                     der::SEQUENCE, [&context](Reader& r) {
    return ResponseBytes(r, context);
  });
}

// ResponseBytes ::=       SEQUENCE {
//     responseType   OBJECT IDENTIFIER,
//     response       OCTET STRING }
static inline Result
ResponseBytes(Reader& input, Context& context)
{
  static const uint8_t id_pkix_ocsp_basic[] = {
    0x2B, 0x06, 0x01, 0x05, 0x05, 0x07, 0x30, 0x01, 0x01
  };

  Result rv = der::OID(input, id_pkix_ocsp_basic);
  if (rv != Success) {
    return rv;
  }

  return der::Nested(input, der::OCTET_STRING, der::SEQUENCE,
                     [&context](Reader& r) {
    return BasicResponse(r, context);
  });
}

// BasicOCSPResponse       ::= SEQUENCE {
//    tbsResponseData      ResponseData,
//    signatureAlgorithm   AlgorithmIdentifier,
//    signature            BIT STRING,
//    certs            [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL }
Result
BasicResponse(Reader& input, Context& context)
{
  Reader tbsResponseData;
  der::SignedDataWithSignature signedData;
  Result rv = der::SignedData(input, tbsResponseData, signedData);
  if (rv != Success) {
    if (rv == Result::ERROR_BAD_SIGNATURE) {
      return Result::ERROR_OCSP_BAD_SIGNATURE;
    }
    return rv;
  }

  // Parse certificates, if any
  NonOwningDERArray certs;
  if (!input.AtEnd()) {
    rv = der::Nested(input, der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 0,
                     der::SEQUENCE, [&certs](Reader& certsDER) -> Result {
      while (!certsDER.AtEnd()) {
        Input cert;
        Result rv = der::ExpectTagAndGetTLV(certsDER, der::SEQUENCE, cert);
        if (rv != Success) {
          return rv;
        }
        rv = certs.Append(cert);
        if (rv != Success) {
          return Result::ERROR_BAD_DER; // Too many certs
        }
      }
      return Success;
    });
    if (rv != Success) {
      return rv;
    }
  }

  return ResponseData(tbsResponseData, context, signedData, certs);
}

// ResponseData ::= SEQUENCE {
//    version             [0] EXPLICIT Version DEFAULT v1,
//    responderID             ResponderID,
//    producedAt              GeneralizedTime,
//    responses               SEQUENCE OF SingleResponse,
//    responseExtensions  [1] EXPLICIT Extensions OPTIONAL }
static inline Result
ResponseData(Reader& input, Context& context,
             const der::SignedDataWithSignature& signedResponseData,
             const DERArray& certs)
{
  der::Version version;
  Result rv = der::OptionalVersion(input, version);
  if (rv != Success) {
    return rv;
  }
  if (version != der::Version::v1) {
    // TODO: more specific error code for bad version?
    return Result::ERROR_BAD_DER;
  }

  // ResponderID ::= CHOICE {
  //    byName              [1] Name,
  //    byKey               [2] KeyHash }
  Input responderID;
  ResponderIDType responderIDType
    = input.Peek(static_cast<uint8_t>(ResponderIDType::byName))
    ? ResponderIDType::byName
    : ResponderIDType::byKey;
  rv = der::ExpectTagAndGetValue(input, static_cast<uint8_t>(responderIDType),
                                 responderID);
  if (rv != Success) {
    return rv;
  }

  // This is the soonest we can verify the signature. We verify the signature
  // right away to follow the principal of minimizing the processing of data
  // before verifying its signature.
  rv = VerifySignature(context, responderIDType, responderID, certs,
                       signedResponseData);
  if (rv != Success) {
    return rv;
  }

  // TODO: Do we even need to parse this? Should we just skip it?
  Time producedAt(Time::uninitialized);
  rv = der::GeneralizedTime(input, producedAt);
  if (rv != Success) {
    return rv;
  }

  // We don't accept an empty sequence of responses. In practice, a legit OCSP
  // responder will never return an empty response, and handling the case of an
  // empty response makes things unnecessarily complicated.
  rv = der::NestedOf(input, der::SEQUENCE, der::SEQUENCE,
                     der::EmptyAllowed::No, [&context](Reader& r) {
    return SingleResponse(r, context);
  });
  if (rv != Success) {
    return rv;
  }

  return der::OptionalExtensions(input,
                                 der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 1,
                                 ExtensionNotUnderstood);
}

// SingleResponse ::= SEQUENCE {
//    certID                       CertID,
//    certStatus                   CertStatus,
//    thisUpdate                   GeneralizedTime,
//    nextUpdate           [0]     EXPLICIT GeneralizedTime OPTIONAL,
//    singleExtensions     [1]     EXPLICIT Extensions{{re-ocsp-crl |
//                                              re-ocsp-archive-cutoff |
//                                              CrlEntryExtensions, ...}
//                                              } OPTIONAL }
static inline Result
SingleResponse(Reader& input, Context& context)
{
  bool match = false;
  Result rv = der::Nested(input, der::SEQUENCE, [&context, &match](Reader& r) {
    return CertID(r, context, match);
  });
  if (rv != Success) {
    return rv;
  }

  if (!match) {
    // This response does not reference the certificate we're interested in.
    // By consuming the rest of our input and returning successfully, we can
    // continue processing and examine another response that might have what
    // we want.
    input.SkipToEnd();
    return Success;
  }

  // We found a response for the cert we're interested in.
  context.matchFound = true;

  // CertStatus ::= CHOICE {
  //     good        [0]     IMPLICIT NULL,
  //     revoked     [1]     IMPLICIT RevokedInfo,
  //     unknown     [2]     IMPLICIT UnknownInfo }
  //
  // In the event of multiple SingleResponses for a cert that have conflicting
  // statuses, we use the following precedence rules:
  //
  // * revoked overrides good and unknown
  // * good overrides unknown
  if (input.Peek(static_cast<uint8_t>(CertStatus::Good))) {
    rv = der::ExpectTagAndEmptyValue(input,
                                     static_cast<uint8_t>(CertStatus::Good));
    if (rv != Success) {
      return rv;
    }
    if (context.certStatus != CertStatus::Revoked) {
      context.certStatus = CertStatus::Good;
    }
  } else if (input.Peek(static_cast<uint8_t>(CertStatus::Revoked))) {
    // We don't need any info from the RevokedInfo structure, so we don't even
    // parse it. TODO: We should mention issues like this in the explanation of
    // why we treat invalid OCSP responses equivalently to revoked for OCSP
    // stapling.
    rv = der::ExpectTagAndSkipValue(input,
                                    static_cast<uint8_t>(CertStatus::Revoked));
    if (rv != Success) {
      return rv;
    }
    context.certStatus = CertStatus::Revoked;
  } else {
    rv = der::ExpectTagAndEmptyValue(input,
                                     static_cast<uint8_t>(CertStatus::Unknown));
    if (rv != Success) {
      return rv;
    }
  }

  // http://tools.ietf.org/html/rfc6960#section-3.2
  // 5. The time at which the status being indicated is known to be
  //    correct (thisUpdate) is sufficiently recent;
  // 6. When available, the time at or before which newer information will
  //    be available about the status of the certificate (nextUpdate) is
  //    greater than the current time.

  Time thisUpdate(Time::uninitialized);
  rv = der::GeneralizedTime(input, thisUpdate);
  if (rv != Success) {
    return rv;
  }

  static const uint64_t SLOP_SECONDS = Time::ONE_DAY_IN_SECONDS;

  Time timePlusSlop(context.time);
  rv = timePlusSlop.AddSeconds(SLOP_SECONDS);
  if (rv != Success) {
    return rv;
  }
  if (thisUpdate > timePlusSlop) {
    return Result::ERROR_OCSP_FUTURE_RESPONSE;
  }

  Time notAfter(Time::uninitialized);
  static const uint8_t NEXT_UPDATE_TAG =
    der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 0;
  if (input.Peek(NEXT_UPDATE_TAG)) {
    Time nextUpdate(Time::uninitialized);
    rv = der::Nested(input, NEXT_UPDATE_TAG, [&nextUpdate](Reader& r) {
      return der::GeneralizedTime(r, nextUpdate);
    });
    if (rv != Success) {
      return rv;
    }

    if (nextUpdate < thisUpdate) {
      return Result::ERROR_OCSP_MALFORMED_RESPONSE;
    }
    notAfter = thisUpdate;
    if (notAfter.AddSeconds(context.maxLifetimeInDays *
                            Time::ONE_DAY_IN_SECONDS) != Success) {
      // This could only happen if we're dealing with times beyond the year
      // 10,000AD.
      return Result::ERROR_OCSP_FUTURE_RESPONSE;
    }
    if (nextUpdate <= notAfter) {
      notAfter = nextUpdate;
    }
  } else {
    // NSS requires all OCSP responses without a nextUpdate to be recent.
    // Match that stricter behavior.
    notAfter = thisUpdate;
    if (notAfter.AddSeconds(Time::ONE_DAY_IN_SECONDS) != Success) {
      // This could only happen if we're dealing with times beyond the year
      // 10,000AD.
      return Result::ERROR_OCSP_FUTURE_RESPONSE;
    }
  }

  // Add some slop to hopefully handle clock-skew.
  Time notAfterPlusSlop(notAfter);
  rv = notAfterPlusSlop.AddSeconds(SLOP_SECONDS);
  if (rv != Success) {
    // This could only happen if we're dealing with times beyond the year
    // 10,000AD.
    return Result::ERROR_OCSP_FUTURE_RESPONSE;
  }
  if (context.time > notAfterPlusSlop) {
    context.expired = true;
  }

  rv = der::OptionalExtensions(
    input,
    der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 1,
    [&context](Reader& extnID, const Input& extnValue, bool critical,
               /*out*/ bool& understood) {
      return RememberSingleExtension(context, extnID, extnValue, critical,
                                     understood);
    });

  if (rv != Success) {
    return rv;
  }

  if (context.thisUpdate) {
    *context.thisUpdate = thisUpdate;
  }
  if (context.validThrough) {
    *context.validThrough = notAfterPlusSlop;
  }

  return Success;
}

// CertID          ::=     SEQUENCE {
//        hashAlgorithm       AlgorithmIdentifier,
//        issuerNameHash      OCTET STRING, -- Hash of issuer's DN
//        issuerKeyHash       OCTET STRING, -- Hash of issuer's public key
//        serialNumber        CertificateSerialNumber }
static inline Result
CertID(Reader& input, const Context& context, /*out*/ bool& match)
{
  match = false;

  DigestAlgorithm hashAlgorithm;
  Result rv = der::DigestAlgorithmIdentifier(input, hashAlgorithm);
  if (rv != Success) {
    if (rv == Result::ERROR_INVALID_ALGORITHM) {
      // Skip entries that are hashed with algorithms we don't support.
      input.SkipToEnd();
      return Success;
    }
    return rv;
  }

  Input issuerNameHash;
  rv = der::ExpectTagAndGetValue(input, der::OCTET_STRING, issuerNameHash);
  if (rv != Success) {
    return rv;
  }

  Input issuerKeyHash;
  rv = der::ExpectTagAndGetValue(input, der::OCTET_STRING, issuerKeyHash);
  if (rv != Success) {
    return rv;
  }

  Input serialNumber;
  rv = der::CertificateSerialNumber(input, serialNumber);
  if (rv != Success) {
    return rv;
  }

  if (!InputsAreEqual(serialNumber, context.certID.serialNumber)) {
    // This does not reference the certificate we're interested in.
    // Consume the rest of the input and return successfully to
    // potentially continue processing other responses.
    input.SkipToEnd();
    return Success;
  }

  // TODO: support SHA-2 hashes.

  if (hashAlgorithm != DigestAlgorithm::sha1) {
    // Again, not interested in this response. Consume input, return success.
    input.SkipToEnd();
    return Success;
  }

  if (issuerNameHash.GetLength() != SHA1_DIGEST_LENGTH) {
    return Result::ERROR_OCSP_MALFORMED_RESPONSE;
  }

  // From http://tools.ietf.org/html/rfc6960#section-4.1.1:
  // "The hash shall be calculated over the DER encoding of the
  // issuer's name field in the certificate being checked."
  uint8_t hashBuf[SHA1_DIGEST_LENGTH];
  rv = context.trustDomain.DigestBuf(context.certID.issuer,
                                     DigestAlgorithm::sha1, hashBuf,
                                     sizeof(hashBuf));
  if (rv != Success) {
    return rv;
  }
  Input computed(hashBuf);
  if (!InputsAreEqual(computed, issuerNameHash)) {
    // Again, not interested in this response. Consume input, return success.
    input.SkipToEnd();
    return Success;
  }

  return MatchKeyHash(context.trustDomain, issuerKeyHash,
                      context.certID.issuerSubjectPublicKeyInfo, match);
}

// From http://tools.ietf.org/html/rfc6960#section-4.1.1:
// "The hash shall be calculated over the value (excluding tag and length) of
// the subject public key field in the issuer's certificate."
//
// From http://tools.ietf.org/html/rfc6960#appendix-B.1:
// KeyHash ::= OCTET STRING -- SHA-1 hash of responder's public key
//                          -- (i.e., the SHA-1 hash of the value of the
//                          -- BIT STRING subjectPublicKey [excluding
//                          -- the tag, length, and number of unused
//                          -- bits] in the responder's certificate)
static Result
MatchKeyHash(TrustDomain& trustDomain, Input keyHash,
             const Input subjectPublicKeyInfo, /*out*/ bool& match)
{
  if (keyHash.GetLength() != SHA1_DIGEST_LENGTH)  {
    return Result::ERROR_OCSP_MALFORMED_RESPONSE;
  }
  uint8_t hashBuf[SHA1_DIGEST_LENGTH];
  Result rv = KeyHash(trustDomain, subjectPublicKeyInfo, hashBuf,
                      sizeof hashBuf);
  if (rv != Success) {
    return rv;
  }
  Input computed(hashBuf);
  match = InputsAreEqual(computed, keyHash);
  return Success;
}

// TODO(bug 966856): support SHA-2 hashes
Result
KeyHash(TrustDomain& trustDomain, const Input subjectPublicKeyInfo,
        /*out*/ uint8_t* hashBuf, size_t hashBufSize)
{
  if (!hashBuf || hashBufSize != SHA1_DIGEST_LENGTH) {
    return Result::FATAL_ERROR_LIBRARY_FAILURE;
  }

  // RFC 5280 Section 4.1
  //
  // SubjectPublicKeyInfo  ::=  SEQUENCE  {
  //    algorithm            AlgorithmIdentifier,
  //    subjectPublicKey     BIT STRING  }

  Reader spki;
  Result rv = der::ExpectTagAndGetValueAtEnd(subjectPublicKeyInfo,
                                             der::SEQUENCE, spki);
  if (rv != Success) {
    return rv;
  }

  // Skip AlgorithmIdentifier
  rv = der::ExpectTagAndSkipValue(spki, der::SEQUENCE);
  if (rv != Success) {
    return rv;
  }

  Input subjectPublicKey;
  rv = der::BitStringWithNoUnusedBits(spki, subjectPublicKey);
  if (rv != Success) {
    return rv;
  }
  rv = der::End(spki);
  if (rv != Success) {
    return rv;
  }

  return trustDomain.DigestBuf(subjectPublicKey, DigestAlgorithm::sha1,
                               hashBuf, hashBufSize);
}

Result
ExtensionNotUnderstood(Reader& /*extnID*/, Input /*extnValue*/,
                       bool /*critical*/, /*out*/ bool& understood)
{
  understood = false;
  return Success;
}

Result
RememberSingleExtension(Context& context, Reader& extnID, Input extnValue,
                        bool /*critical*/, /*out*/ bool& understood)
{
  understood = false;

  // SingleExtension for Signed Certificate Timestamp List.
  // See Section 3.3 of RFC 6962.
  // python DottedOIDToCode.py
  //   id_ocsp_singleExtensionSctList 1.3.6.1.4.1.11129.2.4.5
  static const uint8_t id_ocsp_singleExtensionSctList[] = {
    0x2b, 0x06, 0x01, 0x04, 0x01, 0xd6, 0x79, 0x02, 0x04, 0x05
  };

  if (extnID.MatchRest(id_ocsp_singleExtensionSctList)) {
    // Empty values are not allowed for this extension. Note that
    // we assume this later, when checking if the extension was present.
    if (extnValue.GetLength() == 0) {
      return Result::ERROR_EXTENSION_VALUE_INVALID;
    }
    if (context.signedCertificateTimestamps.Init(extnValue) != Success) {
      // Duplicate extension.
      return Result::ERROR_EXTENSION_VALUE_INVALID;
    }
    understood = true;
  }

  return Success;
}

//   1. The certificate identified in a received response corresponds to
//      the certificate that was identified in the corresponding request;
//   2. The signature on the response is valid;
//   3. The identity of the signer matches the intended recipient of the
//      request;
//   4. The signer is currently authorized to provide a response for the
//      certificate in question;
//   5. The time at which the status being indicated is known to be
//      correct (thisUpdate) is sufficiently recent;
//   6. When available, the time at or before which newer information will
//      be available about the status of the certificate (nextUpdate) is
//      greater than the current time.
//
//   Responses whose nextUpdate value is earlier than
//   the local system time value SHOULD be considered unreliable.
//   Responses whose thisUpdate time is later than the local system time
//   SHOULD be considered unreliable.
//
//   If nextUpdate is not set, the responder is indicating that newer
//   revocation information is available all the time.
//
// http://tools.ietf.org/html/rfc5019#section-4

Result
CreateEncodedOCSPRequest(TrustDomain& trustDomain, const struct CertID& certID,
                         /*out*/ uint8_t (&out)[OCSP_REQUEST_MAX_LENGTH],
                         /*out*/ size_t& outLen)
{
  // We do not add any extensions to the request.

  // RFC 6960 says "An OCSP client MAY wish to specify the kinds of response
  // types it understands. To do so, it SHOULD use an extension with the OID
  // id-pkix-ocsp-response." This use of MAY and SHOULD is unclear. MSIE11
  // on Windows 8.1 does not include any extensions, whereas NSS has always
  // included the id-pkix-ocsp-response extension. Avoiding the sending the
  // extension is better for OCSP GET because it makes the request smaller,
  // and thus more likely to fit within the 255 byte limit for OCSP GET that
  // is specified in RFC 5019 Section 5.

  // Bug 966856: Add the id-pkix-ocsp-pref-sig-algs extension.

  // Since we don't know whether the OCSP responder supports anything other
  // than SHA-1, we have no choice but to use SHA-1 for issuerNameHash and
  // issuerKeyHash.
  static const uint8_t hashAlgorithm[11] = {
    0x30, 0x09,                               // SEQUENCE
    0x06, 0x05, 0x2B, 0x0E, 0x03, 0x02, 0x1A, //   OBJECT IDENTIFIER id-sha1
    0x05, 0x00,                               //   NULL
  };
  static const uint8_t hashLen = 160 / 8;

  static const unsigned int totalLenWithoutSerialNumberData
    = 2                             // OCSPRequest
    + 2                             //   tbsRequest
    + 2                             //     requestList
    + 2                             //       Request
    + 2                             //         reqCert (CertID)
    + sizeof(hashAlgorithm)         //           hashAlgorithm
    + 2 + hashLen                   //           issuerNameHash
    + 2 + hashLen                   //           issuerKeyHash
    + 2;                            //           serialNumber (header)

  // The only way we could have a request this large is if the serialNumber was
  // ridiculously and unreasonably large. RFC 5280 says "Conforming CAs MUST
  // NOT use serialNumber values longer than 20 octets." With this restriction,
  // we allow for some amount of non-conformance with that requirement while
  // still ensuring we can encode the length values in the ASN.1 TLV structures
  // in a single byte.
  static_assert(totalLenWithoutSerialNumberData < OCSP_REQUEST_MAX_LENGTH,
                "totalLenWithoutSerialNumberData too big");
  if (certID.serialNumber.GetLength() >
        OCSP_REQUEST_MAX_LENGTH - totalLenWithoutSerialNumberData) {
    return Result::ERROR_BAD_DER;
  }

  outLen = totalLenWithoutSerialNumberData + certID.serialNumber.GetLength();

  uint8_t totalLen = static_cast<uint8_t>(outLen);

  uint8_t* d = out;
  *d++ = 0x30; *d++ = totalLen - 2u;  // OCSPRequest (SEQUENCE)
  *d++ = 0x30; *d++ = totalLen - 4u;  //   tbsRequest (SEQUENCE)
  *d++ = 0x30; *d++ = totalLen - 6u;  //     requestList (SEQUENCE OF)
  *d++ = 0x30; *d++ = totalLen - 8u;  //       Request (SEQUENCE)
  *d++ = 0x30; *d++ = totalLen - 10u; //         reqCert (CertID SEQUENCE)

  // reqCert.hashAlgorithm
  for (size_t i = 0; i < sizeof(hashAlgorithm); ++i) {
    *d++ = hashAlgorithm[i];
  }

  // reqCert.issuerNameHash (OCTET STRING)
  *d++ = 0x04;
  *d++ = hashLen;
  Result rv = trustDomain.DigestBuf(certID.issuer, DigestAlgorithm::sha1, d,
                                    hashLen);
  if (rv != Success) {
    return rv;
  }
  d += hashLen;

  // reqCert.issuerKeyHash (OCTET STRING)
  *d++ = 0x04;
  *d++ = hashLen;
  rv = KeyHash(trustDomain, certID.issuerSubjectPublicKeyInfo, d, hashLen);
  if (rv != Success) {
    return rv;
  }
  d += hashLen;

  // reqCert.serialNumber (INTEGER)
  *d++ = 0x02; // INTEGER
  *d++ = static_cast<uint8_t>(certID.serialNumber.GetLength());
  Reader serialNumber(certID.serialNumber);
  do {
    rv = serialNumber.Read(*d);
    if (rv != Success) {
      return rv;
    }
    ++d;
  } while (!serialNumber.AtEnd());

  assert(d == out + totalLen);

  return Success;
}

} } // namespace mozilla::pkix