1// Copyright 2014 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "chrome/browser/metrics/variations/variations_seed_store.h"
6
7#include "base/base64.h"
8#include "base/metrics/histogram.h"
9#include "base/prefs/pref_registry_simple.h"
10#include "base/prefs/pref_service.h"
11#include "base/sha1.h"
12#include "base/strings/string_number_conversions.h"
13#include "chrome/common/pref_names.h"
14#include "components/variations/proto/variations_seed.pb.h"
15#include "crypto/signature_verifier.h"
16
17namespace chrome_variations {
18
19namespace {
20
21// Signature verification is disabled on mobile platforms for now, since it
22// adds about ~15ms to the startup time on mobile (vs. a couple ms on desktop).
23bool SignatureVerificationEnabled() {
24#if defined(OS_IOS) || defined(OS_ANDROID)
25  return false;
26#else
27  return true;
28#endif
29}
30
31// This is the algorithm ID for ECDSA with SHA-256. Parameters are ABSENT.
32// RFC 5758:
33//   ecdsa-with-SHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
34//        us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 2 }
35//   ...
36//   When the ecdsa-with-SHA224, ecdsa-with-SHA256, ecdsa-with-SHA384, or
37//   ecdsa-with-SHA512 algorithm identifier appears in the algorithm field
38//   as an AlgorithmIdentifier, the encoding MUST omit the parameters
39//   field.  That is, the AlgorithmIdentifier SHALL be a SEQUENCE of one
40//   component, the OID ecdsa-with-SHA224, ecdsa-with-SHA256, ecdsa-with-
41//   SHA384, or ecdsa-with-SHA512.
42// See also RFC 5480, Appendix A.
43const uint8 kECDSAWithSHA256AlgorithmID[] = {
44  0x30, 0x0a,
45    0x06, 0x08,
46      0x2a, 0x86, 0x48, 0xce, 0x3d, 0x04, 0x03, 0x02,
47};
48
49// The ECDSA public key of the variations server for verifying variations seed
50// signatures.
51const uint8_t kPublicKey[] = {
52  0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01,
53  0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00,
54  0x04, 0x51, 0x7c, 0x31, 0x4b, 0x50, 0x42, 0xdd, 0x59, 0xda, 0x0b, 0xfa, 0x43,
55  0x44, 0x33, 0x7c, 0x5f, 0xa1, 0x0b, 0xd5, 0x82, 0xf6, 0xac, 0x04, 0x19, 0x72,
56  0x6c, 0x40, 0xd4, 0x3e, 0x56, 0xe2, 0xa0, 0x80, 0xa0, 0x41, 0xb3, 0x23, 0x7b,
57  0x71, 0xc9, 0x80, 0x87, 0xde, 0x35, 0x0d, 0x25, 0x71, 0x09, 0x7f, 0xb4, 0x15,
58  0x2b, 0xff, 0x82, 0x4d, 0xd3, 0xfe, 0xc5, 0xef, 0x20, 0xc6, 0xa3, 0x10, 0xbf,
59};
60
61// Note: UMA histogram enum - don't re-order or remove entries.
62enum VariationSeedEmptyState {
63  VARIATIONS_SEED_NOT_EMPTY,
64  VARIATIONS_SEED_EMPTY,
65  VARIATIONS_SEED_CORRUPT,
66  VARIATIONS_SEED_INVALID_SIGNATURE,
67  VARIATIONS_SEED_EMPTY_ENUM_SIZE,
68};
69
70void RecordVariationSeedEmptyHistogram(VariationSeedEmptyState state) {
71  UMA_HISTOGRAM_ENUMERATION("Variations.SeedEmpty", state,
72                            VARIATIONS_SEED_EMPTY_ENUM_SIZE);
73}
74
75// Note: UMA histogram enum - don't re-order or remove entries.
76enum VariationsSeedDateChangeState {
77  SEED_DATE_NO_OLD_DATE,
78  SEED_DATE_NEW_DATE_OLDER,
79  SEED_DATE_SAME_DAY,
80  SEED_DATE_NEW_DAY,
81  SEED_DATE_ENUM_SIZE,
82};
83
84// Truncates a time to the start of the day in UTC. If given a time representing
85// 2014-03-11 10:18:03.1 UTC, it will return a time representing
86// 2014-03-11 00:00:00.0 UTC.
87base::Time TruncateToUTCDay(const base::Time& time) {
88  base::Time::Exploded exploded;
89  time.UTCExplode(&exploded);
90  exploded.hour = 0;
91  exploded.minute = 0;
92  exploded.second = 0;
93  exploded.millisecond = 0;
94
95  return base::Time::FromUTCExploded(exploded);
96}
97
98VariationsSeedDateChangeState GetSeedDateChangeState(
99    const base::Time& server_seed_date,
100    const base::Time& stored_seed_date) {
101  if (server_seed_date < stored_seed_date)
102    return SEED_DATE_NEW_DATE_OLDER;
103
104  if (TruncateToUTCDay(server_seed_date) !=
105      TruncateToUTCDay(stored_seed_date)) {
106    // The server date is earlier than the stored date, and they are from
107    // different UTC days, so |server_seed_date| is a valid new day.
108    return SEED_DATE_NEW_DAY;
109  }
110  return SEED_DATE_SAME_DAY;
111}
112
113}  // namespace
114
115VariationsSeedStore::VariationsSeedStore(PrefService* local_state)
116    : local_state_(local_state) {
117}
118
119VariationsSeedStore::~VariationsSeedStore() {
120}
121
122bool VariationsSeedStore::LoadSeed(variations::VariationsSeed* seed) {
123  const std::string base64_seed_data =
124      local_state_->GetString(prefs::kVariationsSeed);
125  if (base64_seed_data.empty()) {
126    RecordVariationSeedEmptyHistogram(VARIATIONS_SEED_EMPTY);
127    return false;
128  }
129
130  // If the decode process fails, assume the pref value is corrupt and clear it.
131  std::string seed_data;
132  if (!base::Base64Decode(base64_seed_data, &seed_data) ||
133      !seed->ParseFromString(seed_data)) {
134    VLOG(1) << "Variations seed data in local pref is corrupt, clearing the "
135            << "pref.";
136    ClearPrefs();
137    RecordVariationSeedEmptyHistogram(VARIATIONS_SEED_CORRUPT);
138    return false;
139  }
140
141  const std::string base64_seed_signature =
142      local_state_->GetString(prefs::kVariationsSeedSignature);
143  const VerifySignatureResult result =
144      VerifySeedSignature(seed_data, base64_seed_signature);
145  if (result != VARIATIONS_SEED_SIGNATURE_ENUM_SIZE) {
146    UMA_HISTOGRAM_ENUMERATION("Variations.LoadSeedSignature", result,
147                              VARIATIONS_SEED_SIGNATURE_ENUM_SIZE);
148    if (result != VARIATIONS_SEED_SIGNATURE_VALID) {
149      VLOG(1) << "Variations seed signature in local pref missing or invalid "
150              << "with result: " << result << ". Clearing the pref.";
151      ClearPrefs();
152      RecordVariationSeedEmptyHistogram(VARIATIONS_SEED_INVALID_SIGNATURE);
153      return false;
154    }
155  }
156
157  variations_serial_number_ = seed->serial_number();
158  RecordVariationSeedEmptyHistogram(VARIATIONS_SEED_NOT_EMPTY);
159  return true;
160}
161
162bool VariationsSeedStore::StoreSeedData(
163    const std::string& seed_data,
164    const std::string& base64_seed_signature,
165    const base::Time& date_fetched,
166    variations::VariationsSeed* parsed_seed) {
167  if (seed_data.empty()) {
168    VLOG(1) << "Variations seed data is empty, rejecting the seed.";
169    return false;
170  }
171
172  // Only store the seed data if it parses correctly.
173  variations::VariationsSeed seed;
174  if (!seed.ParseFromString(seed_data)) {
175    VLOG(1) << "Variations seed data is not in valid proto format, "
176            << "rejecting the seed.";
177    return false;
178  }
179
180  const VerifySignatureResult result =
181      VerifySeedSignature(seed_data, base64_seed_signature);
182  if (result != VARIATIONS_SEED_SIGNATURE_ENUM_SIZE) {
183    UMA_HISTOGRAM_ENUMERATION("Variations.StoreSeedSignature", result,
184                              VARIATIONS_SEED_SIGNATURE_ENUM_SIZE);
185    if (result != VARIATIONS_SEED_SIGNATURE_VALID) {
186      VLOG(1) << "Variations seed signature missing or invalid with result: "
187              << result << ". Rejecting the seed.";
188      return false;
189    }
190  }
191
192  std::string base64_seed_data;
193  base::Base64Encode(seed_data, &base64_seed_data);
194
195  // TODO(asvitkine): This pref is no longer being used. Remove it completely
196  // in a couple of releases.
197  local_state_->ClearPref(prefs::kVariationsSeedHash);
198
199  local_state_->SetString(prefs::kVariationsSeed, base64_seed_data);
200  UpdateSeedDateAndLogDayChange(date_fetched);
201  local_state_->SetString(prefs::kVariationsSeedSignature,
202                          base64_seed_signature);
203  variations_serial_number_ = seed.serial_number();
204  if (parsed_seed)
205    seed.Swap(parsed_seed);
206
207  return true;
208}
209
210void VariationsSeedStore::UpdateSeedDateAndLogDayChange(
211    const base::Time& server_date_fetched) {
212  VariationsSeedDateChangeState date_change = SEED_DATE_NO_OLD_DATE;
213
214  if (local_state_->HasPrefPath(prefs::kVariationsSeedDate)) {
215    const int64 stored_date_value =
216        local_state_->GetInt64(prefs::kVariationsSeedDate);
217    const base::Time stored_date =
218        base::Time::FromInternalValue(stored_date_value);
219
220    date_change = GetSeedDateChangeState(server_date_fetched, stored_date);
221  }
222
223  UMA_HISTOGRAM_ENUMERATION("Variations.SeedDateChange", date_change,
224                            SEED_DATE_ENUM_SIZE);
225
226  local_state_->SetInt64(prefs::kVariationsSeedDate,
227                         server_date_fetched.ToInternalValue());
228}
229
230// static
231void VariationsSeedStore::RegisterPrefs(PrefRegistrySimple* registry) {
232  registry->RegisterStringPref(prefs::kVariationsSeed, std::string());
233  registry->RegisterStringPref(prefs::kVariationsSeedHash, std::string());
234  registry->RegisterInt64Pref(prefs::kVariationsSeedDate,
235                              base::Time().ToInternalValue());
236  registry->RegisterStringPref(prefs::kVariationsSeedSignature, std::string());
237}
238
239void VariationsSeedStore::ClearPrefs() {
240  local_state_->ClearPref(prefs::kVariationsSeed);
241  local_state_->ClearPref(prefs::kVariationsSeedDate);
242  local_state_->ClearPref(prefs::kVariationsSeedHash);
243  local_state_->ClearPref(prefs::kVariationsSeedSignature);
244}
245
246VariationsSeedStore::VerifySignatureResult
247VariationsSeedStore::VerifySeedSignature(
248    const std::string& seed_bytes,
249    const std::string& base64_seed_signature) {
250  if (!SignatureVerificationEnabled())
251    return VARIATIONS_SEED_SIGNATURE_ENUM_SIZE;
252
253  if (base64_seed_signature.empty())
254    return VARIATIONS_SEED_SIGNATURE_MISSING;
255
256  std::string signature;
257  if (!base::Base64Decode(base64_seed_signature, &signature))
258    return VARIATIONS_SEED_SIGNATURE_DECODE_FAILED;
259
260  crypto::SignatureVerifier verifier;
261  if (!verifier.VerifyInit(
262          kECDSAWithSHA256AlgorithmID, sizeof(kECDSAWithSHA256AlgorithmID),
263          reinterpret_cast<const uint8*>(signature.data()), signature.size(),
264          kPublicKey, arraysize(kPublicKey))) {
265    return VARIATIONS_SEED_SIGNATURE_INVALID_SIGNATURE;
266  }
267
268  verifier.VerifyUpdate(reinterpret_cast<const uint8*>(seed_bytes.data()),
269                        seed_bytes.size());
270  if (verifier.VerifyFinal())
271    return VARIATIONS_SEED_SIGNATURE_VALID;
272  return VARIATIONS_SEED_SIGNATURE_INVALID_SEED;
273}
274
275}  // namespace chrome_variations
276