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// Copyright 2022 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/browsing_topics/util.h"
#include <algorithm>
#include "base/lazy_instance.h"
#include "base/rand_util.h"
#include "crypto/hmac.h"
#include "crypto/sha2.h"
#include "third_party/blink/public/common/features.h"
namespace browsing_topics {
namespace {
// Note that updating the use case prefixes below will change the pre-existing
// per-user stickiness. Some of the derived data may already have been persisted
// elsewhere. Be sure you are aware of the implications before updating those
// strings. Note also that the version here is just about the hash method, and
// is distinctive from the broader configuration version of the Topics API.
const char kRandomOrTopTopicDecisionPrefix[] =
"TopicsV1_RandomOrTopTopicDecision|";
const char kRandomTopicIndexDecisionPrefix[] =
"TopicsV1_RandomTopicIndexDecision|";
const char kTopTopicIndexDecisionPrefix[] = "TopicsV1_TopTopicIndexDecision|";
const char kEpochSwitchTimeDecisionPrefix[] =
"TopicsV1_EpochSwitchTimeDecision|";
const char kContextDomainStoragePrefix[] = "TopicsV1_ContextDomainStorage|";
const char kMainFrameHostStoragePrefix[] = "TopicsV1_MainFrameHostStorage|";
uint64_t HmacHash(ReadOnlyHmacKey hmac_key,
const std::string& use_case_prefix,
const std::string& data) {
crypto::HMAC hmac(crypto::HMAC::SHA256);
CHECK(hmac.Init(hmac_key));
uint64_t result;
CHECK(hmac.Sign(use_case_prefix + data,
reinterpret_cast<unsigned char*>(&result), sizeof(result)));
return result;
}
base::LazyInstance<browsing_topics::HmacKey>::Leaky
g_hmac_key_override_for_testing;
} // namespace
absl::optional<size_t> GetTaxonomySize() {
if (blink::features::kBrowsingTopicsTaxonomyVersion.Get() == 1) {
// Taxonomy version 1 has 349 topics.
// https://github.com/jkarlin/topics/blob/main/taxonomy_v1.md
return 349;
}
return absl::nullopt;
}
HmacKey GenerateRandomHmacKey() {
if (g_hmac_key_override_for_testing.IsCreated())
return g_hmac_key_override_for_testing.Get();
HmacKey result = {};
base::RandBytes(result.data(), result.size());
return result;
}
uint64_t HashTopDomainForRandomOrTopTopicDecision(
ReadOnlyHmacKey hmac_key,
base::Time epoch_calculation_time,
const std::string& top_domain) {
int64_t time_microseconds =
epoch_calculation_time.ToDeltaSinceWindowsEpoch().InMicroseconds();
std::string epoch_id(reinterpret_cast<const char*>(&time_microseconds),
sizeof(time_microseconds));
return HmacHash(hmac_key, kRandomOrTopTopicDecisionPrefix,
epoch_id + top_domain);
}
uint64_t HashTopDomainForRandomTopicIndexDecision(
ReadOnlyHmacKey hmac_key,
base::Time epoch_calculation_time,
const std::string& top_domain) {
int64_t time_microseconds =
epoch_calculation_time.ToDeltaSinceWindowsEpoch().InMicroseconds();
std::string epoch_id(reinterpret_cast<const char*>(&time_microseconds),
sizeof(time_microseconds));
return HmacHash(hmac_key, kRandomTopicIndexDecisionPrefix,
epoch_id + top_domain);
}
uint64_t HashTopDomainForTopTopicIndexDecision(
ReadOnlyHmacKey hmac_key,
base::Time epoch_calculation_time,
const std::string& top_domain) {
int64_t time_microseconds =
epoch_calculation_time.ToDeltaSinceWindowsEpoch().InMicroseconds();
std::string epoch_id(reinterpret_cast<const char*>(&time_microseconds),
sizeof(time_microseconds));
return HmacHash(hmac_key, kTopTopicIndexDecisionPrefix,
epoch_id + top_domain);
}
uint64_t HashTopDomainForEpochSwitchTimeDecision(
ReadOnlyHmacKey hmac_key,
const std::string& top_domain) {
return HmacHash(hmac_key, kEpochSwitchTimeDecisionPrefix, top_domain);
}
HashedDomain HashContextDomainForStorage(ReadOnlyHmacKey hmac_key,
const std::string& context_domain) {
return HashedDomain(
HmacHash(hmac_key, kContextDomainStoragePrefix, context_domain));
}
HashedHost HashMainFrameHostForStorage(const std::string& main_frame_host) {
int64_t result;
crypto::SHA256HashString(kMainFrameHostStoragePrefix + main_frame_host,
&result, sizeof(result));
return HashedHost(result);
}
base::Time DeriveHistoryDataStartTime(base::Time calculation_time,
base::Time data_accessible_since) {
return std::max(data_accessible_since,
calculation_time -
blink::features::kBrowsingTopicsTimePeriodPerEpoch.Get());
}
base::Time DeriveApiUsageContextDataStartTime(
base::Time calculation_time,
base::Time data_accessible_since) {
return std::max(
data_accessible_since,
calculation_time -
blink::features::
kBrowsingTopicsNumberOfEpochsOfObservationDataToUseForFiltering
.Get() *
blink::features::kBrowsingTopicsTimePeriodPerEpoch.Get());
}
void OverrideHmacKeyForTesting(ReadOnlyHmacKey hmac_key) {
std::copy(hmac_key.begin(), hmac_key.end(),
g_hmac_key_override_for_testing.Get().begin());
}
} // namespace browsing_topics
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