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// Copyright 2019 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/metrics/structured/key_data.h"
#include <memory>
#include "base/rand_util.h"
#include "base/strings/strcat.h"
#include "base/strings/string_number_conversions.h"
#include "base/time/time.h"
#include "base/unguessable_token.h"
#include "base/values.h"
#include "components/metrics/structured/histogram_util.h"
#include "components/metrics/structured/structured_events.h"
#include "components/prefs/json_pref_store.h"
#include "crypto/hmac.h"
#include "crypto/sha2.h"
namespace metrics {
namespace structured {
namespace internal {
namespace {
// The expected size of a key, in bytes.
constexpr size_t kKeySize = 32;
// The default maximum number of days before rotating keys.
constexpr size_t kDefaultRotationPeriod = 90;
// Generates a key, which is the string representation of
// base::UnguessableToken, and is of size |kKeySize| bytes.
std::string GenerateKey() {
const std::string key = base::UnguessableToken::Create().ToString();
DCHECK_EQ(key.size(), kKeySize);
return key;
}
std::string HashToHex(const uint64_t hash) {
return base::HexEncode(&hash, sizeof(uint64_t));
}
std::string KeyPath(const uint64_t event) {
return base::StrCat({"keys.", base::NumberToString(event), ".key"});
}
std::string LastRotationPath(const uint64_t event) {
return base::StrCat({"keys.", base::NumberToString(event), ".last_rotation"});
}
std::string RotationPeriodPath(const uint64_t event) {
return base::StrCat(
{"keys.", base::NumberToString(event), ".rotation_period"});
}
} // namespace
KeyData::KeyData(JsonPrefStore* key_store) : key_store_(key_store) {
DCHECK(key_store_);
ValidateKeys();
}
KeyData::~KeyData() = default;
base::Optional<std::string> KeyData::ValidateAndGetKey(
const uint64_t project_name_hash) {
DCHECK(key_store_);
const int now = (base::Time::Now() - base::Time::UnixEpoch()).InDays();
bool key_is_valid = true;
// If the key for |project_name_hash| doesn't exist, initialize new key data.
// Set the last rotation to a uniformly selected day between today and
// |kDefaultRotationPeriod| days ago, to uniformly distribute users amongst
// rotation cohorts.
if (!key_store_->GetValue(KeyPath(project_name_hash), nullptr)) {
const int rotation_seed = base::RandInt(0, kDefaultRotationPeriod - 1);
SetRotationPeriod(project_name_hash, kDefaultRotationPeriod);
SetLastRotation(project_name_hash, now - rotation_seed);
SetKey(project_name_hash, GenerateKey());
LogKeyValidation(KeyValidationState::kCreated);
key_is_valid = false;
}
// If the key for |project_name_hash| is outdated, generate a new key and
// write it to the |keys| pref store along with updated rotation data. Update
// the last rotation such that the user stays in the same cohort.
const int rotation_period = GetRotationPeriod(project_name_hash);
const int last_rotation = GetLastRotation(project_name_hash);
if (now - last_rotation > rotation_period) {
const int new_last_rotation = now - (now - last_rotation) % rotation_period;
SetLastRotation(project_name_hash, new_last_rotation);
SetKey(project_name_hash, GenerateKey());
LogKeyValidation(KeyValidationState::kRotated);
key_is_valid = false;
}
if (key_is_valid) {
LogKeyValidation(KeyValidationState::kValid);
}
const base::Value* key_json;
if (!(key_store_->GetValue(KeyPath(project_name_hash), &key_json) &&
key_json->is_string())) {
LogInternalError(StructuredMetricsError::kMissingKey);
return base::nullopt;
}
const std::string key = key_json->GetString();
if (key.size() != kKeySize) {
LogInternalError(StructuredMetricsError::kWrongKeyLength);
return base::nullopt;
}
return key;
}
void KeyData::ValidateKeys() {
for (const uint64_t project_name_hash :
metrics::structured::events::kProjectNameHashes) {
ValidateAndGetKey(project_name_hash);
}
}
void KeyData::SetLastRotation(const uint64_t event, const int last_rotation) {
return key_store_->SetValue(LastRotationPath(event),
std::make_unique<base::Value>(last_rotation),
WriteablePrefStore::DEFAULT_PREF_WRITE_FLAGS);
}
void KeyData::SetRotationPeriod(const uint64_t event,
const int rotation_period) {
return key_store_->SetValue(RotationPeriodPath(event),
std::make_unique<base::Value>(rotation_period),
WriteablePrefStore::DEFAULT_PREF_WRITE_FLAGS);
}
void KeyData::SetKey(const uint64_t project_name_hash, const std::string& key) {
return key_store_->SetValue(KeyPath(project_name_hash),
std::make_unique<base::Value>(key),
WriteablePrefStore::DEFAULT_PREF_WRITE_FLAGS);
}
int KeyData::GetLastRotation(const uint64_t event) {
const base::Value* value;
if (!(key_store_->GetValue(LastRotationPath(event), &value) &&
value->is_int())) {
LogInternalError(StructuredMetricsError::kMissingLastRotation);
NOTREACHED();
return 0u;
}
return value->GetInt();
}
int KeyData::GetRotationPeriod(const uint64_t event) {
const base::Value* value;
if (!(key_store_->GetValue(RotationPeriodPath(event), &value) &&
value->is_int())) {
LogInternalError(StructuredMetricsError::kMissingRotationPeriod);
NOTREACHED();
return 0u;
}
return value->GetInt();
}
uint64_t KeyData::UserEventId(const uint64_t project_name_hash) {
// Retrieve the key for |event|.
const base::Optional<std::string> key = ValidateAndGetKey(project_name_hash);
if (!key) {
NOTREACHED();
return 0u;
}
// Compute and return the hash.
uint64_t hash;
crypto::SHA256HashString(key.value(), &hash, sizeof(uint64_t));
return hash;
}
uint64_t KeyData::HashForEventMetric(const uint64_t project_name_hash,
const uint64_t metric,
const std::string& value) {
// Retrieve the key for |project_name_hash|.
const base::Optional<std::string> key = ValidateAndGetKey(project_name_hash);
if (!key) {
NOTREACHED();
return 0u;
}
// Initialize the HMAC.
crypto::HMAC hmac(crypto::HMAC::HashAlgorithm::SHA256);
CHECK(hmac.Init(key.value()));
// Compute and return the digest.
const std::string salted_value = base::StrCat({HashToHex(metric), value});
uint64_t digest;
CHECK(hmac.Sign(salted_value, reinterpret_cast<uint8_t*>(&digest),
sizeof(digest)));
return digest;
}
} // namespace internal
} // namespace structured
} // namespace metrics
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