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// Copyright 2019 The Chromium Authors
// 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/logging.h"
#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 "components/metrics/structured/histogram_util.h"
#include "crypto/hmac.h"
#include "crypto/sha2.h"
namespace metrics {
namespace structured {
namespace {
// The expected size of a key, in bytes.
constexpr size_t kKeySize = 32;
// 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));
}
} // namespace
KeyData::KeyData(const base::FilePath& path,
const base::TimeDelta& save_delay,
base::OnceCallback<void()> on_initialized)
: on_initialized_(std::move(on_initialized)) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
proto_ = std::make_unique<PersistentProto<KeyDataProto>>(
path, save_delay,
base::BindOnce(&KeyData::OnRead, weak_factory_.GetWeakPtr()),
base::BindRepeating(&KeyData::OnWrite, weak_factory_.GetWeakPtr()));
}
KeyData::~KeyData() = default;
void KeyData::OnRead(const ReadStatus status) {
is_initialized_ = true;
switch (status) {
case ReadStatus::kOk:
case ReadStatus::kMissing:
break;
case ReadStatus::kReadError:
LogInternalError(StructuredMetricsError::kKeyReadError);
break;
case ReadStatus::kParseError:
LogInternalError(StructuredMetricsError::kKeyParseError);
break;
}
std::move(on_initialized_).Run();
}
void KeyData::OnWrite(const WriteStatus status) {
switch (status) {
case WriteStatus::kOk:
break;
case WriteStatus::kWriteError:
LogInternalError(StructuredMetricsError::kKeyWriteError);
break;
case WriteStatus::kSerializationError:
LogInternalError(StructuredMetricsError::kKeySerializationError);
break;
}
}
void KeyData::WriteNowForTest() {
proto_.get()->StartWrite();
}
//---------------
// Key management
//---------------
absl::optional<std::string> KeyData::ValidateAndGetKey(
const uint64_t project_name_hash,
int key_rotation_period) {
if (!is_initialized_) {
NOTREACHED();
return absl::nullopt;
}
const int now = (base::Time::Now() - base::Time::UnixEpoch()).InDays();
KeyProto& key = (*(proto_.get()->get()->mutable_keys()))[project_name_hash];
// Generate or rotate key.
const int last_rotation = key.last_rotation();
if (key.key().empty() || last_rotation == 0) {
LogKeyValidation(KeyValidationState::kCreated);
// If the key is empty, generate a new one. Set the last rotation to a
// uniformly selected day between today and |key_rotation_period| days
// ago, to uniformly distribute users amongst rotation cohorts.
const int rotation_seed = base::RandInt(0, key_rotation_period - 1);
UpdateKey(&key, now - rotation_seed, key_rotation_period);
} else if (now - last_rotation > key_rotation_period) {
LogKeyValidation(KeyValidationState::kRotated);
// If the key is outdated, generate a new one. Update the last rotation
// such that the user stays in the same cohort.
//
// Note that if the max key rotation period has changed, the new rotation
// period will be used to calculate whether the key should be rotated or
// not.
const int new_last_rotation =
now - (now - last_rotation) % key_rotation_period;
UpdateKey(&key, new_last_rotation, key_rotation_period);
} else {
LogKeyValidation(KeyValidationState::kValid);
}
// Return the key unless it's the wrong size, in which case return nullopt.
const std::string key_string = key.key();
if (key_string.size() != kKeySize) {
LogInternalError(StructuredMetricsError::kWrongKeyLength);
return absl::nullopt;
}
return key_string;
}
void KeyData::UpdateKey(KeyProto* key,
int last_key_rotation,
int key_rotation_period) {
key->set_key(GenerateKey());
key->set_last_rotation(last_key_rotation);
key->set_rotation_period(key_rotation_period);
proto_->QueueWrite();
}
//----------------
// IDs and hashing
//----------------
uint64_t KeyData::Id(const uint64_t project_name_hash,
int key_rotation_period) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
// Retrieve the key for |project_name_hash|.
const absl::optional<std::string> key =
ValidateAndGetKey(project_name_hash, key_rotation_period);
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::HmacMetric(const uint64_t project_name_hash,
const uint64_t metric_name_hash,
const std::string& value,
int key_rotation_period) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
// Retrieve the key for |project_name_hash|.
const absl::optional<std::string> key =
ValidateAndGetKey(project_name_hash, key_rotation_period);
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_name_hash), value});
uint64_t digest;
CHECK(hmac.Sign(salted_value, reinterpret_cast<uint8_t*>(&digest),
sizeof(digest)));
return digest;
}
//-----
// Misc
//-----
absl::optional<int> KeyData::LastKeyRotation(const uint64_t project_name_hash) {
const auto& keys = proto_.get()->get()->keys();
const auto& it = keys.find(project_name_hash);
if (it != keys.end()) {
return it->second.last_rotation();
}
return absl::nullopt;
}
void KeyData::Purge() {
proto_->Purge();
}
} // namespace structured
} // namespace metrics
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