1 // Copyright 2013 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.
5 #include "chrome/browser/prefs/pref_hash_calculator.h"
9 #include "base/json/json_string_value_serializer.h"
10 #include "base/logging.h"
11 #include "base/memory/scoped_ptr.h"
12 #include "base/strings/string_number_conversions.h"
13 #include "base/strings/string_util.h"
14 #include "base/values.h"
15 #include "crypto/hmac.h"
19 // Calculates an HMAC of |message| using |key|, encoded as a hexadecimal string.
20 std::string GetDigestString(const std::string& key,
21 const std::string& message) {
22 crypto::HMAC hmac(crypto::HMAC::SHA256);
23 std::vector<uint8> digest(hmac.DigestLength());
24 if (!hmac.Init(key) || !hmac.Sign(message, &digest[0], digest.size())) {
28 return base::HexEncode(&digest[0], digest.size());
31 // Verifies that |digest_string| is a valid HMAC of |message| using |key|.
32 // |digest_string| must be encoded as a hexadecimal string.
33 bool VerifyDigestString(const std::string& key,
34 const std::string& message,
35 const std::string& digest_string) {
36 crypto::HMAC hmac(crypto::HMAC::SHA256);
37 std::vector<uint8> digest;
38 return base::HexStringToBytes(digest_string, &digest) &&
41 base::StringPiece(reinterpret_cast<char*>(&digest[0]),
45 // Renders |value| as a string. |value| may be NULL, in which case the result
46 // is an empty string. This method can be expensive and its result should be
47 // re-used rather than recomputed where possible.
48 std::string ValueAsString(const base::Value* value) {
49 // Dictionary values may contain empty lists and sub-dictionaries. Make a
50 // deep copy with those removed to make the hash more stable.
51 const base::DictionaryValue* dict_value;
52 scoped_ptr<base::DictionaryValue> canonical_dict_value;
53 if (value && value->GetAsDictionary(&dict_value)) {
54 canonical_dict_value.reset(dict_value->DeepCopyWithoutEmptyChildren());
55 value = canonical_dict_value.get();
58 std::string value_as_string;
60 JSONStringValueSerializer serializer(&value_as_string);
61 serializer.Serialize(*value);
64 return value_as_string;
67 // Common helper for all hash algorithms.
68 std::string GetMessageFromValueAndComponents(
69 const std::string& value_as_string,
70 const std::vector<std::string>& extra_components) {
71 return JoinString(extra_components, "") + value_as_string;
75 // Generates a device ID based on the input device ID. The derived device ID has
76 // no useful properties beyond those of the input device ID except that it is
77 // consistent with previous implementations.
78 std::string GenerateDeviceIdLikePrefMetricsServiceDid(
79 const std::string& original_device_id) {
80 if (original_device_id.empty())
82 return StringToLowerASCII(
83 GetDigestString(original_device_id, "PrefMetricsService"));
86 // Verifies a hash using a deprecated hash algorithm. For validating old
87 // hashes during migration.
88 bool VerifyLegacyHash(const std::string& seed,
89 const std::string& value_as_string,
90 const std::string& digest_string) {
91 return VerifyDigestString(
93 GetMessageFromValueAndComponents(value_as_string,
94 std::vector<std::string>()),
100 PrefHashCalculator::PrefHashCalculator(const std::string& seed,
101 const std::string& device_id)
103 device_id_(GenerateDeviceIdLikePrefMetricsServiceDid(device_id)) {}
105 std::string PrefHashCalculator::Calculate(const std::string& path,
106 const base::Value* value) const {
107 return GetDigestString(seed_, GetMessage(path, ValueAsString(value)));
110 PrefHashCalculator::ValidationResult PrefHashCalculator::Validate(
111 const std::string& path,
112 const base::Value* value,
113 const std::string& digest_string) const {
114 const std::string value_as_string(ValueAsString(value));
115 if (VerifyDigestString(seed_, GetMessage(path, value_as_string),
119 if (VerifyLegacyHash(seed_, value_as_string, digest_string))
124 std::string PrefHashCalculator::GetMessage(
125 const std::string& path,
126 const std::string& value_as_string) const {
127 std::vector<std::string> components;
128 if (!device_id_.empty())
129 components.push_back(device_id_);
130 components.push_back(path);
131 return GetMessageFromValueAndComponents(value_as_string, components);