chrome/browser/prefs/pref_hash_calculator.cc

   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.
   4
   5 #include "chrome/browser/prefs/pref_hash_calculator.h"
   6
   7 #include <vector>
   8
   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"
  16
  17 namespace {
  18
  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())) {
  25     NOTREACHED();
  26     return std::string();
  27   }
  28   return base::HexEncode(&digest[0], digest.size());
  29 }
  30
  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) &&
  39       hmac.Init(key) &&
  40       hmac.Verify(message,
  41                   base::StringPiece(reinterpret_cast<char*>(&digest[0]),
  42                                     digest.size()));
  43 }
  44
  45 // Renders |value| as a string. |value| may be NULL, in which case the result
  46 // is an empty string.
  47 std::string ValueAsString(const base::Value* value) {
  48   // Dictionary values may contain empty lists and sub-dictionaries. Make a
  49   // deep copy with those removed to make the hash more stable.
  50   const base::DictionaryValue* dict_value;
  51   scoped_ptr<base::DictionaryValue> canonical_dict_value;
  52   if (value && value->GetAsDictionary(&dict_value)) {
  53     canonical_dict_value.reset(dict_value->DeepCopyWithoutEmptyChildren());
  54     value = canonical_dict_value.get();
  55   }
  56
  57   std::string value_as_string;
  58   if (value) {
  59     JSONStringValueSerializer serializer(&value_as_string);
  60     serializer.Serialize(*value);
  61   }
  62
  63   return value_as_string;
  64 }
  65
  66 // Common helper for all hash algorithms.
  67 std::string GetMessageFromValueAndComponents(
  68     const base::Value* value,
  69     const std::vector<std::string>& extra_components) {
  70   return JoinString(extra_components, "") + ValueAsString(value);
  71 }
  72
  73
  74 // Generates a device ID based on the input device ID. The derived device ID has
  75 // no useful properties beyond those of the input device ID except that it is
  76 // consistent with previous implementations.
  77 std::string GenerateDeviceIdLikePrefMetricsServiceDid(
  78     const std::string& original_device_id) {
  79   if (original_device_id.empty())
  80     return std::string();
  81   return StringToLowerASCII(
  82       GetDigestString(original_device_id, "PrefMetricsService"));
  83 }
  84
  85 // Verifies a hash using a deprecated hash algorithm. For validating old
  86 // hashes during migration.
  87 bool VerifyLegacyHash(const std::string& seed,
  88                       const base::Value* value,
  89                       const std::string& digest_string) {
  90   return VerifyDigestString(
  91       seed,
  92       GetMessageFromValueAndComponents(value, std::vector<std::string>()),
  93       digest_string);
  94 }
  95
  96 }  // namespace
  97
  98 PrefHashCalculator::PrefHashCalculator(const std::string& seed,
  99                                        const std::string& device_id)
 100     : seed_(seed),
 101       device_id_(GenerateDeviceIdLikePrefMetricsServiceDid(device_id)) {}
 102
 103 std::string PrefHashCalculator::Calculate(const std::string& path,
 104                                           const base::Value* value) const {
 105   return GetDigestString(seed_, GetMessage(path, value));
 106 }
 107
 108 PrefHashCalculator::ValidationResult PrefHashCalculator::Validate(
 109     const std::string& path,
 110     const base::Value* value,
 111     const std::string& digest_string) const {
 112   if (VerifyDigestString(seed_, GetMessage(path, value), digest_string))
 113     return VALID;
 114   if (VerifyLegacyHash(seed_, value, digest_string))
 115     return VALID_LEGACY;
 116   return INVALID;
 117 }
 118
 119 std::string PrefHashCalculator::GetMessage(const std::string& path,
 120                                            const base::Value* value) const {
 121   std::vector<std::string> components;
 122   if (!device_id_.empty())
 123     components.push_back(device_id_);
 124   components.push_back(path);
 125   return GetMessageFromValueAndComponents(value, components);
 126 }