chrome/browser/prefs/pref_hash_calculator.h

   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 #ifndef CHROME_BROWSER_PREFS_PREF_HASH_CALCULATOR_H_
   6 #define CHROME_BROWSER_PREFS_PREF_HASH_CALCULATOR_H_
   7
   8 #include <string>
   9
  10 #include "base/basictypes.h"
  11 #include "base/callback.h"
  12 #include "base/memory/scoped_ptr.h"
  13
  14 namespace base {
  15 class Value;
  16 }  // namespace base
  17
  18 // Calculates and validates preference value hashes.
  19 class PrefHashCalculator {
  20  public:
  21   enum ValidationResult {
  22     INVALID,
  23     VALID,
  24     // Valid under a deprecated but as secure algorithm.
  25     VALID_SECURE_LEGACY,
  26     // Valid under a deprecated and less secure algorithm.
  27     VALID_WEAK_LEGACY,
  28   };
  29
  30   typedef base::Callback<std::string(const std::string& modern_device_id)>
  31       GetLegacyDeviceIdCallback;
  32
  33   // Constructs a PrefHashCalculator using |seed| and |device_id|. The same
  34   // parameters must be used in order to successfully validate generated hashes.
  35   // |device_id| may be empty.
  36   PrefHashCalculator(const std::string& seed, const std::string& device_id);
  37
  38   // Same as the constructor above, but also specifies that
  39   // |get_legacy_device_id_callback| should be used rather than the default to
  40   // obtain the legacy device id if required.
  41   PrefHashCalculator(
  42       const std::string& seed,
  43       const std::string& device_id,
  44       const GetLegacyDeviceIdCallback& get_legacy_device_id_callback);
  45
  46   ~PrefHashCalculator();
  47
  48   // Calculates a hash value for the supplied preference |path| and |value|.
  49   // |value| may be null if the preference has no value.
  50   std::string Calculate(const std::string& path, const base::Value* value)
  51       const;
  52
  53   // Validates the provided preference hash using current and legacy hashing
  54   // algorithms.
  55   ValidationResult Validate(const std::string& path,
  56                             const base::Value* value,
  57                             const std::string& hash) const;
  58
  59  private:
  60   // Returns the legacy device id based off of |raw_device_id_|. This method
  61   // lazily gets the legacy device id via |get_legacy_device_id_callback_| and
  62   // caches the result in |legacy_device_id_instance_| for future retrievals.
  63   std::string RetrieveLegacyDeviceId() const;
  64
  65   const std::string seed_;
  66   const std::string device_id_;
  67
  68   // The raw device id from which the legacy device id will be derived if
  69   // required.
  70   const std::string raw_device_id_;
  71
  72   const GetLegacyDeviceIdCallback get_legacy_device_id_callback_;
  73
  74   // A cache for the legacy device id which is hard to compute and thus lazily
  75   // computed when/if required (computing the original value for this instance
  76   // is allowed in const methods).
  77   mutable scoped_ptr<const std::string> legacy_device_id_instance_;
  78
  79   DISALLOW_COPY_AND_ASSIGN(PrefHashCalculator);
  80 };
  81
  82 #endif  // CHROME_BROWSER_PREFS_PREF_HASH_CALCULATOR_H_