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      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_
     83