RAPPOR implementation

components/rappor/byte_vector_utils.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_
+#define COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include <vector>
+
+#include "components/rappor/rappor_parameters.h"
+#include "crypto/hmac.h"
+
+namespace rappor {
+
+// A vector of one byte integers used to store a set of binary bits.
+typedef std::vector<uint8_t> ByteVector;
+
+// Computes a bitwise OR of byte vectors and stores the result in rhs.
+ByteVector* ByteVectorOr(const ByteVector& lhs, ByteVector* rhs);
+
+// Merges the contents of lhs and rhs  vectors according to a mask vector.
+// Equivalent to (lhs & ~mask) | (rhs & mask).  Stores the result in rhs.
+ByteVector* ByteVectorMerge(const ByteVector& mask,
+                            const ByteVector& lhs,
+                            ByteVector* rhs);
+
+// A utility object for generating random binary data with different
+// likelihood of bits being true.
+class ByteVectorGenerator {
+ public:
+  explicit ByteVectorGenerator(size_t byte_count);
+
+  ~ByteVectorGenerator();
+
+  // Generates a random byte vector where each bit is independently set with
+  // the given probability.
+  ByteVector GetWeightedRandomByteVector(Probability probability);
+
+ protected:
+  // Generates a random byte from a uniform distribution.
+  virtual uint8_t RandByte();
+
+ private:
+  // Generates a random vector of bytes from a uniform distribution.
+  ByteVector GetRandomByteVector();
+
+  size_t byte_count_;
+
+  DISALLOW_COPY_AND_ASSIGN(ByteVectorGenerator);
+};
+
+// A ByteVectorGenerator that uses a psuedo-random function to generate
+// deterministicly random bits.
+class HmacByteVectorGenerator : public ByteVectorGenerator {
+ public:
+  // Constructor takes the size of the vector to generate, along with a
+  // secret value to seed the pseudo-random number generator.
+  HmacByteVectorGenerator(size_t byte_count, const std::string& secret);
+
+  ~HmacByteVectorGenerator();
+
+ protected:
+  virtual uint8_t RandByte() OVERRIDE;
+
+ private:
+  crypto::HMAC hmac_;
+  uint64_t hmac_state_;
+
+  DISALLOW_COPY_AND_ASSIGN(HmacByteVectorGenerator);
+};
+
+}  // namespace rappor
+
+#endif  // COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_