RAPPOR implementation

components/rappor/byte_vector_utils.cc

+// Copyright (c) 2013 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.
+
+#include "components/rappor/byte_vector_utils.h"
+
+#include <string>
+
+#include "base/logging.h"
+#include "base/strings/string_number_conversions.h"
+#include "crypto/hmac.h"
+#include "crypto/random.h"
+
+namespace rappor {
+
+ByteVector* ByteVectorAnd(ByteVector* lhs, const ByteVector& rhs) {
+  DCHECK_EQ(lhs->size(), rhs.size());
+  for (size_t i = 0, len = rhs.size(); i < len; i++) {
+    (*lhs)[i] = (*lhs)[i] & rhs[i];
+  }
+  return lhs;
+}
+
+ByteVector* ByteVectorOr(ByteVector* lhs, const ByteVector& rhs) {
+  DCHECK_EQ(lhs->size(), rhs.size());
+  for (size_t i = 0, len = rhs.size(); i < len; i++) {
+    (*lhs)[i] = (*lhs)[i] | rhs[i];
+  }
+  return lhs;
+}
+
+ByteVector* ByteVectorMerge(ByteVector* lhs,
+                            const ByteVector& rhs,
+                            const ByteVector& mask) {
+  DCHECK_EQ(lhs->size(), rhs.size());
+  for (size_t i = 0, len = rhs.size(); i < len; i++) {
+    (*lhs)[i] = ((*lhs)[i] & ~mask[i]) | (rhs[i] & mask[i]);
+  }
+  return lhs;
+}
+
+ByteVectorGenerator::ByteVectorGenerator(size_t byte_count)
+    : byte_count_(byte_count) {}
+
+uint8_t ByteVectorGenerator::RandByte() {
+  uint8_t random_bits;
+  crypto::RandBytes(&random_bits, sizeof(uint8_t));
+  return random_bits;
+}
+
+ByteVector ByteVectorGenerator::GetRandomByteVector() {
+  ByteVector bytes(byte_count_);
+  for (size_t i = 0; i < byte_count_; i++) {
+    bytes[i] = RandByte();
+  }
+  return bytes;
+}
+
+ByteVector ByteVectorGenerator::GetWeightedRandomByteVector(
+    Probability probability) {
+  ByteVector bytes = GetRandomByteVector();
+  switch (probability) {
+    case PROBABILITY_87_5:
+      return *ByteVectorOr(ByteVectorOr(&bytes, GetRandomByteVector()),
+                           GetRandomByteVector());
+    case PROBABILITY_75:
+      return *ByteVectorOr(&bytes, GetRandomByteVector());
+    case PROBABILITY_50:
+      return bytes;
+    case PROBABILITY_25:
+      return *ByteVectorAnd(&bytes, GetRandomByteVector());
+    case PROBABILITY_12_5:
+      return *ByteVectorAnd(ByteVectorAnd(&bytes, GetRandomByteVector()),
+                            GetRandomByteVector());
+    default:
+      // Invalid probability for coin flips
+      abort();
+  }
+}
+
+HmacByteVectorGenerator::HmacByteVectorGenerator(size_t byte_count,
+                                                 const std::string& secret)
+    : ByteVectorGenerator(byte_count), hmac_(crypto::HMAC::SHA256) {
+  // A completely arbitrary value for the initial value of an
+  // HmacByteVectorGenerator's state. The initial digits of pi.
+  const uint64_t kHmacInitialState = 3141592653589793;
+
+  if (!hmac_.Init(secret)) {
+    abort();
+  };
+  assert(hmac_.DigestLength() > sizeof(uint64_t));
+  hmac_state_ = kHmacInitialState;
+}
+
+uint8_t HmacByteVectorGenerator::RandByte() {
+  uint8_t random_bits;
+  std::string state = base::Uint64ToString(hmac_state_);
+  if (!hmac_.Sign(state, &random_bits, sizeof(uint8_t))) {
+    abort();
+  }
+  ++hmac_state_;
+  return random_bits;
+}
+
+}  // namespace rappor