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// Copyright 2015 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/reports.h"
#include "base/logging.h"
#include "base/rand_util.h"
#include "base/strings/string_piece.h"
#include "components/rappor/byte_vector_utils.h"
#include "components/rappor/public/rappor_parameters.h"
namespace rappor {
namespace internal {
ByteVector GenerateReport(const std::string& secret,
const NoiseParameters& parameters,
const ByteVector& value) {
// Generate a deterministically random mask of fake data using the
// client's secret key + real data as a seed. The inclusion of the secret
// in the seed avoids correlations between real and fake data.
// The seed isn't a human-readable string.
const base::StringPiece personalization_string(
reinterpret_cast<const char*>(&value[0]), value.size());
HmacByteVectorGenerator hmac_generator(value.size(), secret,
personalization_string);
const ByteVector fake_mask =
hmac_generator.GetWeightedRandomByteVector(parameters.fake_prob);
ByteVector fake_bits =
hmac_generator.GetWeightedRandomByteVector(parameters.fake_one_prob);
// Redact most of the real data by replacing it with the fake data, hiding
// and limiting the amount of information an individual client reports on.
const ByteVector* fake_and_redacted_bits =
ByteVectorMerge(fake_mask, value, &fake_bits);
// Generate biased coin flips for each bit.
ByteVectorGenerator coin_generator(value.size());
const ByteVector zero_coins =
coin_generator.GetWeightedRandomByteVector(parameters.zero_coin_prob);
ByteVector one_coins =
coin_generator.GetWeightedRandomByteVector(parameters.one_coin_prob);
// Create a randomized response report on the fake and redacted data, sending
// the outcome of flipping a zero coin for the zero bits in that data, and of
// flipping a one coin for the one bits in that data, as the final report.
return *ByteVectorMerge(*fake_and_redacted_bits, zero_coins, &one_coins);
}
} // namespace internal
} // namespace rappor
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