| // 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. |
| |
| #include "components/rappor/rappor_metric.h" |
| |
| #include "base/logging.h" |
| |
| namespace rappor { |
| |
| RapporMetric::RapporMetric(const std::string& metric_name, |
| const RapporParameters& parameters, |
| int32_t cohort) |
| : metric_name_(metric_name), |
| parameters_(parameters), |
| bloom_filter_(parameters.bloom_filter_size_bytes, |
| parameters.bloom_filter_hash_function_count, |
| cohort * parameters.bloom_filter_hash_function_count) { |
| DCHECK_GE(cohort, 0); |
| } |
| |
| RapporMetric::~RapporMetric() {} |
| |
| void RapporMetric::AddSample(const std::string& str) { |
| bloom_filter_.AddString(str); |
| } |
| |
| ByteVector RapporMetric::GetReport(const std::string& secret) const { |
| // 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 std::string personalization_string = metric_name_ + |
| std::string(bytes().begin(), bytes().end()); |
| HmacByteVectorGenerator hmac_generator(bytes().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, bytes(), &fake_bits); |
| |
| // Generate biased coin flips for each bit. |
| ByteVectorGenerator coin_generator(bytes().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 rappor |