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| 1 // Copyright 2014 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 #include "components/rappor/rappor_metric.h" |
| 6 |
| 7 #include "base/logging.h" |
| 8 |
| 9 namespace rappor { |
| 10 |
| 11 RapporMetric::RapporMetric(const std::string& metric_name, |
| 12 const RapporParameters& parameters, |
| 13 int32_t cohort) |
| 14 : metric_name_(metric_name), |
| 15 parameters_(parameters), |
| 16 bloom_(parameters.bloom_filter_size_bytes, |
| 17 parameters.bloom_filter_hash_function_count, |
| 18 cohort * parameters.bloom_filter_hash_function_count) { |
| 19 DCHECK_GE(cohort, 0); |
| 20 } |
| 21 |
| 22 RapporMetric::~RapporMetric() {} |
| 23 |
| 24 void RapporMetric::AddSample(const std::string& str) { bloom_.AddString(str); } |
| 25 |
| 26 ByteVector RapporMetric::GetReport(const std::string& secret) const { |
| 27 // Generate a deterministically random mask of fake data using the |
| 28 // client's secret key + real data as a seed. The inclusion of the secret |
| 29 // in the seed avoids correlations between real and fake data. |
| 30 // The seed isn't a human-readable string. |
| 31 std::string seed = secret + metric_name_ + |
| 32 std::string(bytes().begin(), bytes().end()); |
| 33 HmacByteVectorGenerator hmac_generator(bytes().size(), seed); |
| 34 const ByteVector fake_mask = |
| 35 hmac_generator.GetWeightedRandomByteVector(parameters().fake_prob); |
| 36 ByteVector fake_ones = |
| 37 hmac_generator.GetWeightedRandomByteVector(parameters().fake_one_prob); |
| 38 |
| 39 // Redact most of the real data by replacing it with the fake data, hiding |
| 40 // and limiting the amount of information an individual client reports on. |
| 41 const ByteVector* fake_and_redacted_bits = |
| 42 ByteVectorMerge(fake_mask, bytes(), &fake_ones); |
| 43 |
| 44 // Generate biased coin flips for each bit. |
| 45 ByteVectorGenerator coin_generator(bytes().size()); |
| 46 const ByteVector zero_coins = |
| 47 coin_generator.GetWeightedRandomByteVector(parameters().zero_coin_prob); |
| 48 ByteVector one_coins = |
| 49 coin_generator.GetWeightedRandomByteVector(parameters().one_coin_prob); |
| 50 |
| 51 // Create a randomized response report on the fake and redacted data, sending |
| 52 // the outcome of flipping a zero coin for the zero bits in that data, and of |
| 53 // flipping a one coin for the one bits in that data, as the final report. |
| 54 return *ByteVectorMerge(*fake_and_redacted_bits, zero_coins, &one_coins); |
| 55 } |
| 56 |
| 57 } // namespace rappor |
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