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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_filter_(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) { |
| 25 bloom_filter_.AddString(str); |
| 26 } |
| 27 |
| 28 ByteVector RapporMetric::GetReport(const std::string& secret) const { |
| 29 // Generate a deterministically random mask of fake data using the |
| 30 // client's secret key + real data as a seed. The inclusion of the secret |
| 31 // in the seed avoids correlations between real and fake data. |
| 32 // The seed isn't a human-readable string. |
| 33 std::string personalization_string = metric_name_ + |
| 34 std::string(bytes().begin(), bytes().end()); |
| 35 HmacByteVectorGenerator hmac_generator(bytes().size(), secret, |
| 36 personalization_string); |
| 37 const ByteVector fake_mask = |
| 38 hmac_generator.GetWeightedRandomByteVector(parameters().fake_prob); |
| 39 ByteVector fake_bits = |
| 40 hmac_generator.GetWeightedRandomByteVector(parameters().fake_one_prob); |
| 41 |
| 42 // Redact most of the real data by replacing it with the fake data, hiding |
| 43 // and limiting the amount of information an individual client reports on. |
| 44 const ByteVector* fake_and_redacted_bits = |
| 45 ByteVectorMerge(fake_mask, bytes(), &fake_bits); |
| 46 |
| 47 // Generate biased coin flips for each bit. |
| 48 ByteVectorGenerator coin_generator(bytes().size()); |
| 49 const ByteVector zero_coins = |
| 50 coin_generator.GetWeightedRandomByteVector(parameters().zero_coin_prob); |
| 51 ByteVector one_coins = |
| 52 coin_generator.GetWeightedRandomByteVector(parameters().one_coin_prob); |
| 53 |
| 54 // Create a randomized response report on the fake and redacted data, sending |
| 55 // the outcome of flipping a zero coin for the zero bits in that data, and of |
| 56 // flipping a one coin for the one bits in that data, as the final report. |
| 57 return *ByteVectorMerge(*fake_and_redacted_bits, zero_coins, &one_coins); |
| 58 } |
| 59 |
| 60 } // namespace rappor |
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