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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 namespace rappor { |
| 8 |
| 9 RapporMetric::RapporMetric(const RapporParameters& parameters) |
| 10 : parameters_(parameters), |
| 11 bloom_(parameters.bloom_filter_size_bytes, |
| 12 parameters.bloom_filter_hash_function_count) {} |
| 13 |
| 14 RapporMetric::~RapporMetric() {} |
| 15 |
| 16 void RapporMetric::AddSamples(const std::vector<std::string>& strings) { |
| 17 bloom_.AddStrings(strings); |
| 18 } |
| 19 |
| 20 void RapporMetric::AddSample(const std::string& str) { bloom_.AddString(str); } |
| 21 |
| 22 ByteVector RapporMetric::GetReport(const std::string& secret) const { |
| 23 // Start with the real bloom filter data. |
| 24 const ByteVector real_bits(bytes()); |
| 25 |
| 26 // Generate a deterministically random mask of fake data based on the |
| 27 // client's secret key. |
| 28 HmacByteVectorGenerator hmac_generator(real_bits.size(), |
| 29 secret + parameters()->rappor_name); |
| 30 const ByteVector fake_mask = |
| 31 hmac_generator.GetWeightedRandomByteVector(parameters()->fake_prob); |
| 32 ByteVector fake_ones = |
| 33 hmac_generator.GetWeightedRandomByteVector(parameters()->fake_one_prob); |
| 34 |
| 35 // Redact most of the real data by replacing it with the fake data, hiding |
| 36 // and limiting the amount of information an individual client reports on. |
| 37 const ByteVector* redacted_bits = |
| 38 ByteVectorMerge(fake_mask, real_bits, &fake_ones); |
| 39 |
| 40 // Generate biased coin flips for each bit. |
| 41 ByteVectorGenerator coin_generator(real_bits.size()); |
| 42 const ByteVector zero_coins = |
| 43 coin_generator.GetWeightedRandomByteVector(parameters()->zero_coin_prob); |
| 44 ByteVector one_coins = |
| 45 coin_generator.GetWeightedRandomByteVector(parameters()->one_coin_prob); |
| 46 |
| 47 // Use the redacted data to select which coin type is used for each bit in |
| 48 // the final report. |
| 49 const ByteVector* output = |
| 50 ByteVectorMerge(*redacted_bits, zero_coins, &one_coins); |
| 51 |
| 52 return *output; |
| 53 } |
| 54 |
| 55 } // namespace rappor |
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