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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 RapporParameters& parameters, |
| 12 int32_t cohort) |
| 13 : parameters_(parameters), |
| 14 bloom_(parameters.bloom_filter_size_bytes, |
| 15 parameters.bloom_filter_hash_function_count, |
| 16 cohort * parameters.bloom_filter_hash_function_count) { |
| 17 DCHECK_GE(cohort, 0); |
| 18 } |
| 19 |
| 20 RapporMetric::~RapporMetric() {} |
| 21 |
| 22 void RapporMetric::AddSample(const std::string& str) { bloom_.AddString(str); } |
| 23 |
| 24 ByteVector RapporMetric::GetReport(const std::string& secret) const { |
| 25 // Start with the real bloom filter data. |
| 26 const ByteVector real_bits(bytes()); |
| 27 |
| 28 // Generate a deterministically random mask of fake data using the |
| 29 // client's secret key + real data as a seed. |
| 30 std::string seed = secret + parameters()->rappor_name + |
| 31 std::string(real_bits.begin(), real_bits.end()); |
| 32 HmacByteVectorGenerator hmac_generator(real_bits.size(), seed); |
| 33 const ByteVector fake_mask = |
| 34 hmac_generator.GetWeightedRandomByteVector(parameters()->fake_prob); |
| 35 ByteVector fake_ones = |
| 36 hmac_generator.GetWeightedRandomByteVector(parameters()->fake_one_prob); |
| 37 |
| 38 // Redact most of the real data by replacing it with the fake data, hiding |
| 39 // and limiting the amount of information an individual client reports on. |
| 40 const ByteVector* redacted_bits = |
| 41 ByteVectorMerge(fake_mask, real_bits, &fake_ones); |
| 42 |
| 43 // Generate biased coin flips for each bit. |
| 44 ByteVectorGenerator coin_generator(real_bits.size()); |
| 45 const ByteVector zero_coins = |
| 46 coin_generator.GetWeightedRandomByteVector(parameters()->zero_coin_prob); |
| 47 ByteVector one_coins = |
| 48 coin_generator.GetWeightedRandomByteVector(parameters()->one_coin_prob); |
| 49 |
| 50 // Use the redacted data to select which coin type is used for each bit in |
| 51 // the final report. |
| 52 const ByteVector* output = |
| 53 ByteVectorMerge(*redacted_bits, zero_coins, &one_coins); |
| 54 |
| 55 return *output; |
| 56 } |
| 57 |
| 58 } // namespace rappor |
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