Index: components/rappor/rappor_metric.cc |
diff --git a/components/rappor/rappor_metric.cc b/components/rappor/rappor_metric.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..2da3b312b77dbe72ebd416b6f3b24635d2126a64 |
--- /dev/null |
+++ b/components/rappor/rappor_metric.cc |
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+// 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. |
+ 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 |