Index: components/rappor/byte_vector_utils.h |
diff --git a/components/rappor/byte_vector_utils.h b/components/rappor/byte_vector_utils.h |
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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. |
+ |
+#ifndef COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |
+#define COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |
+ |
+#include <vector> |
+ |
+#include "base/basictypes.h" |
+#include "components/rappor/rappor_parameters.h" |
+#include "crypto/hmac.h" |
+ |
+namespace rappor { |
+ |
+// A vector of 8-bit integers used to store a set of binary bits. |
+typedef std::vector<uint8_t> ByteVector; |
+ |
+// Computes a bitwise OR of byte vectors and stores the result in rhs. |
+// Returns rhs for chaining. |
+ByteVector* ByteVectorOr(const ByteVector& lhs, ByteVector* rhs); |
+ |
+// Merges the contents of lhs and rhs vectors according to a mask vector. |
+// The i-th bit of the result vector will be the i-th bit of either the lhs |
+// or rhs vector, based on the i-th bit of the mask vector. |
+// Equivalent to (lhs & ~mask) | (rhs & mask). Stores the result in rhs. |
+// Returns rhs for chaining. |
+ByteVector* ByteVectorMerge(const ByteVector& mask, |
+ const ByteVector& lhs, |
+ ByteVector* rhs); |
+ |
+// Counts the number of bits set in the byte vector. |
+int CountBits(const ByteVector& vector); |
+ |
+// A utility object for generating random binary data with different |
+// likelihood of bits being true, using entropy from crypto::RandBytes(). |
+class ByteVectorGenerator { |
+ public: |
+ explicit ByteVectorGenerator(size_t byte_count); |
+ |
+ ~ByteVectorGenerator(); |
+ |
+ // Generates a random byte vector where the bits are independent random |
+ // variables which are true with the given |probability|. |
+ ByteVector GetWeightedRandomByteVector(Probability probability); |
+ |
+ protected: |
+ // Size of vectors to be generated. |
+ size_t byte_count() const { return byte_count_; } |
+ |
+ // Generates a random vector of bytes from a uniform distribution. |
+ virtual ByteVector GetRandomByteVector(); |
+ |
+ private: |
+ size_t byte_count_; |
+ |
+ DISALLOW_COPY_AND_ASSIGN(ByteVectorGenerator); |
+}; |
+ |
+// A ByteVectorGenerator that uses a psuedo-random function to generate a |
+// deterministically random bits. This class only implements a single request |
+// from HMAC_DRBG and streams up to 2^19 bits from that request. |
+// Ref: http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf |
+// We're using our own PRNG instead of crypto::RandBytes because we need to |
+// generate a repeatable sequence of bits from the same seed. Conservatively, |
+// we're choosing to use HMAC_DRBG here, as it is one of the best studied |
+// and standardized ways of generating deterministic, unpredictable sequences |
+// based on a secret seed. |
+class HmacByteVectorGenerator : public ByteVectorGenerator { |
+ public: |
+ // Constructor takes the size of the vector to generate, along with a |
+ // |entropy_input| and |personalization_string| to seed the pseudo-random |
+ // number generator. The string parameters are treated as byte arrays. |
+ HmacByteVectorGenerator(size_t byte_count, |
+ const std::string& entropy_input, |
+ const std::string& personalization_string); |
+ |
+ ~HmacByteVectorGenerator(); |
+ |
+ // Generates a random string suitable for passing to the constructor as |
+ // |entropy_input|. |
+ static std::string GenerateEntropyInput(); |
+ |
+ // Key size required for 128-bit security strength (including nonce). |
+ static const size_t kEntropyInputSize; |
+ |
+ protected: |
+ // Generate byte vector generator that streams from the next request instead |
+ // of the current one. For testing against NIST test vectors only. |
+ explicit HmacByteVectorGenerator(const HmacByteVectorGenerator& prev_request); |
+ |
+ // ByteVector implementation: |
+ virtual ByteVector GetRandomByteVector() OVERRIDE; |
+ |
+ private: |
+ // HMAC initalized with the value of "Key" HMAC_DRBG_Initialize. |
+ crypto::HMAC hmac_; |
+ |
+ // The "V" value from HMAC_DRBG. |
+ ByteVector value_; |
+ |
+ // Total number of bytes streamed from the HMAC_DRBG Generate Process. |
+ size_t generated_bytes_; |
+ |
+ DISALLOW_ASSIGN(HmacByteVectorGenerator); |
+}; |
+ |
+} // namespace rappor |
+ |
+#endif // COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |