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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 #include #include #include "base/macros.h" #include "base/strings/string_piece.h" #include "components/rappor/public/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 ByteVector; // Converts the lowest |size| bytes of |value| into a ByteVector. void Uint64ToByteVector(uint64_t value, size_t size, ByteVector* output); // Computes a bitwise AND of byte vectors and stores the result in rhs. // Returns rhs for chaining. ByteVector* ByteVectorAnd(const ByteVector& lhs, ByteVector* rhs); // 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); virtual ~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 pseudo-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, base::StringPiece personalization_string); ~HmacByteVectorGenerator() override; // 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: 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_