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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 #ifndef COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |
| 6 #define COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |
| 7 |
| 8 #include <vector> |
| 9 |
| 10 #include "base/basictypes.h" |
| 11 #include "components/rappor/rappor_parameters.h" |
| 12 #include "crypto/hmac.h" |
| 13 |
| 14 namespace rappor { |
| 15 |
| 16 // A vector of 8-bit integers used to store a set of binary bits. |
| 17 typedef std::vector<uint8_t> ByteVector; |
| 18 |
| 19 // Computes a bitwise OR of byte vectors and stores the result in rhs. |
| 20 // Returns rhs for chaining. |
| 21 ByteVector* ByteVectorOr(const ByteVector& lhs, ByteVector* rhs); |
| 22 |
| 23 // Merges the contents of lhs and rhs vectors according to a mask vector. |
| 24 // The i-th bit of the result vector will be the i-th bit of either the lhs |
| 25 // or rhs vector, based on the i-th bit of the mask vector. |
| 26 // Equivalent to (lhs & ~mask) | (rhs & mask). Stores the result in rhs. |
| 27 // Returns rhs for chaining. |
| 28 ByteVector* ByteVectorMerge(const ByteVector& mask, |
| 29 const ByteVector& lhs, |
| 30 ByteVector* rhs); |
| 31 |
| 32 // Counts the number of bits set in the byte vector. |
| 33 int CountBits(const ByteVector& vector); |
| 34 |
| 35 // A utility object for generating random binary data with different |
| 36 // likelihood of bits being true, using entropy from crypto::RandBytes(). |
| 37 class ByteVectorGenerator { |
| 38 public: |
| 39 explicit ByteVectorGenerator(size_t byte_count); |
| 40 |
| 41 ~ByteVectorGenerator(); |
| 42 |
| 43 // Generates a random byte vector where the bits are independent random |
| 44 // variables which are true with the given |probability|. |
| 45 ByteVector GetWeightedRandomByteVector(Probability probability); |
| 46 |
| 47 protected: |
| 48 // Size of vectors to be generated. |
| 49 size_t byte_count() const { return byte_count_; } |
| 50 |
| 51 // Generates a random vector of bytes from a uniform distribution. |
| 52 virtual ByteVector GetRandomByteVector(); |
| 53 |
| 54 private: |
| 55 size_t byte_count_; |
| 56 |
| 57 DISALLOW_COPY_AND_ASSIGN(ByteVectorGenerator); |
| 58 }; |
| 59 |
| 60 // A ByteVectorGenerator that uses a psuedo-random function to generate a |
| 61 // deterministically random bits. This class only implements a single request |
| 62 // from HMAC_DRBG and streams up to 2^19 bits from that request. |
| 63 // Ref: http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf |
| 64 // We're using our own PRNG instead of crypto::RandBytes because we need to |
| 65 // generate a repeatable sequence of bits from the same seed. Conservatively, |
| 66 // we're choosing to use HMAC_DRBG here, as it is one of the best studied |
| 67 // and standardized ways of generating deterministic, unpredictable sequences |
| 68 // based on a secret seed. |
| 69 class HmacByteVectorGenerator : public ByteVectorGenerator { |
| 70 public: |
| 71 // Constructor takes the size of the vector to generate, along with a |
| 72 // |entropy_input| and |personalization_string| to seed the pseudo-random |
| 73 // number generator. The string parameters are treated as byte arrays. |
| 74 HmacByteVectorGenerator(size_t byte_count, |
| 75 const std::string& entropy_input, |
| 76 const std::string& personalization_string); |
| 77 |
| 78 ~HmacByteVectorGenerator(); |
| 79 |
| 80 // Generates a random string suitable for passing to the constructor as |
| 81 // |entropy_input|. |
| 82 static std::string GenerateEntropyInput(); |
| 83 |
| 84 // Key size required for 128-bit security strength (including nonce). |
| 85 static const size_t kEntropyInputSize; |
| 86 |
| 87 protected: |
| 88 // Generate byte vector generator that streams from the next request instead |
| 89 // of the current one. For testing against NIST test vectors only. |
| 90 explicit HmacByteVectorGenerator(const HmacByteVectorGenerator& prev_request); |
| 91 |
| 92 // ByteVector implementation: |
| 93 virtual ByteVector GetRandomByteVector() OVERRIDE; |
| 94 |
| 95 private: |
| 96 // HMAC initalized with the value of "Key" HMAC_DRBG_Initialize. |
| 97 crypto::HMAC hmac_; |
| 98 |
| 99 // The "V" value from HMAC_DRBG. |
| 100 ByteVector value_; |
| 101 |
| 102 // Total number of bytes streamed from the HMAC_DRBG Generate Process. |
| 103 size_t generated_bytes_; |
| 104 |
| 105 DISALLOW_ASSIGN(HmacByteVectorGenerator); |
| 106 }; |
| 107 |
| 108 } // namespace rappor |
| 109 |
| 110 #endif // COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |
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