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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 <stddef.h> |
| 9 #include <stdint.h> |
| 10 #include <vector> |
| 11 |
| 12 #include "components/rappor/rappor_parameters.h" |
| 13 #include "crypto/hmac.h" |
| 14 |
| 15 namespace rappor { |
| 16 |
| 17 // A vector of 8-bit integers used to store a set of binary bits. |
| 18 typedef std::vector<uint8_t> ByteVector; |
| 19 |
| 20 // Computes a bitwise OR of byte vectors and stores the result in rhs. |
| 21 ByteVector* ByteVectorOr(const ByteVector& lhs, ByteVector* rhs); |
| 22 |
| 23 // Merges the contents of lhs and rhs vectors according to a mask vector. |
| 24 // Equivalent to (lhs & ~mask) | (rhs & mask). Stores the result in rhs. |
| 25 ByteVector* ByteVectorMerge(const ByteVector& mask, |
| 26 const ByteVector& lhs, |
| 27 ByteVector* rhs); |
| 28 |
| 29 // Counts the number of bits set in the byte vector. |
| 30 int CountBits(const ByteVector& vector); |
| 31 |
| 32 // A utility object for generating random binary data with different |
| 33 // likelihood of bits being true, using entropy from crypto::RandBytes(). |
| 34 class ByteVectorGenerator { |
| 35 public: |
| 36 explicit ByteVectorGenerator(size_t byte_count); |
| 37 |
| 38 ~ByteVectorGenerator(); |
| 39 |
| 40 // Generates a random byte vector where the bits are independent random |
| 41 // variables which are true with the given |probability|. |
| 42 ByteVector GetWeightedRandomByteVector(Probability probability); |
| 43 |
| 44 protected: |
| 45 // Generates a random vector of bytes from a uniform distribution. |
| 46 virtual ByteVector GetRandomByteVector(); |
| 47 |
| 48 size_t byte_count_; |
| 49 |
| 50 DISALLOW_COPY_AND_ASSIGN(ByteVectorGenerator); |
| 51 }; |
| 52 |
| 53 // A ByteVectorGenerator that uses a psuedo-random function to generate a |
| 54 // deterministically random bits. This class only implements a single request |
| 55 // from HMAC_DRBG and streams up to 2^19 bits from that request. |
| 56 // Ref: http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf |
| 57 // We're using our own PRNG instead of crypto::RandBytes because we need to |
| 58 // generate a repeatable sequence of bits from the same seed. Conservatively, |
| 59 // we're choosing to use HMAC_DRBG here, as it is one of the best studied |
| 60 // and standardized ways of generating deterministic, unpredictable sequences |
| 61 // based on a secret seed. |
| 62 class HmacByteVectorGenerator : public ByteVectorGenerator { |
| 63 public: |
| 64 // Constructor takes the size of the vector to generate, along with a |
| 65 // secret value to seed the pseudo-random number generator. |secret| is |
| 66 // treated as an array of bytes. |
| 67 HmacByteVectorGenerator(size_t byte_count, |
| 68 const std::string& entropy_input, |
| 69 const std::string& personalization_string); |
| 70 |
| 71 ~HmacByteVectorGenerator(); |
| 72 |
| 73 static std::string GenerateEntropyInput(); |
| 74 |
| 75 // Key size required for 128-bit security strength (including nonce). |
| 76 static const int kEntropyInputSize = (128 / 8) * 3 / 2; |
| 77 |
| 78 protected: |
| 79 virtual ByteVector GetRandomByteVector() OVERRIDE; |
| 80 |
| 81 private: |
| 82 // HMAC_DRBG_Update |
| 83 void Update(const std::string& provided_data, const ByteVector& key); |
| 84 |
| 85 // HMAC initalized with the value of "Key" HMAC_DRBG_Initialize. |
| 86 crypto::HMAC hmac_; |
| 87 // The "V" value from HMAC_DRBG. |
| 88 ByteVector value_; |
| 89 // Total number of bytes streamed from the HMAC_DRBG Generate Process |
| 90 size_t requested_bytes_; |
| 91 |
| 92 DISALLOW_COPY_AND_ASSIGN(HmacByteVectorGenerator); |
| 93 }; |
| 94 |
| 95 } // namespace rappor |
| 96 |
| 97 #endif // COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ |
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