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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. The implementation is equivalent to the | |
55 // HMAC_DRBG algorithm from NIST, assuming that all of the bytes can | |
56 // be generated from one request. Therefore, this one instance of this class | |
edknapp
2014/02/11 17:28:00
Something like:
This class only implements a singl
Steven Holte
2014/02/11 22:08:14
Done.
| |
57 // should not be used to generate more than 2^19 bits | |
58 // Ref: http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf | |
59 // We're using our own PRNG instead of crypto::RandBytes because we need to | |
60 // generate a repeatable sequence of bits from the same seed. Conservatively, | |
61 // we're choosing to use HMAC_DRBG here, as it is one of the best studied | |
62 // and standardized ways of generating deterministic, unpredictable sequences | |
63 // based on a secret seed. | |
64 class HmacByteVectorGenerator : public ByteVectorGenerator { | |
65 public: | |
66 // Constructor takes the size of the vector to generate, along with a | |
67 // secret value to seed the pseudo-random number generator. |secret| is | |
68 // treated as an array of bytes. | |
69 HmacByteVectorGenerator(size_t byte_count, const std::string& secret); | |
70 | |
71 ~HmacByteVectorGenerator(); | |
72 | |
73 protected: | |
74 virtual ByteVector GetRandomByteVector() OVERRIDE; | |
75 | |
76 private: | |
77 crypto::HMAC hmac_; | |
78 ByteVector value_; | |
79 size_t requested_bytes_; | |
80 | |
81 DISALLOW_COPY_AND_ASSIGN(HmacByteVectorGenerator); | |
82 }; | |
83 | |
84 } // namespace rappor | |
85 | |
86 #endif // COMPONENTS_RAPPOR_BYTE_VECTOR_UTILS_H_ | |
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