1 // mersenne.h - written and placed in public domain by Jeffrey Walton.
2
3 /// \file mersenne.h
4 /// \brief Class file for Mersenne Twister
5 /// \warning MersenneTwister is suitable for Monte-Carlo simulations, where uniformaly distrubuted
6 /// numbers are required quickly. It should not be used for cryptographic purposes.
7 /// \since Crypto++ 5.6.3
8 #ifndef CRYPTOPP_MERSENNE_TWISTER_H
9 #define CRYPTOPP_MERSENNE_TWISTER_H
10
11 #include "cryptlib.h"
12 #include "secblock.h"
13 #include "misc.h"
14
NAMESPACE_BEGIN(CryptoPP)15 NAMESPACE_BEGIN(CryptoPP)
16
17 /// \brief Mersenne Twister class for Monte-Carlo simulations
18 /// \tparam K Magic constant
19 /// \tparam M Period parameter
20 /// \tparam N Size of the state vector
21 /// \tparam F Multiplier constant
22 /// \tparam S Initial seed
23 /// \details Provides the MersenneTwister implementation. The class is a header-only implementation.
24 /// \details You should reseed the generator after a fork() to avoid multiple generators
25 /// with the same internal state.
26 /// \warning MersenneTwister is suitable for simulations, where uniformaly distrubuted numbers are
27 /// required quickly. It should not be used for cryptographic purposes.
28 /// \sa MT19937, MT19937ar
29 /// \since Crypto++ 5.6.3
30 template <unsigned int K, unsigned int M, unsigned int N, unsigned int F, word32 S>
31 class MersenneTwister : public RandomNumberGenerator
32 {
33 public:
34 CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() { return (S==5489 ? "MT19937ar" : (S==4537 ? "MT19937" : "MT19937x")); }
35
36 ~MersenneTwister() {}
37
38 /// \brief Construct a Mersenne Twister
39 /// \param seed 32-bit seed
40 /// \details Defaults to template parameter S due to changing algorithm
41 /// parameters over time
42 MersenneTwister(word32 seed = S) : m_idx(N)
43 {
44 Reset(seed);
45 }
46
47 bool CanIncorporateEntropy() const {return true;}
48
49 /// \brief Update RNG state with additional unpredictable values
50 /// \param input the entropy to add to the generator
51 /// \param length the size of the input buffer
52 /// \details MersenneTwister uses the first 32-bits of <tt>input</tt> to reseed the
53 /// generator. If fewer bytes are provided, then the seed is padded with 0's.
54 void IncorporateEntropy(const byte *input, size_t length)
55 {
56 // Handle word32 size blocks
57 FixedSizeSecBlock<word32, 1> temp;
58 temp[0] = 0;
59
60 if (length > 4)
61 length = 4;
62
63 for (size_t i=0; i<length; ++i)
64 {
65 temp[0] <<= 8;
66 temp[0] = temp[0] | input[i];
67 }
68
69 Reset(temp[0]);
70 }
71
72 /// \brief Generate random array of bytes
73 /// \param output byte buffer
74 /// \param size length of the buffer, in bytes
75 /// \details Bytes are written to output in big endian order. If output length
76 /// is not a multiple of word32, then unused bytes are not accumulated for subsequent
77 /// calls to GenerateBlock. Rather, the unused tail bytes are discarded, and the
78 /// stream is continued at the next word32 boundary from the state array.
79 void GenerateBlock(byte *output, size_t size)
80 {
81 // Handle word32 size blocks
82 FixedSizeSecBlock<word32, 1> temp;
83 for (size_t i=0; i < size/4; i++, output += 4)
84 {
85 temp[0] = NextMersenneWord();
86 memcpy(output, temp+0, 4);
87 }
88
89 // No tail bytes
90 if (size%4 == 0)
91 return;
92
93 // Handle tail bytes
94 temp[0] = NextMersenneWord();
95 switch (size%4)
96 {
97 case 3: output[2] = CRYPTOPP_GET_BYTE_AS_BYTE(temp[0], 1); /* fall through */
98 case 2: output[1] = CRYPTOPP_GET_BYTE_AS_BYTE(temp[0], 2); /* fall through */
99 case 1: output[0] = CRYPTOPP_GET_BYTE_AS_BYTE(temp[0], 3); break;
100
101 default: CRYPTOPP_ASSERT(0);;
102 }
103 }
104
105 /// \brief Generate a random 32-bit word in the range min to max, inclusive
106 /// \return random 32-bit word in the range min to max, inclusive
107 /// \details If the 32-bit candidate is not within the range, then it is discarded
108 /// and a new candidate is used.
109 word32 GenerateWord32(word32 min=0, word32 max=0xffffffffL)
110 {
111 const word32 range = max-min;
112 if (range == 0xffffffffL)
113 return NextMersenneWord();
114
115 const int maxBits = BitPrecision(range);
116 word32 value;
117
118 do{
119 value = Crop(NextMersenneWord(), maxBits);
120 } while (value > range);
121
122 return value+min;
123 }
124
125 /// \brief Generate and discard n bytes
126 /// \param n the number of bytes to discard, rounded up to a <tt>word32</tt> size
127 /// \details If n is not a multiple of <tt>word32</tt>, then unused bytes are
128 /// not accumulated for subsequent calls to GenerateBlock. Rather, the unused
129 /// tail bytes are discarded, and the stream is continued at the next
130 /// <tt>word32</tt> boundary from the state array.
131 void DiscardBytes(size_t n)
132 {
133 for(size_t i=0; i < RoundUpToMultipleOf(n, 4U); i++)
134 NextMersenneWord();
135 }
136
137 protected:
138
139 void Reset(word32 seed)
140 {
141 m_idx = N;
142
143 m_state[0] = seed;
144 for (unsigned int i = 1; i < N+1; i++)
145 m_state[i] = word32(F * (m_state[i-1] ^ (m_state[i-1] >> 30)) + i);
146 }
147
148 /// \brief Returns the next 32-bit word from the state array
149 /// \return the next 32-bit word from the state array
150 /// \details fetches the next word frm the state array, performs bit operations on
151 /// it, and then returns the value to the caller.
152 word32 NextMersenneWord()
153 {
154 if (m_idx >= N) { Twist(); }
155
156 word32 temp = m_state[m_idx++];
157
158 temp ^= (temp >> 11);
159 temp ^= (temp << 7) & 0x9D2C5680; // 0x9D2C5680 (2636928640)
160 temp ^= (temp << 15) & 0xEFC60000; // 0xEFC60000 (4022730752)
161
162 return temp ^ (temp >> 18);
163 }
164
165 /// \brief Performs the twist operaton on the state array
166 void Twist()
167 {
168 static const word32 magic[2]={0x0UL, K};
169 word32 kk, temp;
170
171 CRYPTOPP_ASSERT(N >= M);
172 for (kk=0;kk<N-M;kk++)
173 {
174 temp = (m_state[kk] & 0x80000000)|(m_state[kk+1] & 0x7FFFFFFF);
175 m_state[kk] = m_state[kk+M] ^ (temp >> 1) ^ magic[temp & 0x1UL];
176 }
177
178 for (;kk<N-1;kk++)
179 {
180 temp = (m_state[kk] & 0x80000000)|(m_state[kk+1] & 0x7FFFFFFF);
181 m_state[kk] = m_state[kk+(M-N)] ^ (temp >> 1) ^ magic[temp & 0x1UL];
182 }
183
184 temp = (m_state[N-1] & 0x80000000)|(m_state[0] & 0x7FFFFFFF);
185 m_state[N-1] = m_state[M-1] ^ (temp >> 1) ^ magic[temp & 0x1UL];
186
187 // Reset index
188 m_idx = 0;
189
190 // Wipe temp
191 SecureWipeArray(&temp, 1);
192 }
193
194 private:
195
196 /// \brief 32-bit word state array of size N
197 FixedSizeSecBlock<word32, N+1> m_state;
198 /// \brief the current index into the state array
199 word32 m_idx;
200 };
201
202 /// \brief Original MT19937 generator provided in the ACM paper.
203 /// \details MT19937 uses 4537 as default initial seed.
204 /// \details You should reseed the generator after a fork() to avoid multiple generators
205 /// with the same internal state.
206 /// \sa MT19937ar, <A HREF="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/ARTICLES/mt.pdf">Mersenne twister:
207 /// a 623-dimensionally equidistributed uniform pseudo-random number generator</A>
208 /// \since Crypto++ 5.6.3
209 #if CRYPTOPP_DOXYGEN_PROCESSING
210 class MT19937 : public MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x10DCD /*69069*/, 4537> {};
211 #else
212 typedef MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x10DCD /*69069*/, 4537> MT19937;
213 #endif
214
215 /// \brief Updated MT19937 generator adapted to provide an array for initialization.
216 /// \details MT19937 uses 5489 as default initial seed. Use this generator when interoperating with C++11's
217 /// mt19937 class.
218 /// \details You should reseed the generator after a fork() to avoid multiple generators
219 /// with the same internal state.
220 /// \sa MT19937, <A HREF="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html">Mersenne Twister
221 /// with improved initialization</A>
222 /// \since Crypto++ 5.6.3
223 #if CRYPTOPP_DOXYGEN_PROCESSING
224 class MT19937ar : public MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x6C078965 /*1812433253*/, 5489> {};
225 #else
226 typedef MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x6C078965 /*1812433253*/, 5489> MT19937ar;
227 #endif
228
229 NAMESPACE_END
230
231 #endif // CRYPTOPP_MERSENNE_TWISTER_H
232