mersenne.h
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// mersenne.h - written and placed in public domain by Jeffrey Walton.
/// \file mersenne.h
/// \brief Class file for Mersenne Twister
/// \warning MersenneTwister is suitable for Monte-Carlo simulations, where uniformaly distrubuted
/// numbers are required quickly. It should not be used for cryptographic purposes.
/// \since Crypto++ 5.6.3
#ifndef CRYPTOPP_MERSENNE_TWISTER_H
#define CRYPTOPP_MERSENNE_TWISTER_H
#include "cryptlib.h"
#include "secblock.h"
#include "misc.h"
NAMESPACE_BEGIN(CryptoPP)
/// \brief Mersenne Twister class for Monte-Carlo simulations
/// \tparam K Magic constant
/// \tparam M Period parameter
/// \tparam N Size of the state vector
/// \tparam F Multiplier constant
/// \tparam S Initial seed
/// \details Provides the MersenneTwister implementation. The class is a header-only implementation.
/// \details You should reseed the generator after a fork() to avoid multiple generators
/// with the same internal state.
/// \warning MersenneTwister is suitable for simulations, where uniformaly distrubuted numbers are
/// required quickly. It should not be used for cryptographic purposes.
/// \sa MT19937, MT19937ar
/// \since Crypto++ 5.6.3
template <unsigned int K, unsigned int M, unsigned int N, unsigned int F, word32 S>
class MersenneTwister : public RandomNumberGenerator
{
public:
CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() { return (S==5489 ? "MT19937ar" : (S==4537 ? "MT19937" : "MT19937x")); }
~MersenneTwister() {}
/// \brief Construct a Mersenne Twister
/// \param seed 32-bit seed
/// \details Defaults to template parameter S due to changing algorithm
/// parameters over time
MersenneTwister(word32 seed = S) : m_idx(N)
{
Reset(seed);
}
bool CanIncorporateEntropy() const {return true;}
/// \brief Update RNG state with additional unpredictable values
/// \param input the entropy to add to the generator
/// \param length the size of the input buffer
/// \details MersenneTwister uses the first 32-bits of <tt>input</tt> to reseed the
/// generator. If fewer bytes are provided, then the seed is padded with 0's.
void IncorporateEntropy(const byte *input, size_t length)
{
// Handle word32 size blocks
FixedSizeSecBlock<word32, 1> temp;
temp[0] = 0;
if (length > 4)
length = 4;
for (size_t i=0; i<length; ++i)
{
temp[0] <<= 8;
temp[0] = temp[0] | input[i];
}
Reset(temp[0]);
}
/// \brief Generate random array of bytes
/// \param output byte buffer
/// \param size length of the buffer, in bytes
/// \details Bytes are written to output in big endian order. If output length
/// is not a multiple of word32, then unused bytes are not accumulated for subsequent
/// calls to GenerateBlock. Rather, the unused tail bytes are discarded, and the
/// stream is continued at the next word32 boundary from the state array.
void GenerateBlock(byte *output, size_t size)
{
// Handle word32 size blocks
FixedSizeSecBlock<word32, 1> temp;
for (size_t i=0; i < size/4; i++, output += 4)
{
temp[0] = NextMersenneWord();
memcpy(output, temp+0, 4);
}
// No tail bytes
if (size%4 == 0)
return;
// Handle tail bytes
temp[0] = NextMersenneWord();
switch (size%4)
{
case 3: output[2] = CRYPTOPP_GET_BYTE_AS_BYTE(temp[0], 1); /* fall through */
case 2: output[1] = CRYPTOPP_GET_BYTE_AS_BYTE(temp[0], 2); /* fall through */
case 1: output[0] = CRYPTOPP_GET_BYTE_AS_BYTE(temp[0], 3); break;
default: CRYPTOPP_ASSERT(0);;
}
}
/// \brief Generate a random 32-bit word in the range min to max, inclusive
/// \return random 32-bit word in the range min to max, inclusive
/// \details If the 32-bit candidate is not within the range, then it is discarded
/// and a new candidate is used.
word32 GenerateWord32(word32 min=0, word32 max=0xffffffffL)
{
const word32 range = max-min;
if (range == 0xffffffffL)
return NextMersenneWord();
const int maxBits = BitPrecision(range);
word32 value;
do{
value = Crop(NextMersenneWord(), maxBits);
} while (value > range);
return value+min;
}
/// \brief Generate and discard n bytes
/// \param n the number of bytes to discard, rounded up to a <tt>word32</tt> size
/// \details If n is not a multiple of <tt>word32</tt>, then unused bytes are
/// not accumulated for subsequent calls to GenerateBlock. Rather, the unused
/// tail bytes are discarded, and the stream is continued at the next
/// <tt>word32</tt> boundary from the state array.
void DiscardBytes(size_t n)
{
for(size_t i=0; i < RoundUpToMultipleOf(n, 4U); i++)
NextMersenneWord();
}
protected:
void Reset(word32 seed)
{
m_idx = N;
m_state[0] = seed;
for (unsigned int i = 1; i < N+1; i++)
m_state[i] = word32(F * (m_state[i-1] ^ (m_state[i-1] >> 30)) + i);
}
/// \brief Returns the next 32-bit word from the state array
/// \return the next 32-bit word from the state array
/// \details fetches the next word frm the state array, performs bit operations on
/// it, and then returns the value to the caller.
word32 NextMersenneWord()
{
if (m_idx >= N) { Twist(); }
word32 temp = m_state[m_idx++];
temp ^= (temp >> 11);
temp ^= (temp << 7) & 0x9D2C5680; // 0x9D2C5680 (2636928640)
temp ^= (temp << 15) & 0xEFC60000; // 0xEFC60000 (4022730752)
return temp ^ (temp >> 18);
}
/// \brief Performs the twist operaton on the state array
void Twist()
{
static const word32 magic[2]={0x0UL, K};
word32 kk, temp;
CRYPTOPP_ASSERT(N >= M);
for (kk=0;kk<N-M;kk++)
{
temp = (m_state[kk] & 0x80000000)|(m_state[kk+1] & 0x7FFFFFFF);
m_state[kk] = m_state[kk+M] ^ (temp >> 1) ^ magic[temp & 0x1UL];
}
for (;kk<N-1;kk++)
{
temp = (m_state[kk] & 0x80000000)|(m_state[kk+1] & 0x7FFFFFFF);
m_state[kk] = m_state[kk+(M-N)] ^ (temp >> 1) ^ magic[temp & 0x1UL];
}
temp = (m_state[N-1] & 0x80000000)|(m_state[0] & 0x7FFFFFFF);
m_state[N-1] = m_state[M-1] ^ (temp >> 1) ^ magic[temp & 0x1UL];
// Reset index
m_idx = 0;
// Wipe temp
SecureWipeArray(&temp, 1);
}
private:
/// \brief 32-bit word state array of size N
FixedSizeSecBlock<word32, N+1> m_state;
/// \brief the current index into the state array
word32 m_idx;
};
/// \brief Original MT19937 generator provided in the ACM paper.
/// \details MT19937 uses 4537 as default initial seed.
/// \details You should reseed the generator after a fork() to avoid multiple generators
/// with the same internal state.
/// \sa MT19937ar, <A HREF="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/ARTICLES/mt.pdf">Mersenne twister:
/// a 623-dimensionally equidistributed uniform pseudo-random number generator</A>
/// \since Crypto++ 5.6.3
#if CRYPTOPP_DOXYGEN_PROCESSING
class MT19937 : public MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x10DCD /*69069*/, 4537> {};
#else
typedef MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x10DCD /*69069*/, 4537> MT19937;
#endif
/// \brief Updated MT19937 generator adapted to provide an array for initialization.
/// \details MT19937 uses 5489 as default initial seed. Use this generator when interoperating with C++11's
/// mt19937 class.
/// \details You should reseed the generator after a fork() to avoid multiple generators
/// with the same internal state.
/// \sa MT19937, <A HREF="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html">Mersenne Twister
/// with improved initialization</A>
/// \since Crypto++ 5.6.3
#if CRYPTOPP_DOXYGEN_PROCESSING
class MT19937ar : public MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x6C078965 /*1812433253*/, 5489> {};
#else
typedef MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x6C078965 /*1812433253*/, 5489> MT19937ar;
#endif
NAMESPACE_END
#endif // CRYPTOPP_MERSENNE_TWISTER_H
FixedSizeSecBlock
Fixed size stack-based SecBlock.
Definition: secblock.h:1246
MT19937
Original MT19937 generator provided in the ACM paper.
Definition: mersenne.h:210
MT19937ar
Updated MT19937 generator adapted to provide an array for initialization.
Definition: mersenne.h:224
MersenneTwister
Mersenne Twister class for Monte-Carlo simulations.
Definition: mersenne.h:32
MersenneTwister::IncorporateEntropy
void IncorporateEntropy(const byte *input, size_t length)
Update RNG state with additional unpredictable values.
Definition: mersenne.h:54
MersenneTwister::GenerateBlock
void GenerateBlock(byte *output, size_t size)
Generate random array of bytes.
Definition: mersenne.h:79
MersenneTwister::DiscardBytes
void DiscardBytes(size_t n)
Generate and discard n bytes.
Definition: mersenne.h:131
MersenneTwister::CanIncorporateEntropy
bool CanIncorporateEntropy() const
Determines if a generator can accept additional entropy.
Definition: mersenne.h:47
MersenneTwister::MersenneTwister
MersenneTwister(word32 seed=S)
Construct a Mersenne Twister.
Definition: mersenne.h:42
MersenneTwister::GenerateWord32
word32 GenerateWord32(word32 min=0, word32 max=0xffffffffL)
Generate a random 32-bit word in the range min to max, inclusive.
Definition: mersenne.h:109
RandomNumberGenerator
Interface for random number generators.
Definition: cryptlib.h:1435
word32
unsigned int word32
32-bit unsigned datatype
Definition: config_int.h:62
cryptlib.h
Abstract base classes that provide a uniform interface to this library.
misc.h
Utility functions for the Crypto++ library.
BitPrecision
unsigned int BitPrecision(const T &value)
Returns the number of bits required for a value.
Definition: misc.h:842
SecureWipeArray
void SecureWipeArray(T *buf, size_t n)
Sets each element of an array to 0.
Definition: misc.h:1490
RoundUpToMultipleOf
T1 RoundUpToMultipleOf(const T1 &n, const T2 &m)
Rounds a value up to a multiple of a second value.
Definition: misc.h:1174
Crop
T Crop(T value, size_t bits)
Truncates the value to the specified number of bits.
Definition: misc.h:926
CryptoPP
Crypto++ library namespace.
secblock.h
Classes and functions for secure memory allocations.
CRYPTOPP_ASSERT
#define CRYPTOPP_ASSERT(exp)
Debugging and diagnostic assertion.
Definition: trap.h:68