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rng.cpp

// rng.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "rng.h"

#include <time.h>
#include <math.h>

NAMESPACE_BEGIN(CryptoPP)

// linear congruential generator
// originally by William S. England

// do not use for cryptographic purposes

/*
** Original_numbers are the original published m and q in the
** ACM article above.  John Burton has furnished numbers for
** a reportedly better generator.  The new numbers are now
** used in this program by default.
*/

#ifndef LCRNG_ORIGINAL_NUMBERS
const word32 LC_RNG::m=2147483647L;
const word32 LC_RNG::q=44488L;

const word16 LC_RNG::a=(unsigned int)48271L;
const word16 LC_RNG::r=3399;
#else
const word32 LC_RNG::m=2147483647L;
const word32 LC_RNG::q=127773L;

const word16 LC_RNG::a=16807;
const word16 LC_RNG::r=2836;
#endif

byte LC_RNG::GenerateByte()
{
        word32 hi = seed/q;
        word32 lo = seed%q;

        long test = a*lo - r*hi;

        if (test > 0)
                seed = test;
        else
                seed = test+ m;

        return (seedBytes[0] ^ seedBytes[1] ^ seedBytes[2] ^ seedBytes[3]);
}

// ********************************************************

X917RNG::X917RNG(BlockTransformation *c, const byte *seed)
        : cipher(c),
          S(cipher->BlockSize()),
          dtbuf(S),
          randseed(seed, S),
          randbuf(S),
          randbuf_counter(0)
{
        time_t tstamp1 = time(0);
        xorbuf(dtbuf, (byte *)&tstamp1, STDMIN((int)sizeof(tstamp1), S));
        cipher->ProcessBlock(dtbuf);
        clock_t tstamp2 = clock();
        xorbuf(dtbuf, (byte *)&tstamp2, STDMIN((int)sizeof(tstamp2), S));
        cipher->ProcessBlock(dtbuf);
}

byte X917RNG::GenerateByte()
{
        if (randbuf_counter==0)
        {
                // calculate new enciphered timestamp
                clock_t tstamp = clock();
                xorbuf(dtbuf, (byte *)&tstamp, STDMIN((int)sizeof(tstamp), S));
                cipher->ProcessBlock(dtbuf);

                // combine enciphered timestamp with seed
                xorbuf(randseed, dtbuf, S);

                // generate a new block of random bytes
                cipher->ProcessBlock(randseed, randbuf);

                // compute new seed vector
                for (int i=0; i<S; i++)
                        randseed[i] = randbuf[i] ^ dtbuf[i];
                cipher->ProcessBlock(randseed);

                randbuf_counter=S;
        }
        return(randbuf[--randbuf_counter]);
}

MaurerRandomnessTest::MaurerRandomnessTest()
        : sum(0.0), n(0)
{
        for (unsigned i=0; i<V; i++)
                tab[i] = 0;
}

inline void MaurerRandomnessTest::Put(byte inByte)
{
        if (n >= Q)
                sum += log(double(n - tab[inByte]));
        tab[inByte] = n;
        n++;
}

void MaurerRandomnessTest::Put(const byte *inString, unsigned int length)
{
        while (length--)
                Put(*inString++);
}

double MaurerRandomnessTest::GetTestValue() const
{
        double fTu = (sum/(n-Q))/log(2.0);      // this is the test value defined by Maurer

        double value = fTu * 0.1392;            // arbitrarily normalize it to
        return value > 1.0 ? 1.0 : value;       // a number between 0 and 1
}

NAMESPACE_END

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