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randpool.cpp

// randpool.cpp - written and placed in the public domain by Wei Dai
// The algorithm in this module comes from PGP's randpool.c

#include "pch.h"
#include "randpool.h"
#include "mdc.h"
#include "sha.h"
#include "modes.h"

NAMESPACE_BEGIN(CryptoPP)

typedef MDC<SHA> RandomPoolCipher;

RandomPool::RandomPool(unsigned int poolSize)
        : pool(poolSize), key(RandomPoolCipher::DEFAULT_KEYLENGTH)
{
        assert(poolSize > key.size);

        addPos=0;
        getPos=poolSize;
        memset(pool, 0, poolSize);
        memset(key, 0, key.size);
}

void RandomPool::Stir()
{
        for (int i=0; i<2; i++)
        {
                RandomPoolCipher cipher(key);
                CFBEncryption cfb(cipher, pool+pool.size-cipher.BlockSize());
                cfb.ProcessString(pool, pool.size);
                memcpy(key, pool, key.size);
        }

        addPos = 0;
        getPos = key.size;
}

void RandomPool::Put(byte inByte)
{
        if (addPos == pool.size)
                Stir();

        pool[addPos++] ^= inByte;
        getPos = pool.size; // Force stir on get
}

void RandomPool::Put(const byte *inString, unsigned int length)
{
        unsigned t;

        while (length > (t = pool.size - addPos))
        {
                xorbuf(pool+addPos, inString, t);
                inString += t;
                length -= t;
                Stir();
        }

        if (length)
        {
                xorbuf(pool+addPos, inString, length);
                addPos += length;
                getPos = pool.size; // Force stir on get
        }
}

byte RandomPool::GenerateByte()
{
        if (getPos == pool.size)
                Stir();

        return pool[getPos++];
}

void RandomPool::GenerateBlock(byte *outString, unsigned int size)
{
        unsigned t;

        while (size > (t = pool.size - getPos))
        {
                memcpy(outString, pool+getPos, t);
                outString += t;
                size -= t;
                Stir();
        }

        if (size)
        {
                memcpy(outString, pool+getPos, size);
                getPos += size;
        }
}

NAMESPACE_END

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