randpool.cpp

// randpool.cpp - originally written and placed in the public domain by Wei Dai
// RandomPool used to follow the design of randpool in PGP 2.6.x,
// but as of version 5.5 it has been redesigned to reduce the risk
// of reusing random numbers after state rollback (which may occur
// when running in a virtual machine like VMware).
 
#include "pch.h"
 
#ifndef CRYPTOPP_IMPORTS
 
#include "randpool.h"
#include "aes.h"
#include "sha.h"
#include "hrtimer.h"
#include "trap.h"
 
// OldRandomPool
#include "mdc.h"
#include "modes.h"
 
#include <time.h>
 
NAMESPACE_BEGIN(CryptoPP)
 
RandomPool::RandomPool()
    : m_pCipher(new AES::Encryption), m_keySet(false)
{
    std::memset(m_key, 0, m_key.SizeInBytes());
    std::memset(m_seed, 0, m_seed.SizeInBytes());
}
 
void RandomPool::IncorporateEntropy(const byte *input, size_t length)
{
    SHA256 hash;
    hash.Update(m_key, 32);
    hash.Update(input, length);
    hash.Final(m_key);
    m_keySet = false;
}
 
void RandomPool::GenerateIntoBufferedTransformation(BufferedTransformation &target, const std::string &channel, lword size)
{
    if (size > 0)
    {
        if (!m_keySet)
            m_pCipher->SetKey(m_key, 32);
 
        CRYPTOPP_COMPILE_ASSERT(sizeof(TimerWord) <= 16);
        CRYPTOPP_COMPILE_ASSERT(sizeof(time_t) <= 8);
 
        Timer timer;
        TimerWord tw = timer.GetCurrentTimerValue();
 
        *(TimerWord *)(void*)m_seed.data() += tw;
        time_t t = time(NULLPTR);
 
        // UBsan finding: signed integer overflow: 1876017710 + 1446085457 cannot be represented in type 'long int'
        // *(time_t *)(m_seed.data()+8) += t;
        word64 tt1 = 0, tt2 = (word64)t;
        std::memcpy(&tt1, m_seed.data()+8, 8);
        std::memcpy(m_seed.data()+8, &(tt2 += tt1), 8);
 
        // Wipe the intermediates
        *((volatile TimerWord*)&tw) = 0;
        *((volatile word64*)&tt1) = 0;
        *((volatile word64*)&tt2) = 0;
 
        do
        {
            m_pCipher->ProcessBlock(m_seed);
            size_t len = UnsignedMin(16, size);
            target.ChannelPut(channel, m_seed, len);
            size -= len;
        } while (size > 0);
    }
}
 
// OldRandomPool is provided for backwards compatibility for a migration path
typedef MDC<SHA1> OldRandomPoolCipher;
 
OldRandomPool::OldRandomPool(unsigned int poolSize)
        : pool(poolSize), key(OldRandomPoolCipher::DEFAULT_KEYLENGTH), addPos(0), getPos(poolSize)
{
    CRYPTOPP_ASSERT(poolSize > key.size());
    std::memset(pool, 0, poolSize);
    std::memset(key, 0, key.size());
}
 
void OldRandomPool::IncorporateEntropy(const byte *input, size_t length)
{
    size_t t;
    while (length > (t = pool.size() - addPos))
    {
        xorbuf(pool+addPos, input, t);
        input += t;
        length -= t;
        Stir();
    }
 
    if (length)
    {
        xorbuf(pool+addPos, input, length);
        addPos += length;
        getPos = pool.size(); // Force stir on get
    }
}
 
// GenerateWord32 is overridden and provides Crypto++ 5.4 behavior.
// Taken from RandomNumberGenerator::GenerateWord32 in cryptlib.cpp.
word32 OldRandomPool::GenerateWord32 (word32 min, word32 max)
{
    const word32 range = max-min;
    const unsigned int maxBytes = BytePrecision(range);
    const unsigned int maxBits = BitPrecision(range);
 
    word32 value;
 
    do
    {
        value = 0;
        for (unsigned int i=0; i<maxBytes; i++)
            value = (value << 8) | GenerateByte();
 
        value = Crop(value, maxBits);
    } while (value > range);
 
    return value+min;
}
 
void OldRandomPool::Stir()
{
    CFB_Mode<OldRandomPoolCipher>::Encryption cipher;
 
    for (int i=0; i<2; i++)
    {
        cipher.SetKeyWithIV(key, key.size(), pool.end()-cipher.IVSize());
        cipher.ProcessString(pool, pool.size());
        std::memcpy(key, pool, key.size());
    }
 
    addPos = 0;
    getPos = key.size();
}
 
void OldRandomPool::GenerateIntoBufferedTransformation(BufferedTransformation &target, const std::string &channel, lword size)
{
    while (size > 0)
    {
        if (getPos == pool.size())
                Stir();
        size_t t = UnsignedMin(pool.size() - getPos, size);
        target.ChannelPut(channel, pool+getPos, t);
        size -= t;
        getPos += t;
    }
}
 
byte OldRandomPool::GenerateByte()
{
    if (getPos == pool.size())
        Stir();
 
    return pool[getPos++];
}
 
void OldRandomPool::GenerateBlock(byte *outString, size_t size)
{
    ArraySink sink(outString, size);
    GenerateIntoBufferedTransformation(sink, DEFAULT_CHANNEL, size);
}
 
NAMESPACE_END
 
#endif