inline void CTR_ModePolicy::ProcessMultipleBlocks(byte *output, const byte *input, size_t n)
{
unsigned int s = BlockSize(), j = 0;
for (unsigned int i=1; i<n; i++, j+=s)
IncrementCounterByOne(m_counterArray + j + s, m_counterArray + j, s);
m_cipher->ProcessAndXorMultipleBlocks(m_counterArray, input, output, n);
IncrementCounterByOne(m_counterArray, m_counterArray + s*(n-1), s);
}
void CTR_ModePolicy::OperateKeystream(KeystreamOperation operation, byte *output, const byte *input, size_t iterationCount)
{
assert(m_cipher->IsForwardTransformation()); // CTR mode needs the "encrypt" direction of the underlying block cipher, even to decrypt
unsigned int maxBlocks = m_cipher->OptimalNumberOfParallelBlocks();
if (maxBlocks == 1)
{
unsigned int sizeIncrement = BlockSize();
while (iterationCount)
{
m_cipher->ProcessAndXorBlock(m_counterArray, input, output);
IncrementCounterByOne(m_counterArray, sizeIncrement);
output += sizeIncrement;
input += sizeIncrement;
iterationCount -= 1;
}
}
else
{
unsigned int sizeIncrement = maxBlocks * BlockSize();
while (iterationCount >= maxBlocks)
{
ProcessMultipleBlocks(output, input, maxBlocks);
output += sizeIncrement;
input += sizeIncrement;
iterationCount -= maxBlocks;
}
if (iterationCount > 0)
ProcessMultipleBlocks(output, input, iterationCount);
}
}
void CTR_ModePolicy::OperateKeystream(KeystreamOperation operation, byte *output, const byte *input, size_t iterationCount)
{
unsigned int maxBlocks = m_cipher->OptimalNumberOfParallelBlocks();
if (maxBlocks == 1)
{
unsigned int sizeIncrement = BlockSize();
while (iterationCount)
{
m_cipher->ProcessAndXorBlock(m_counterArray, input, output);
IncrementCounterByOne(m_counterArray, sizeIncrement);
output += sizeIncrement;
input += sizeIncrement;
iterationCount -= 1;
}
}
else
{
unsigned int sizeIncrement = maxBlocks * BlockSize();
while (iterationCount >= maxBlocks)
{
ProcessMultipleBlocks(output, input, maxBlocks);
output += sizeIncrement;
input += sizeIncrement;
iterationCount -= maxBlocks;
}
if (iterationCount > 0)
ProcessMultipleBlocks(output, input, iterationCount);
}
}
void CTR_ModePolicy::IncrementCounterBy256()
{
IncrementCounterByOne(m_counterArray, BlockSize()-1);
}
void CTR_ModePolicy::GetNextIV(byte *IV)
{
IncrementCounterByOne(IV, m_counterArray, BlockSize());
}