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/*
* CTR Mode
* (C) 1999-2009 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/ctr.h>
#include <botan/xor_buf.h>
#include <algorithm>
namespace Botan {
namespace {
const u32bit PARALLEL_BLOCKS = BOTAN_PARALLEL_BLOCKS_CTR;
}
/*
* CTR-BE Constructor
*/
CTR_BE::CTR_BE(BlockCipher* ciph) : cipher(ciph)
{
position = 0;
counter.create(ciph->BLOCK_SIZE * PARALLEL_BLOCKS);
enc_buffer.create(ciph->BLOCK_SIZE * PARALLEL_BLOCKS);
}
/*
* CTR-BE Constructor
*/
CTR_BE::CTR_BE(BlockCipher* ciph, const SymmetricKey& key,
const InitializationVector& iv) :
cipher(ciph)
{
position = 0;
counter.create(ciph->BLOCK_SIZE * PARALLEL_BLOCKS);
enc_buffer.create(ciph->BLOCK_SIZE * PARALLEL_BLOCKS);
cipher->set_key(key);
set_iv(iv);
}
/*
* CTR_BE Destructor
*/
CTR_BE::~CTR_BE()
{
delete cipher;
}
/*
* Return the name of this type
*/
std::string CTR_BE::name() const
{
return ("CTR-BE/" + cipher->name());
}
/*
* Set CTR-BE IV
*/
void CTR_BE::set_iv(const InitializationVector& iv)
{
const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
if(iv.length() != BLOCK_SIZE)
throw Invalid_IV_Length(name(), iv.length());
enc_buffer.clear();
position = 0;
counter.copy(0, iv.begin(), iv.length());
for(u32bit i = 1; i != PARALLEL_BLOCKS; ++i)
{
counter.copy(i*BLOCK_SIZE,
counter.begin() + (i-1)*BLOCK_SIZE, BLOCK_SIZE);
for(s32bit j = BLOCK_SIZE - 1; j >= 0; --j)
if(++counter[i*BLOCK_SIZE+j])
break;
}
cipher->encrypt_n(counter, enc_buffer, PARALLEL_BLOCKS);
}
/*
* CTR-BE Encryption/Decryption
*/
void CTR_BE::write(const byte input[], u32bit length)
{
u32bit copied = std::min(enc_buffer.size() - position, length);
xor_buf(enc_buffer + position, input, copied);
send(enc_buffer + position, copied);
input += copied;
length -= copied;
position += copied;
if(position == enc_buffer.size())
increment_counter();
while(length >= enc_buffer.size())
{
xor_buf(enc_buffer, input, enc_buffer.size());
send(enc_buffer, enc_buffer.size());
input += enc_buffer.size();
length -= enc_buffer.size();
increment_counter();
}
xor_buf(enc_buffer + position, input, length);
send(enc_buffer + position, length);
position += length;
}
/*
* Increment the counter and update the buffer
*/
void CTR_BE::increment_counter()
{
for(u32bit i = 0; i != PARALLEL_BLOCKS; ++i)
{
byte* this_ctr = counter + i*cipher->BLOCK_SIZE;
byte last_byte = this_ctr[cipher->BLOCK_SIZE-1];
last_byte += PARALLEL_BLOCKS;
if(this_ctr[cipher->BLOCK_SIZE-1] > last_byte)
for(s32bit j = cipher->BLOCK_SIZE - 2; j >= 0; --j)
if(++this_ctr[j])
break;
this_ctr[cipher->BLOCK_SIZE-1] = last_byte;
}
cipher->encrypt_n(counter, enc_buffer, PARALLEL_BLOCKS);
position = 0;
}
}
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