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/*
* CTR-BE Mode Cipher
* (C) 1999-2009 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/ctr.h>
#include <botan/xor_buf.h>
namespace Botan {
/*
* CTR-BE Constructor
*/
CTR_BE::CTR_BE(BlockCipher* ciph) :
StreamCipher(ciph->MINIMUM_KEYLENGTH,
ciph->MAXIMUM_KEYLENGTH,
ciph->KEYLENGTH_MULTIPLE),
permutation(ciph)
{
position = 0;
counter.create(permutation->BLOCK_SIZE * BOTAN_PARALLEL_BLOCKS_CTR);
buffer.create(permutation->BLOCK_SIZE * BOTAN_PARALLEL_BLOCKS_CTR);
}
/*
* CTR_BE Destructor
*/
CTR_BE::~CTR_BE()
{
delete permutation;
}
/*
* Zeroize
*/
void CTR_BE::clear() throw()
{
permutation->clear();
buffer.clear();
counter.clear();
position = 0;
}
/*
* Set the key
*/
void CTR_BE::key_schedule(const byte key[], u32bit key_len)
{
permutation->set_key(key, key_len);
// Set a default all-zeros IV
set_iv(0, 0);
}
/*
* Return the name of this type
*/
std::string CTR_BE::name() const
{
return ("CTR-BE(" + permutation->name() + ")");
}
/*
* CTR-BE Encryption/Decryption
*/
void CTR_BE::cipher(const byte in[], byte out[], u32bit length)
{
while(length >= buffer.size() - position)
{
xor_buf(out, in, buffer.begin() + position, buffer.size() - position);
length -= (buffer.size() - position);
in += (buffer.size() - position);
out += (buffer.size() - position);
increment_counter();
}
xor_buf(out, in, buffer.begin() + position, length);
position += length;
}
/*
* Set CTR-BE IV
*/
void CTR_BE::set_iv(const byte iv[], u32bit iv_len)
{
if(!valid_iv_length(iv_len))
throw Invalid_IV_Length(name(), iv_len);
const u32bit BLOCK_SIZE = permutation->BLOCK_SIZE;
counter.clear();
counter.copy(0, iv, iv_len);
const u32bit PARALLEL_BLOCKS = counter.size() / BLOCK_SIZE;
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;
}
permutation->encrypt_n(counter, buffer, PARALLEL_BLOCKS);
position = 0;
}
/*
* Increment the counter and update the buffer
*/
void CTR_BE::increment_counter()
{
const u32bit PARALLEL_BLOCKS = counter.size() / permutation->BLOCK_SIZE;
for(u32bit i = 0; i != PARALLEL_BLOCKS; ++i)
{
byte* this_ctr = counter + i*permutation->BLOCK_SIZE;
byte last_byte = this_ctr[permutation->BLOCK_SIZE-1];
last_byte += PARALLEL_BLOCKS;
if(this_ctr[permutation->BLOCK_SIZE-1] > last_byte)
for(s32bit j = permutation->BLOCK_SIZE - 2; j >= 0; --j)
if(++this_ctr[j])
break;
this_ctr[permutation->BLOCK_SIZE-1] = last_byte;
}
permutation->encrypt_n(counter, buffer, PARALLEL_BLOCKS);
position = 0;
}
}
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