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/*
* Counter mode
* (C) 1999-2011,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/ctr.h>
namespace Botan {
CTR_BE::CTR_BE(BlockCipher* ciph) :
m_cipher(ciph),
m_counter(m_cipher->parallel_bytes()),
m_pad(m_counter.size()),
m_iv(m_cipher->block_size()),
m_block_size(m_cipher->block_size()),
m_ctr_size(m_block_size),
m_pad_pos(0)
{
}
CTR_BE::CTR_BE(BlockCipher* cipher, size_t ctr_size) :
m_cipher(cipher),
m_counter(m_cipher->parallel_bytes()),
m_pad(m_counter.size()),
m_iv(m_cipher->block_size()),
m_block_size(m_cipher->block_size()),
m_ctr_size(ctr_size),
m_pad_pos(0)
{
if(m_ctr_size == 0 || m_ctr_size > m_block_size)
throw Invalid_Argument("Invalid CTR-BE counter size");
}
void CTR_BE::clear()
{
m_cipher->clear();
zeroise(m_pad);
zeroise(m_counter);
zeroise(m_iv);
m_pad_pos = 0;
}
void CTR_BE::key_schedule(const uint8_t key[], size_t key_len)
{
m_cipher->set_key(key, key_len);
// Set a default all-zeros IV
set_iv(nullptr, 0);
}
std::string CTR_BE::name() const
{
return ("CTR-BE(" + m_cipher->name() + ")");
}
void CTR_BE::cipher(const uint8_t in[], uint8_t out[], size_t length)
{
while(length >= m_pad.size() - m_pad_pos)
{
xor_buf(out, in, &m_pad[m_pad_pos], m_pad.size() - m_pad_pos);
length -= (m_pad.size() - m_pad_pos);
in += (m_pad.size() - m_pad_pos);
out += (m_pad.size() - m_pad_pos);
increment_counter();
}
xor_buf(out, in, &m_pad[m_pad_pos], length);
m_pad_pos += length;
}
void CTR_BE::set_iv(const uint8_t iv[], size_t iv_len)
{
if(!valid_iv_length(iv_len))
throw Invalid_IV_Length(name(), iv_len);
zeroise(m_iv);
buffer_insert(m_iv, 0, iv, iv_len);
seek(0);
}
/*
* Increment the counter and update the buffer
*/
void CTR_BE::increment_counter()
{
const size_t n_wide = m_counter.size() / m_block_size;
add_counter(n_wide);
m_cipher->encrypt_n(m_counter.data(), m_pad.data(), n_wide);
m_pad_pos = 0;
}
void CTR_BE::add_counter(const uint64_t counter)
{
const size_t n_wide = m_counter.size() / m_block_size;
for(size_t i = 0; i != n_wide; ++i)
{
uint64_t local_counter = counter;
uint16_t carry = static_cast<uint8_t>(local_counter);
for(size_t j = 0; (carry || local_counter) && j != m_ctr_size; ++j)
{
const size_t off = i*m_block_size + (m_block_size-1-j);
const uint16_t cnt = static_cast<uint16_t>(m_counter[off]) + carry;
m_counter[off] = static_cast<uint8_t>(cnt);
local_counter = (local_counter >> 8);
carry = (cnt >> 8) + static_cast<uint8_t>(local_counter);
}
}
}
void CTR_BE::seek(uint64_t offset)
{
const size_t n_wide = m_counter.size() / m_block_size;
const uint64_t base_counter = n_wide * (offset / m_counter.size());
zeroise(m_counter);
buffer_insert(m_counter, 0, m_iv);
// Set m_counter blocks to IV, IV + 1, ... IV + n
for(size_t i = 1; i != n_wide; ++i)
{
buffer_insert(m_counter,
i*m_block_size,
&m_counter[(i-1)*m_block_size],
m_block_size);
for(size_t j = 0; j != m_ctr_size; ++j)
if(++m_counter[i*m_block_size + (m_block_size - 1 - j)])
break;
}
if (base_counter > 0)
add_counter(base_counter);
m_cipher->encrypt_n(m_counter.data(), m_pad.data(), n_wide);
m_pad_pos = offset % m_counter.size();
}
}
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