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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/internal/stream_utils.h>
#include <botan/ctr.h>
namespace Botan {
BOTAN_REGISTER_NAMED_T(StreamCipher, "CTR-BE", CTR_BE, CTR_BE::make);
CTR_BE* CTR_BE::make(const Spec& spec)
{
if(spec.algo_name() == "CTR-BE" && spec.arg_count() == 1)
{
if(BlockCipher* c = Algo_Registry<BlockCipher>::global_registry().make(spec.arg(0)))
return new CTR_BE(c);
}
return nullptr;
}
CTR_BE::CTR_BE(BlockCipher* ciph) :
m_cipher(ciph),
m_counter(256 * m_cipher->block_size()),
m_pad(m_counter.size()),
m_pad_pos(0)
{
}
void CTR_BE::clear()
{
m_cipher->clear();
zeroise(m_pad);
zeroise(m_counter);
m_pad_pos = 0;
}
void CTR_BE::key_schedule(const byte 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 byte in[], byte 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 byte iv[], size_t iv_len)
{
if(!valid_iv_length(iv_len))
throw Invalid_IV_Length(name(), iv_len);
const size_t bs = m_cipher->block_size();
zeroise(m_counter);
buffer_insert(m_counter, 0, iv, iv_len);
// Set m_counter blocks to IV, IV + 1, ... IV + 255
for(size_t i = 1; i != 256; ++i)
{
buffer_insert(m_counter, i*bs, &m_counter[(i-1)*bs], bs);
for(size_t j = 0; j != bs; ++j)
if(++m_counter[i*bs + (bs - 1 - j)])
break;
}
m_cipher->encrypt_n(&m_counter[0], &m_pad[0], 256);
m_pad_pos = 0;
}
/*
* Increment the counter and update the buffer
*/
void CTR_BE::increment_counter()
{
const size_t bs = m_cipher->block_size();
/*
* Each counter value always needs to be incremented by 256,
* so we don't touch the lowest byte and instead treat it as
* an increment of one starting with the next byte.
*/
for(size_t i = 0; i != 256; ++i)
{
for(size_t j = 1; j != bs; ++j)
if(++m_counter[i*bs + (bs - 1 - j)])
break;
}
m_cipher->encrypt_n(&m_counter[0], &m_pad[0], 256);
m_pad_pos = 0;
}
}
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