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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>
#include <botan/loadstor.h>
namespace Botan {
CTR_BE::CTR_BE(BlockCipher* ciph) :
m_cipher(ciph),
m_block_size(m_cipher->block_size()),
m_ctr_size(m_block_size),
m_ctr_blocks(m_cipher->parallel_bytes() / m_block_size),
m_counter(m_cipher->parallel_bytes()),
m_pad(m_counter.size()),
m_iv(m_cipher->block_size()),
m_pad_pos(0)
{
}
CTR_BE::CTR_BE(BlockCipher* cipher, size_t ctr_size) :
m_cipher(cipher),
m_block_size(m_cipher->block_size()),
m_ctr_size(ctr_size),
m_ctr_blocks(m_cipher->parallel_bytes() / m_block_size),
m_counter(m_cipher->parallel_bytes()),
m_pad(m_counter.size()),
m_iv(m_cipher->block_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)
{
const uint8_t* pad_bits = &m_pad[0];
const size_t pad_size = m_pad.size();
if(m_pad_pos > 0)
{
const size_t avail = pad_size - m_pad_pos;
const size_t take = std::min(length, avail);
xor_buf(out, in, pad_bits + m_pad_pos, take);
length -= take;
in += take;
out += take;
m_pad_pos += take;
if(take == avail)
{
add_counter(m_ctr_blocks);
m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
m_pad_pos = 0;
}
}
while(length >= pad_size)
{
xor_buf(out, in, pad_bits, pad_size);
length -= pad_size;
in += pad_size;
out += pad_size;
add_counter(m_ctr_blocks);
m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
}
xor_buf(out, in, pad_bits, 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);
}
void CTR_BE::add_counter(const uint64_t counter)
{
const size_t ctr_size = m_ctr_size;
const size_t ctr_blocks = m_ctr_blocks;
const size_t BS = m_block_size;
if(ctr_size == 4)
{
size_t off = (BS - 4);
for(size_t i = 0; i != ctr_blocks; ++i)
{
uint32_t low32 = load_be<uint32_t>(&m_counter[off], 0);
low32 += counter;
store_be(low32, &m_counter[off]);
off += BS;
}
}
else if(ctr_size == 8)
{
size_t off = (BS - 8);
for(size_t i = 0; i != ctr_blocks; ++i)
{
uint64_t low64 = load_be<uint64_t>(&m_counter[off], 0);
low64 += counter;
store_be(low64, &m_counter[off]);
off += BS;
}
}
else if(ctr_size == 16)
{
size_t off = (BS - 16);
for(size_t i = 0; i != ctr_blocks; ++i)
{
uint64_t b0 = load_be<uint64_t>(&m_counter[off], 0);
uint64_t b1 = load_be<uint64_t>(&m_counter[off], 1);
b1 += counter;
b1 += (b1 < counter); // carry
store_be(b0, &m_counter[off]);
store_be(b1, &m_counter[off+8]);
off += BS;
}
}
else
{
for(size_t i = 0; i != ctr_blocks; ++i)
{
uint64_t local_counter = counter;
uint16_t carry = static_cast<uint8_t>(local_counter);
for(size_t j = 0; (carry || local_counter) && j != ctr_size; ++j)
{
const size_t off = i*BS + (BS-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 uint64_t base_counter = m_ctr_blocks * (offset / m_counter.size());
zeroise(m_counter);
buffer_insert(m_counter, 0, m_iv);
const size_t BS = m_block_size;
// Set m_counter blocks to IV, IV + 1, ... IV + n
for(size_t i = 1; i != m_ctr_blocks; ++i)
{
buffer_insert(m_counter, i*BS, &m_counter[(i-1)*BS], BS);
for(size_t j = 0; j != m_ctr_size; ++j)
if(++m_counter[i*BS + (BS - 1 - j)])
break;
}
if(base_counter > 0)
add_counter(base_counter);
m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);
m_pad_pos = offset % m_counter.size();
}
}
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