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/*
* CFB Mode
* (C) 1999-2007,2013,2017 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/cfb.h>
namespace Botan {
CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :
m_cipher(cipher),
m_block_size(m_cipher->block_size()),
m_feedback_bytes(feedback_bits ? feedback_bits / 8 : m_block_size)
{
if(feedback_bits % 8 || feedback() > cipher->block_size())
throw Invalid_Argument(name() + ": feedback bits " +
std::to_string(feedback_bits) + " not supported");
}
void CFB_Mode::clear()
{
m_cipher->clear();
m_keystream.clear();
reset();
}
void CFB_Mode::reset()
{
m_state.clear();
zeroise(m_keystream);
}
std::string CFB_Mode::name() const
{
if(feedback() == cipher().block_size())
return cipher().name() + "/CFB";
else
return cipher().name() + "/CFB(" + std::to_string(feedback()*8) + ")";
}
size_t CFB_Mode::output_length(size_t input_length) const
{
return input_length;
}
size_t CFB_Mode::update_granularity() const
{
return feedback();
}
size_t CFB_Mode::minimum_final_size() const
{
return 0;
}
Key_Length_Specification CFB_Mode::key_spec() const
{
return cipher().key_spec();
}
size_t CFB_Mode::default_nonce_length() const
{
return block_size();
}
bool CFB_Mode::valid_nonce_length(size_t n) const
{
return (n == 0 || n == block_size());
}
void CFB_Mode::key_schedule(const uint8_t key[], size_t length)
{
m_cipher->set_key(key, length);
m_keystream.resize(m_cipher->block_size());
}
void CFB_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
verify_key_set(m_keystream.size());
if(nonce_len == 0)
{
if(m_state.empty())
{
throw Invalid_State("CFB requires a non-empty initial nonce");
}
// No reason to encrypt state->keystream_buf, because no change
}
else
{
m_state.assign(nonce, nonce + nonce_len);
cipher().encrypt(m_state, m_keystream);
m_keystream_pos = 0;
}
}
void CFB_Mode::shift_register()
{
const size_t shift = feedback();
const size_t carryover = block_size() - shift;
if(carryover > 0)
{
copy_mem(m_state.data(), &m_state[shift], carryover);
}
copy_mem(&m_state[carryover], m_keystream.data(), shift);
cipher().encrypt(m_state, m_keystream);
m_keystream_pos = 0;
}
size_t CFB_Encryption::process(uint8_t buf[], size_t sz)
{
verify_key_set(m_keystream.size());
BOTAN_STATE_CHECK(m_state.empty() == false);
const size_t shift = feedback();
size_t left = sz;
if(m_keystream_pos != 0)
{
const size_t take = std::min<size_t>(left, shift - m_keystream_pos);
xor_buf(m_keystream.data() + m_keystream_pos, buf, take);
copy_mem(buf, m_keystream.data() + m_keystream_pos, take);
m_keystream_pos += take;
left -= take;
buf += take;
if(m_keystream_pos == shift)
{
shift_register();
}
}
while(left >= shift)
{
xor_buf(m_keystream.data(), buf, shift);
copy_mem(buf, m_keystream.data(), shift);
left -= shift;
buf += shift;
shift_register();
}
if(left > 0)
{
xor_buf(m_keystream.data(), buf, left);
copy_mem(buf, m_keystream.data(), left);
m_keystream_pos += left;
}
return sz;
}
void CFB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
update(buffer, offset);
}
namespace {
inline void xor_copy(uint8_t buf[], uint8_t key_buf[], size_t len)
{
for(size_t i = 0; i != len; ++i)
{
uint8_t k = key_buf[i];
key_buf[i] = buf[i];
buf[i] ^= k;
}
}
}
size_t CFB_Decryption::process(uint8_t buf[], size_t sz)
{
verify_key_set(m_keystream.size());
BOTAN_STATE_CHECK(m_state.empty() == false);
const size_t shift = feedback();
size_t left = sz;
if(m_keystream_pos != 0)
{
const size_t take = std::min<size_t>(left, shift - m_keystream_pos);
xor_copy(buf, m_keystream.data() + m_keystream_pos, take);
m_keystream_pos += take;
left -= take;
buf += take;
if(m_keystream_pos == shift)
{
shift_register();
}
}
while(left >= shift)
{
xor_copy(buf, m_keystream.data(), shift);
left -= shift;
buf += shift;
shift_register();
}
if(left > 0)
{
xor_copy(buf, m_keystream.data(), left);
m_keystream_pos += left;
}
return sz;
}
void CFB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
{
update(buffer, offset);
}
}
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