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/*
* CFB Mode
* (C) 1999-2007,2013 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/cfb.h>
#include <botan/parsing.h>
namespace Botan {
CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :
m_cipher(cipher),
m_feedback_bytes(feedback_bits ? feedback_bits / 8 : cipher->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();
reset();
}
void CFB_Mode::reset()
{
m_shift_register.clear();
m_keystream_buf.clear();
}
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 cipher().block_size();
}
bool CFB_Mode::valid_nonce_length(size_t n) const
{
return (n == cipher().block_size());
}
void CFB_Mode::key_schedule(const byte key[], size_t length)
{
m_cipher->set_key(key, length);
}
void CFB_Mode::start_msg(const byte nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
m_shift_register.assign(nonce, nonce + nonce_len);
m_keystream_buf.resize(m_shift_register.size());
cipher().encrypt(m_shift_register, m_keystream_buf);
}
size_t CFB_Encryption::process(uint8_t buf[], size_t sz)
{
const size_t BS = cipher().block_size();
secure_vector<byte>& state = shift_register();
const size_t shift = feedback();
size_t left = sz;
while(left)
{
const size_t took = std::min(shift, left);
xor_buf(buf, &keystream_buf()[0], took);
// Assumes feedback-sized block except for last input
if (BS - shift > 0)
{
copy_mem(state.data(), &state[shift], BS - shift);
}
copy_mem(&state[BS-shift], buf, took);
cipher().encrypt(state, keystream_buf());
buf += took;
left -= took;
}
return sz;
}
void CFB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
{
update(buffer, offset);
}
size_t CFB_Decryption::process(uint8_t buf[], size_t sz)
{
const size_t BS = cipher().block_size();
secure_vector<byte>& state = shift_register();
const size_t shift = feedback();
size_t left = sz;
while(left)
{
const size_t took = std::min(shift, left);
// first update shift register with ciphertext
if (BS - shift > 0)
{
copy_mem(state.data(), &state[shift], BS - shift);
}
copy_mem(&state[BS-shift], buf, took);
// then decrypt
xor_buf(buf, &keystream_buf()[0], took);
// then update keystream
cipher().encrypt(state, keystream_buf());
buf += took;
left -= took;
}
return sz;
}
void CFB_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
{
update(buffer, offset);
}
}
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