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/*
* CFB Mode
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/cfb.h>
#include <botan/parsing.h>
#include <botan/xor_buf.h>
#include <algorithm>
namespace Botan {
namespace {
/*
* Check the feedback size
*/
void check_feedback(u32bit BLOCK_SIZE, u32bit FEEDBACK_SIZE, u32bit bits,
const std::string& name)
{
if(FEEDBACK_SIZE == 0 || FEEDBACK_SIZE > BLOCK_SIZE || bits % 8 != 0)
throw Invalid_Argument(name + ": Invalid feedback size " +
to_string(bits));
}
}
/*
* CFB Encryption Constructor
*/
CFB_Encryption::CFB_Encryption(BlockCipher* ciph,
u32bit fback_bits) :
BlockCipherMode(ciph, "CFB", ciph->BLOCK_SIZE, 1),
FEEDBACK_SIZE(fback_bits ? fback_bits / 8: BLOCK_SIZE)
{
check_feedback(BLOCK_SIZE, FEEDBACK_SIZE, fback_bits, name());
}
/*
* CFB Encryption Constructor
*/
CFB_Encryption::CFB_Encryption(BlockCipher* ciph,
const SymmetricKey& key,
const InitializationVector& iv,
u32bit fback_bits) :
BlockCipherMode(ciph, "CFB", ciph->BLOCK_SIZE, 1),
FEEDBACK_SIZE(fback_bits ? fback_bits / 8: BLOCK_SIZE)
{
check_feedback(BLOCK_SIZE, FEEDBACK_SIZE, fback_bits, name());
set_key(key);
set_iv(iv);
}
/*
* Encrypt data in CFB mode
*/
void CFB_Encryption::write(const byte input[], u32bit length)
{
while(length)
{
u32bit xored = std::min(FEEDBACK_SIZE - position, length);
xor_buf(buffer + position, input, xored);
send(buffer + position, xored);
input += xored;
length -= xored;
position += xored;
if(position == FEEDBACK_SIZE)
feedback();
}
}
/*
* Do the feedback
*/
void CFB_Encryption::feedback()
{
for(u32bit j = 0; j != BLOCK_SIZE - FEEDBACK_SIZE; ++j)
state[j] = state[j + FEEDBACK_SIZE];
state.copy(BLOCK_SIZE - FEEDBACK_SIZE, buffer, FEEDBACK_SIZE);
cipher->encrypt(state, buffer);
position = 0;
}
/*
* CFB Decryption Constructor
*/
CFB_Decryption::CFB_Decryption(BlockCipher* ciph,
u32bit fback_bits) :
BlockCipherMode(ciph, "CFB", ciph->BLOCK_SIZE, 1),
FEEDBACK_SIZE(fback_bits ? fback_bits / 8 : BLOCK_SIZE)
{
check_feedback(BLOCK_SIZE, FEEDBACK_SIZE, fback_bits, name());
}
/*
* CFB Decryption Constructor
*/
CFB_Decryption::CFB_Decryption(BlockCipher* ciph,
const SymmetricKey& key,
const InitializationVector& iv,
u32bit fback_bits) :
BlockCipherMode(ciph, "CFB", ciph->BLOCK_SIZE, 1),
FEEDBACK_SIZE(fback_bits ? fback_bits / 8 : BLOCK_SIZE)
{
check_feedback(BLOCK_SIZE, FEEDBACK_SIZE, fback_bits, name());
set_key(key);
set_iv(iv);
}
/*
* Decrypt data in CFB mode
*/
void CFB_Decryption::write(const byte input[], u32bit length)
{
while(length)
{
u32bit xored = std::min(FEEDBACK_SIZE - position, length);
xor_buf(buffer + position, input, xored);
send(buffer + position, xored);
buffer.copy(position, input, xored);
input += xored;
length -= xored;
position += xored;
if(position == FEEDBACK_SIZE)
feedback();
}
}
/*
* Do the feedback
*/
void CFB_Decryption::feedback()
{
for(u32bit j = 0; j != BLOCK_SIZE - FEEDBACK_SIZE; ++j)
state[j] = state[j + FEEDBACK_SIZE];
state.copy(BLOCK_SIZE - FEEDBACK_SIZE, buffer, FEEDBACK_SIZE);
cipher->encrypt(state, buffer);
position = 0;
}
}
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