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/*
* EAX Mode Encryption
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/eax.h>
#include <botan/xor_buf.h>
#include <botan/parsing.h>
#include <algorithm>
namespace Botan {
/*
* EAX_Decryption Constructor
*/
EAX_Decryption::EAX_Decryption(BlockCipher* ciph,
u32bit tag_size) :
EAX_Base(ciph, tag_size)
{
queue.resize(2*TAG_SIZE + DEFAULT_BUFFERSIZE);
queue_start = queue_end = 0;
}
/*
* EAX_Decryption Constructor
*/
EAX_Decryption::EAX_Decryption(BlockCipher* ciph,
const SymmetricKey& key,
const InitializationVector& iv,
u32bit tag_size) :
EAX_Base(ciph, tag_size)
{
set_key(key);
set_iv(iv);
queue.resize(2*TAG_SIZE + DEFAULT_BUFFERSIZE);
queue_start = queue_end = 0;
}
/*
* Decrypt in EAX mode
*/
void EAX_Decryption::write(const byte input[], u32bit length)
{
while(length)
{
const u32bit copied = std::min(length, queue.size() - queue_end);
queue.copy(queue_end, input, copied);
input += copied;
length -= copied;
queue_end += copied;
SecureVector<byte> block_buf(cipher->BLOCK_SIZE);
while((queue_end - queue_start) > TAG_SIZE)
{
u32bit removed = (queue_end - queue_start) - TAG_SIZE;
do_write(queue + queue_start, removed);
queue_start += removed;
}
if(queue_start + TAG_SIZE == queue_end &&
queue_start >= queue.size() / 2)
{
SecureVector<byte> queue_data(TAG_SIZE);
queue_data.copy(queue + queue_start, TAG_SIZE);
queue.copy(queue_data, TAG_SIZE);
queue_start = 0;
queue_end = TAG_SIZE;
}
}
}
/*
* Decrypt in EAX mode
*/
void EAX_Decryption::do_write(const byte input[], u32bit length)
{
mac->update(input, length);
u32bit copied = std::min(BLOCK_SIZE - position, length);
xor_buf(buffer + position, input, copied);
send(buffer + position, copied);
input += copied;
length -= copied;
position += copied;
if(position == BLOCK_SIZE)
increment_counter();
while(length >= BLOCK_SIZE)
{
xor_buf(buffer, input, BLOCK_SIZE);
send(buffer, BLOCK_SIZE);
input += BLOCK_SIZE;
length -= BLOCK_SIZE;
increment_counter();
}
xor_buf(buffer + position, input, length);
send(buffer + position, length);
position += length;
}
/*
* Finish decrypting in EAX mode
*/
void EAX_Decryption::end_msg()
{
if((queue_end - queue_start) != TAG_SIZE)
throw Integrity_Failure(name() + ": Message authentication failure");
SecureVector<byte> data_mac = mac->final();
for(u32bit j = 0; j != TAG_SIZE; ++j)
if(queue[queue_start+j] != (data_mac[j] ^ nonce_mac[j] ^ header_mac[j]))
throw Integrity_Failure(name() + ": Message authentication failure");
state.clear();
buffer.clear();
position = 0;
queue_start = queue_end = 0;
}
}
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