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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/cmac.h>
#include <botan/xor_buf.h>
#include <botan/parsing.h>
#include <algorithm>
namespace Botan {
namespace {
/*
* EAX MAC-based PRF
*/
SecureVector<byte> eax_prf(byte tag, u32bit BLOCK_SIZE,
MessageAuthenticationCode* mac,
const byte in[], u32bit length)
{
for(u32bit j = 0; j != BLOCK_SIZE - 1; ++j)
mac->update(0);
mac->update(tag);
mac->update(in, length);
return mac->final();
}
}
/*
* EAX_Base Constructor
*/
EAX_Base::EAX_Base(BlockCipher* ciph,
u32bit tag_size) :
TAG_SIZE(tag_size ? tag_size / 8 : ciph->BLOCK_SIZE),
BLOCK_SIZE(ciph->BLOCK_SIZE)
{
cipher = ciph;
mac = new CMAC(cipher->clone());
if(tag_size % 8 != 0 || TAG_SIZE == 0 || TAG_SIZE > mac->OUTPUT_LENGTH)
throw Invalid_Argument(name() + ": Bad tag size " + to_string(tag_size));
state.resize(BLOCK_SIZE);
buffer.resize(BLOCK_SIZE);
position = 0;
}
/*
* Check if a keylength is valid for EAX
*/
bool EAX_Base::valid_keylength(u32bit n) const
{
if(!cipher->valid_keylength(n))
return false;
if(!mac->valid_keylength(n))
return false;
return true;
}
/*
* Set the EAX key
*/
void EAX_Base::set_key(const SymmetricKey& key)
{
cipher->set_key(key);
mac->set_key(key);
header_mac = eax_prf(1, BLOCK_SIZE, mac, 0, 0);
}
/*
* Do setup at the start of each message
*/
void EAX_Base::start_msg()
{
for(u32bit j = 0; j != BLOCK_SIZE - 1; ++j)
mac->update(0);
mac->update(2);
}
/*
* Set the EAX nonce
*/
void EAX_Base::set_iv(const InitializationVector& iv)
{
nonce_mac = eax_prf(0, BLOCK_SIZE, mac, iv.begin(), iv.length());
state = nonce_mac;
cipher->encrypt(state, buffer);
}
/*
* Set the EAX header
*/
void EAX_Base::set_header(const byte header[], u32bit length)
{
header_mac = eax_prf(1, BLOCK_SIZE, mac, header, length);
}
/*
* Return the name of this cipher mode
*/
std::string EAX_Base::name() const
{
return (cipher->name() + "/EAX");
}
/*
* Increment the counter and update the buffer
*/
void EAX_Base::increment_counter()
{
for(s32bit j = BLOCK_SIZE - 1; j >= 0; --j)
if(++state[j])
break;
cipher->encrypt(state, buffer);
position = 0;
}
/*
* Encrypt in EAX mode
*/
void EAX_Encryption::write(const byte input[], u32bit length)
{
u32bit copied = std::min(BLOCK_SIZE - position, length);
xor_buf(buffer + position, input, copied);
send(buffer + position, copied);
mac->update(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);
mac->update(buffer, BLOCK_SIZE);
input += BLOCK_SIZE;
length -= BLOCK_SIZE;
increment_counter();
}
xor_buf(buffer + position, input, length);
send(buffer + position, length);
mac->update(buffer + position, length);
position += length;
}
/*
* Finish encrypting in EAX mode
*/
void EAX_Encryption::end_msg()
{
SecureVector<byte> data_mac = mac->final();
xor_buf(data_mac, nonce_mac, data_mac.size());
xor_buf(data_mac, header_mac, data_mac.size());
send(data_mac, TAG_SIZE);
state.clear();
buffer.clear();
position = 0;
}
}
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