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/*
* CMAC
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/cmac.h>
#include <botan/internal/xor_buf.h>
namespace Botan {
/*
* Perform CMAC's multiplication in GF(2^n)
*/
secure_vector<byte> CMAC::poly_double(const secure_vector<byte>& in,
byte polynomial)
{
const byte poly_xor = (in[0] & 0x80) ? polynomial : 0;
secure_vector<byte> out = in;
byte carry = 0;
for(size_t i = out.size(); i != 0; --i)
{
byte temp = out[i-1];
out[i-1] = (temp << 1) | carry;
carry = (temp >> 7);
}
out[out.size()-1] ^= poly_xor;
return out;
}
/*
* Update an CMAC Calculation
*/
void CMAC::add_data(const byte input[], size_t length)
{
buffer_insert(buffer, position, input, length);
if(position + length > output_length())
{
xor_buf(state, buffer, output_length());
e->encrypt(state);
input += (output_length() - position);
length -= (output_length() - position);
while(length > output_length())
{
xor_buf(state, input, output_length());
e->encrypt(state);
input += output_length();
length -= output_length();
}
copy_mem(&buffer[0], input, length);
position = 0;
}
position += length;
}
/*
* Finalize an CMAC Calculation
*/
void CMAC::final_result(byte mac[])
{
xor_buf(state, buffer, position);
if(position == output_length())
{
xor_buf(state, B, output_length());
}
else
{
state[position] ^= 0x80;
xor_buf(state, P, output_length());
}
e->encrypt(state);
for(size_t i = 0; i != output_length(); ++i)
mac[i] = state[i];
zeroise(state);
zeroise(buffer);
position = 0;
}
/*
* CMAC Key Schedule
*/
void CMAC::key_schedule(const byte key[], size_t length)
{
clear();
e->set_key(key, length);
e->encrypt(B);
B = poly_double(B, polynomial);
P = poly_double(B, polynomial);
}
/*
* Clear memory of sensitive data
*/
void CMAC::clear()
{
e->clear();
zeroise(state);
zeroise(buffer);
zeroise(B);
zeroise(P);
position = 0;
}
/*
* Return the name of this type
*/
std::string CMAC::name() const
{
return "CMAC(" + e->name() + ")";
}
/*
* Return a clone of this object
*/
MessageAuthenticationCode* CMAC::clone() const
{
return new CMAC(e->clone());
}
/*
* CMAC Constructor
*/
CMAC::CMAC(BlockCipher* e_in) : e(e_in)
{
if(e->block_size() == 16)
polynomial = 0x87;
else if(e->block_size() == 8)
polynomial = 0x1B;
else
throw Invalid_Argument("CMAC cannot use the cipher " + e->name());
state.resize(output_length());
buffer.resize(output_length());
B.resize(output_length());
P.resize(output_length());
position = 0;
}
/*
* CMAC Destructor
*/
CMAC::~CMAC()
{
delete e;
}
}
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