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/*************************************************
* CMAC Source File *
* (C) 1999-2007 The Botan Project *
*************************************************/
#include <botan/cmac.h>
#include <botan/lookup.h>
#include <botan/bit_ops.h>
namespace Botan {
namespace {
/*************************************************
* Perform CMAC's multiplication in GF(2^n) *
*************************************************/
SecureVector<byte> poly_double(const MemoryRegion<byte>& in, byte polynomial)
{
const bool do_xor = (in[0] & 0x80) ? true : false;
SecureVector<byte> out = in;
byte carry = 0;
for(u32bit j = out.size(); j != 0; --j)
{
byte temp = out[j-1];
out[j-1] = (temp << 1) | carry;
carry = (temp >> 7);
}
if(do_xor)
out[out.size()-1] ^= polynomial;
return out;
}
}
/*************************************************
* Update an CMAC Calculation *
*************************************************/
void CMAC::add_data(const byte input[], u32bit length)
{
buffer.copy(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;
}
buffer.copy(input, length);
position = 0;
}
position += length;
}
/*************************************************
* Finalize an CMAC Calculation *
*************************************************/
void CMAC::final_result(byte mac[])
{
if(position == OUTPUT_LENGTH)
xor_buf(buffer, B, OUTPUT_LENGTH);
else
{
buffer[position] = 0x80;
for(u32bit j = position+1; j != OUTPUT_LENGTH; ++j)
buffer[j] = 0;
xor_buf(buffer, P, OUTPUT_LENGTH);
}
xor_buf(state, buffer, OUTPUT_LENGTH);
e->encrypt(state);
for(u32bit j = 0; j != OUTPUT_LENGTH; ++j)
mac[j] = state[j];
state.clear();
buffer.clear();
position = 0;
}
/*************************************************
* CMAC Key Schedule *
*************************************************/
void CMAC::key(const byte key[], u32bit 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() throw()
{
e->clear();
state.clear();
buffer.clear();
B.clear();
P.clear();
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->name());
}
/*************************************************
* CMAC Constructor *
*************************************************/
CMAC::CMAC(const std::string& bc_name) :
MessageAuthenticationCode(block_size_of(bc_name),
min_keylength_of(bc_name),
max_keylength_of(bc_name),
keylength_multiple_of(bc_name))
{
e = get_block_cipher(bc_name);
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.create(OUTPUT_LENGTH);
buffer.create(OUTPUT_LENGTH);
B.create(OUTPUT_LENGTH);
P.create(OUTPUT_LENGTH);
position = 0;
}
}
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