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/*
* CMAC
* (C) 1999-2007,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/cmac.h>
namespace Botan {
CMAC* CMAC::make(const Spec& spec)
{
if(spec.arg_count() == 1)
{
if(auto bc = BlockCipher::create(spec.arg(0)))
return new CMAC(bc.release());
}
return nullptr;
}
/*
* Perform CMAC's multiplication in GF(2^n)
*/
secure_vector<byte> CMAC::poly_double(const secure_vector<byte>& in)
{
const bool top_carry = static_cast<bool>((in[0] & 0x80) != 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);
}
if(top_carry)
{
switch(in.size())
{
case 8:
out[out.size()-1] ^= 0x1B;
break;
case 16:
out[out.size()-1] ^= 0x87;
break;
case 32:
out[out.size()-2] ^= 0x4;
out[out.size()-1] ^= 0x25;
break;
case 64:
out[out.size()-2] ^= 0x1;
out[out.size()-1] ^= 0x25;
break;
default:
throw std::runtime_error("Unsupported CMAC size " + std::to_string(in.size()));
}
}
return out;
}
/*
* Update an CMAC Calculation
*/
void CMAC::add_data(const byte input[], size_t length)
{
buffer_insert(m_buffer, m_position, input, length);
if(m_position + length > output_length())
{
xor_buf(m_state, m_buffer, output_length());
m_cipher->encrypt(m_state);
input += (output_length() - m_position);
length -= (output_length() - m_position);
while(length > output_length())
{
xor_buf(m_state, input, output_length());
m_cipher->encrypt(m_state);
input += output_length();
length -= output_length();
}
copy_mem(m_buffer.data(), input, length);
m_position = 0;
}
m_position += length;
}
/*
* Finalize an CMAC Calculation
*/
void CMAC::final_result(byte mac[])
{
xor_buf(m_state, m_buffer, m_position);
if(m_position == output_length())
{
xor_buf(m_state, m_B, output_length());
}
else
{
m_state[m_position] ^= 0x80;
xor_buf(m_state, m_P, output_length());
}
m_cipher->encrypt(m_state);
for(size_t i = 0; i != output_length(); ++i)
mac[i] = m_state[i];
zeroise(m_state);
zeroise(m_buffer);
m_position = 0;
}
/*
* CMAC Key Schedule
*/
void CMAC::key_schedule(const byte key[], size_t length)
{
clear();
m_cipher->set_key(key, length);
m_cipher->encrypt(m_B);
m_B = poly_double(m_B);
m_P = poly_double(m_B);
}
/*
* Clear memory of sensitive data
*/
void CMAC::clear()
{
m_cipher->clear();
zeroise(m_state);
zeroise(m_buffer);
zeroise(m_B);
zeroise(m_P);
m_position = 0;
}
/*
* Return the name of this type
*/
std::string CMAC::name() const
{
return "CMAC(" + m_cipher->name() + ")";
}
/*
* Return a clone of this object
*/
MessageAuthenticationCode* CMAC::clone() const
{
return new CMAC(m_cipher->clone());
}
/*
* CMAC Constructor
*/
CMAC::CMAC(BlockCipher* cipher) : m_cipher(cipher)
{
if(m_cipher->block_size() != 8 && m_cipher->block_size() != 16 &&
m_cipher->block_size() != 32 && m_cipher->block_size() != 64)
{
throw Invalid_Argument("CMAC cannot use the " +
std::to_string(m_cipher->block_size() * 8) +
" bit cipher " + m_cipher->name());
}
m_state.resize(output_length());
m_buffer.resize(output_length());
m_B.resize(output_length());
m_P.resize(output_length());
m_position = 0;
}
}
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