cmac.cpp
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// cmac.cpp - written and placed in the public domain by Wei Dai
#include "pch.h"
#ifndef CRYPTOPP_IMPORTS
#include "cmac.h"
NAMESPACE_BEGIN(CryptoPP)
static void MulU(byte *k, unsigned int length)
{
byte carry = 0;
for (int i=length-1; i>=1; i-=2)
{
byte carry2 = k[i] >> 7;
k[i] += k[i] + carry;
carry = k[i-1] >> 7;
k[i-1] += k[i-1] + carry2;
}
if (carry)
{
switch (length)
{
case 8:
k[7] ^= 0x1b;
break;
case 16:
k[15] ^= 0x87;
break;
case 32:
k[30] ^= 4;
k[31] ^= 0x23;
break;
default:
throw InvalidArgument("CMAC: " + IntToString(length) + " is not a supported cipher block size");
}
}
}
void CMAC_Base::UncheckedSetKey(const byte *key, unsigned int length, const NameValuePairs ¶ms)
{
BlockCipher &cipher = AccessCipher();
unsigned int blockSize = cipher.BlockSize();
cipher.SetKey(key, length, params);
m_reg.CleanNew(3*blockSize);
m_counter = 0;
cipher.ProcessBlock(m_reg, m_reg+blockSize);
MulU(m_reg+blockSize, blockSize);
memcpy(m_reg+2*blockSize, m_reg+blockSize, blockSize);
MulU(m_reg+2*blockSize, blockSize);
}
void CMAC_Base::Update(const byte *input, size_t length)
{
if (!length)
return;
BlockCipher &cipher = AccessCipher();
unsigned int blockSize = cipher.BlockSize();
if (m_counter > 0)
{
unsigned int len = UnsignedMin(blockSize - m_counter, length);
xorbuf(m_reg+m_counter, input, len);
length -= len;
input += len;
m_counter += len;
if (m_counter == blockSize && length > 0)
{
cipher.ProcessBlock(m_reg);
m_counter = 0;
}
}
if (length > blockSize)
{
assert(m_counter == 0);
size_t leftOver = 1 + cipher.AdvancedProcessBlocks(m_reg, input, m_reg, length-1, BlockTransformation::BT_DontIncrementInOutPointers|BlockTransformation::BT_XorInput);
input += (length - leftOver);
length = leftOver;
}
if (length > 0)
{
assert(m_counter + length <= blockSize);
xorbuf(m_reg+m_counter, input, length);
m_counter += (unsigned int)length;
}
assert(m_counter > 0);
}
void CMAC_Base::TruncatedFinal(byte *mac, size_t size)
{
ThrowIfInvalidTruncatedSize(size);
BlockCipher &cipher = AccessCipher();
unsigned int blockSize = cipher.BlockSize();
if (m_counter < blockSize)
{
m_reg[m_counter] ^= 0x80;
cipher.AdvancedProcessBlocks(m_reg, m_reg+2*blockSize, m_reg, blockSize, BlockTransformation::BT_DontIncrementInOutPointers|BlockTransformation::BT_XorInput);
}
else
cipher.AdvancedProcessBlocks(m_reg, m_reg+blockSize, m_reg, blockSize, BlockTransformation::BT_DontIncrementInOutPointers|BlockTransformation::BT_XorInput);
memcpy(mac, m_reg, size);
m_counter = 0;
memset(m_reg, 0, blockSize);
}
NAMESPACE_END
#endif