cmac.cpp

// 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 &params)
{
        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