AES.cpp

/* AES - Advanced Encryption Standard

  source version 1.0, June, 2005

  Copyright (C) 2000-2005 Chris Lomont

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the author be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Chris Lomont
  chris@lomont.org

  The AES Standard is maintained by NIST
  http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf

  This legalese is patterned after the zlib compression library
*/

// code to implement Advanced Encryption Standard - Rijndael
// speed optimized version
#include "AES.h"
#include <algorithm>
#include <stdio.h>
#include <string.h>

// todo - make faster 128 blocksize version with 128 blocksize hardcoded as necessary

// internally data is stored in the state in order
//   0  1  2  3
//   4  5  6  7
//   8  8 10 11
//   ...
// up to Nb of these
// NOTE: thus rows and columns are interchanged from the paper

using namespace std;

namespace { // anonymous namespace for local linkage

// tables for inverses, byte sub
unsigned char gf2_8_inv[256];
unsigned char byte_sub[256];
unsigned char inv_byte_sub[256];

// this table needs Nb*(Nr+1)/Nk entries - up to 8*(15)/4 = 60
// todo - remove table, note cycles every 17(?) elements
unsigned long Rcon[60];

// long tables for encryption stuff
unsigned long T0[256];
unsigned long T1[256];
unsigned long T2[256];
unsigned long T3[256];

// long tables for decryption stuff
unsigned long I0[256];
unsigned long I1[256];
unsigned long I2[256];
unsigned long I3[256];

// huge tables - todo - ifdef out
unsigned long T4[256];
unsigned long T5[256];
unsigned long T6[256];
unsigned long T7[256];
unsigned long I4[256];
unsigned long I5[256];
unsigned long I6[256];
unsigned long I7[256];

// have the tables been initialized?
bool tablesInitialized = false;

// define to mult a byte by x mod the proper poly
// todo - move magic numbers out?
#define xmult(a) ((a)<<1) ^ (((a)&128) ? 0x01B : 0)

// make 4 bytes (LSB first) into a 4 byte vector
#define VEC4(a,b,c,d) (((unsigned long)(a)) | (((unsigned long)(b))<<8) | (((unsigned long)(c))<<16) | (((unsigned long)(d))<<24))

// get byte 0 to 3 from word a
#define GetByte(a,n) ((unsigned char)((a) >> (n<<3)))

/* rotates x one bit to the left */
#define ROTL(x) (((x)>>7)|((x)<<1))

/* Rotates 32-bit word left by 1, 2 or 3 byte  */
#define ROTL8(x) (((x)<<8)|((x)>>24))
#define ROTL16(x) (((x)<<16)|((x)>>16))
#define ROTL24(x) (((x)<<24)|((x)>>8))

//	bytes (a,b,c,d) -> (b,c,d,a) so low becomes high
#define RotByte(a) ROTL24(a)

#define RotByteL(a) ROTL8(a)

// mult 2 elements using gf2_8_poly as a reduction
inline unsigned char GF2_8_mult(unsigned char a, unsigned char b)
	{ // todo - make 4x4 table for nibbles, use lookup
	unsigned char result = 0;

	// should give 0x57 . 0x13 = 0xFE with poly 0x11B
	//

	int count = 8;
	while (count--)
		{
		if (b&1)
			result ^= a;
		if (a&128)
			{
			a <<= 1;
			a ^= (0x1B);
			}
		else
			a <<= 1;
		b >>= 1;
		}
	return result;
	} // GF2_8_mult

bool CheckLargeTables(bool create)
	{
	unsigned int i;
	unsigned char a1,a2,a3,b1,b2,b3,b4,b5;
	for (i = 0; i < 256; i++)
		{
		a1 = byte_sub[i];
		a2 = xmult(a1);
		a3 = a2^a1;

		b5 = inv_byte_sub[i];
		b1 = GF2_8_mult(0x0E,b5);
		b2 = GF2_8_mult(0x09,b5);
		b3 = GF2_8_mult(0x0D,b5);
		b4 = GF2_8_mult(0x0B,b5);

		if (create == true)
			{
			T0[i] = VEC4(a2,a1,a1,a3);
			T1[i] = RotByteL(T0[i]);
			T2[i] = RotByteL(T1[i]);
			T3[i] = RotByteL(T2[i]);

			T4[i] = VEC4(a1,0,0,0); // identity
			T5[i] = RotByteL(T4[i]);
			T6[i] = RotByteL(T5[i]);
			T7[i] = RotByteL(T6[i]);

			I0[i] = VEC4(b1,b2,b3,b4);
			I1[i] = RotByteL(I0[i]);
			I2[i] = RotByteL(I1[i]);
			I3[i] = RotByteL(I2[i]);

			I4[i] = VEC4(b5,0,0,0); // identity
			I5[i] = RotByteL(I4[i]);
			I6[i] = RotByteL(I5[i]);
			I7[i] = RotByteL(I6[i]);
			}
		else
			{
			if (T0[i] != VEC4(a2,a1,a1,a3))
				return false;
			if (T1[i] != RotByteL(T0[i]))
				return false;
			if (T2[i] != RotByteL(T1[i]))
				return false;
			if (T3[i] != RotByteL(T2[i]))
				return false;
			if (T4[i] != VEC4(a1,0,0,0))
				return false;
			if (T5[i] != RotByteL(T4[i]))
				return false;
			if (T6[i] != RotByteL(T5[i]))
				return false;
			if (T7[i] != RotByteL(T6[i]))
				return false;
			if (I0[i] != VEC4(b1,b2,b3,b4))
				return false;
			if (I1[i] != RotByte(I0[i]))
				return false;
			if (I2[i] != RotByte(I1[i]))
				return false;
			if (I3[i] != RotByte(I2[i]))
				return false;
			if (I4[i] != VEC4(b5,0,0,0))
				return false;
			if (I5[i] != RotByteL(I4[i]))
				return false;
			if (I6[i] != RotByteL(I5[i]))
				return false;
			if (I7[i] != RotByteL(I6[i]))
				return false;
			}
		}
	return true;
	} // CheckLargeTables

// some functions to create/verify table integrity
bool CheckInverses(bool create)
	{
	unsigned int a,b; // need int here to prevent wraps in loop
	if (create == true)
		gf2_8_inv[0] = 0;
	else if (gf2_8_inv[0] != 0)
		return false;
	for (a = 1; a <= 255; a++)
		{
		b = 1;
		while (GF2_8_mult(a,b) != 1)
			b++;

		if (create == true)
			gf2_8_inv[a] = b;
		else if (gf2_8_inv[a] != b)
			return false;
		}
	return true;
	} // CheckInverses

unsigned char BitSum(unsigned char byte)
	{ // return the sum of bits mod 2
	byte = (byte>>4)^(byte&15);
	byte = (byte>>2)^(byte&3);
	return (byte>>1)^(byte&1);
	} // BitSum

bool CheckByteSub(bool create)
	{
	if (CheckInverses(create) == false)
		return false; // we cannot do this without inverses

	unsigned int x,y; // need ints here to prevent wrap in loop
	for (x = 0; x <= 255; x++)
		{
		y = gf2_8_inv[x]; // inverse to start with

		// affine transform
		y = BitSum(y&0xF1) | (BitSum(y&0xE3)<<1) | (BitSum(y&0xC7)<<2) | (BitSum(y&0x8F)<<3) |
			(BitSum(y&0x1F)<<4) | (BitSum(y&0x3E)<<5) | (BitSum(y&0x7C)<<6) | (BitSum(y&0xF8)<<7);
		y = y ^ 0x63;
		if (create == true)
			byte_sub[x] = y;
		else if (byte_sub[x] != y)
			return false;
		}
	return true;
	} // CheckByteSub

bool CheckInvByteSub(bool create)
	{
	if (CheckInverses(create) == false)
		return false; // we cannot do this without inverses
	if (CheckByteSub(create) == false)
		return false; // we cannot do this without byte_sub

	unsigned int x,y; // need ints here to prevent wrap in loop
	for (x = 0; x <= 255; x++)
		{
		// we brute force it...
		y = 0;
		while (byte_sub[y] != x)
			y++;
		if (create == true)
			inv_byte_sub[x] = y;
		else if (inv_byte_sub[x] != y)
			return false;
		}
	return true;
	} // CheckInvByteSub

bool CheckRcon(bool create)
	{
	unsigned char Ri = 1; // start here

	if (create == true)
		Rcon[0] = 0;
	else if (Rcon[0] != 0)
		return false; // todo - this is unused still check?
	for (unsigned int i = 1; i < sizeof(Rcon)/sizeof(Rcon[0])-1; i++)
		{
		if (create == true)
			Rcon[i] = Ri;
		else if (Rcon[i] != Ri)
			return false;
		Ri = GF2_8_mult(Ri,0x02); // multiply by x - todo replace with xmult
		}
	return true;
	} // CheckRCon

// key adding for 4,6,8 column cases
#define AddRoundKey4(dest,src)	\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;

#define AddRoundKey6(dest,src)	\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;

#define AddRoundKey8(dest,src)	\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;\
	*dest++ = *r_ptr++ ^ *src++;

// this define computes one of the round vectors
#define compute_one(dest,src2,j,C1,C2,C3,Nb)	*(dest+j) = \
	T0[GetByte(src2[j],0)]^T1[GetByte(src2[((j+C1+Nb)%Nb)],1)]^ \
	T2[GetByte(src2[((j+C2+Nb)%Nb)],2)]^T3[GetByte(src2[((j+C3+Nb)%Nb)],3)] \
	^*r_ptr++

// single table version, slower
#define compute_one_small(dest,src2,j,C1,C2,C3,Nb)	*(dest+j) = *r_ptr++^\
	T0[GetByte(src2[j],0)]^\
	RotByteL(T0[GetByte(src2[((j+C1+Nb)%Nb)],1)]^\
	RotByteL(T0[GetByte(src2[((j+C2+Nb)%Nb)],2)]^\
	RotByteL(T0[GetByte(src2[((j+C3+Nb)%Nb)],3)])))

#define Round4(d,s)	\
		compute_one(d,s,0,1,2,3,4); \
		compute_one(d,s,1,1,2,3,4);	\
		compute_one(d,s,2,1,2,3,4);	\
		compute_one(d,s,3,1,2,3,4);

#define Round6(d,s) \
		compute_one(d,s,0,1,2,3,6); \
		compute_one(d,s,1,1,2,3,6); \
		compute_one(d,s,2,1,2,3,6); \
		compute_one(d,s,3,1,2,3,6); \
		compute_one(d,s,4,1,2,3,6); \
		compute_one(d,s,5,1,2,3,6);

#define Round8(d,s) \
		compute_one(d,s,0,1,3,4,8); \
		compute_one(d,s,1,1,3,4,8); \
		compute_one(d,s,2,1,3,4,8); \
		compute_one(d,s,3,1,3,4,8); \
		compute_one(d,s,4,1,3,4,8); \
		compute_one(d,s,5,1,3,4,8); \
		compute_one(d,s,6,1,3,4,8); \
		compute_one(d,s,7,1,3,4,8);

#define compute_one_inv(dest,src2,j,C1,C2,C3,Nb)	*(dest+j) = \
	I0[GetByte(src2[j],0)]^I1[GetByte(src2[((j-C1+Nb)%Nb)],1)]^ \
	I2[GetByte(src2[((j-C2+Nb)%Nb)],2)]^I3[GetByte(src2[((j-C3+Nb)%Nb)],3)] \
	^*r_ptr++

#define InvRound4(d,s)	\
		compute_one_inv(d,s,0,1,2,3,4); \
		compute_one_inv(d,s,1,1,2,3,4);	\
		compute_one_inv(d,s,2,1,2,3,4);	\
		compute_one_inv(d,s,3,1,2,3,4);

#define InvRound6(d,s)	\
		compute_one_inv(d,s,0,1,2,3,6); \
		compute_one_inv(d,s,1,1,2,3,6);	\
		compute_one_inv(d,s,2,1,2,3,6);	\
		compute_one_inv(d,s,3,1,2,3,6);	\
		compute_one_inv(d,s,4,1,2,3,6);	\
		compute_one_inv(d,s,5,1,2,3,6);

#define InvRound8(d,s)	\
		compute_one_inv(d,s,0,1,3,4,8); \
		compute_one_inv(d,s,1,1,3,4,8);	\
		compute_one_inv(d,s,2,1,3,4,8);	\
		compute_one_inv(d,s,3,1,3,4,8);	\
		compute_one_inv(d,s,4,1,3,4,8);	\
		compute_one_inv(d,s,5,1,3,4,8);	\
		compute_one_inv(d,s,6,1,3,4,8);	\
		compute_one_inv(d,s,7,1,3,4,8);

// this define computes one of the final round vectors
#define compute_one_final1(dest,src,j,C1,C2,C3,Nb)  *dest++ = \
	(T3[GetByte(src[j],0)]&0xFF)^\
	(T3[GetByte(src[((j+C1+Nb)%Nb)],1)]&0xFF00)^ \
	(T1[GetByte(src[((j+C2+Nb)%Nb)],2)]&0xFF0000)^ \
	(T1[GetByte(src[((j+C3+Nb)%Nb)],3)]&0xFF000000)^*r_ptr++

// for another 4K tables, we save 3 clock cycles - sick
#define compute_one_final(dest,src,j,C1,C2,C3,Nb)  *dest++ = \
	(T4[GetByte(src[j],0)])^\
	(T5[GetByte(src[((j+C1+Nb)%Nb)],1)])^ \
	(T6[GetByte(src[((j+C2+Nb)%Nb)],2)])^ \
	(T7[GetByte(src[((j+C3+Nb)%Nb)],3)])^*r_ptr++

// final round defines - this one is for case for 4 columns
#define FinalRound4(d,s) compute_one_final(d,s,0,1,2,3,4); \
						compute_one_final(d,s,1,1,2,3,4); \
						compute_one_final(d,s,2,1,2,3,4); \
						compute_one_final(d,s,3,1,2,3,4);

#define FinalRound6(d,s) compute_one_final(d,s,0,1,2,3,6); \
						compute_one_final(d,s,1,1,2,3,6); \
						compute_one_final(d,s,2,1,2,3,6); \
						compute_one_final(d,s,3,1,2,3,6); \
						compute_one_final(d,s,4,1,2,3,6); \
						compute_one_final(d,s,5,1,2,3,6);

#define FinalRound8(d,s) compute_one_final(d,s,0,1,3,4,8); \
						compute_one_final(d,s,1,1,3,4,8); \
						compute_one_final(d,s,2,1,3,4,8); \
						compute_one_final(d,s,3,1,3,4,8); \
						compute_one_final(d,s,4,1,3,4,8); \
						compute_one_final(d,s,5,1,3,4,8); \
						compute_one_final(d,s,6,1,3,4,8); \
						compute_one_final(d,s,7,1,3,4,8);

// inverse cipher stuff
#define compute_one_final_inv(dest,src,j,C1,C2,C3,Nb)  *dest++ = \
	(I4[GetByte(src[j],0)])^\
	(I5[GetByte(src[((j-C1+Nb)%Nb)],1)])^ \
	(I6[GetByte(src[((j-C2+Nb)%Nb)],2)])^ \
	(I7[GetByte(src[((j-C3+Nb)%Nb)],3)])^*r_ptr++

// final round defines - this one is for case for 4 columns
#define InvFinalRound4(d,s) compute_one_final_inv(d,s,0,1,2,3,4); \
						compute_one_final_inv(d,s,1,1,2,3,4); \
						compute_one_final_inv(d,s,2,1,2,3,4); \
						compute_one_final_inv(d,s,3,1,2,3,4);

#define InvFinalRound6(d,s) compute_one_final_inv(d,s,0,1,2,3,6); \
						compute_one_final_inv(d,s,1,1,2,3,6); \
						compute_one_final_inv(d,s,2,1,2,3,6); \
						compute_one_final_inv(d,s,3,1,2,3,6); \
						compute_one_final_inv(d,s,4,1,2,3,6); \
						compute_one_final_inv(d,s,5,1,2,3,6);

#define InvFinalRound8(d,s) compute_one_final_inv(d,s,0,1,3,4,8); \
						compute_one_final_inv(d,s,1,1,3,4,8); \
						compute_one_final_inv(d,s,2,1,3,4,8); \
						compute_one_final_inv(d,s,3,1,3,4,8); \
						compute_one_final_inv(d,s,4,1,3,4,8); \
						compute_one_final_inv(d,s,5,1,3,4,8); \
						compute_one_final_inv(d,s,6,1,3,4,8); \
						compute_one_final_inv(d,s,7,1,3,4,8);

unsigned long SubByte(unsigned long data)
	{ // does the SBox on this 4 byte data
	unsigned result = 0;
	result = byte_sub[data>>24];
	result <<= 8;
	result |= byte_sub[(data>>16)&255];
	result <<= 8;
	result |= byte_sub[(data>>8)&255];
	result <<= 8;
	result |= byte_sub[data&255];
	return result;
	} // SubByte

// return true iff tables are valid. create = true fills them in if not
bool CreateAESTables(bool create)
	{
	bool retval = true;
	if (CheckInverses(create) == false)
		retval = false;
	if (CheckByteSub(create) == false)
		retval = false;
	if (CheckInvByteSub(create) == false)
		retval = false;
	if (CheckRcon(create) == false)
		return false;
	if (CheckLargeTables(create) == false)
		return false;
	return retval;
	} // CreateAESTables

}// end of anonymous namespace

// Key expansion code - makes local copy
void AES::KeyExpansion(const unsigned char * key)
	{
	int i;
	unsigned long temp, * Wb = reinterpret_cast<unsigned long*>(W); // todo not portable - Endian problems
	if (Nk <= 6)
		{
		// todo - memcpy
		for (i = 0; i < 4*Nk; i++)
			W[i] = key[i];
		for (i = Nk; i < Nb*(Nr+1); i++)
			{
			temp = Wb[i-1];
			if ((i%Nk) == 0)
				temp = SubByte(RotByte(temp)) ^ Rcon[i/Nk];
			Wb[i] = Wb[i - Nk]^temp;
			}
		}
	else
		{
		// todo - memcpy
		for (i = 0; i < 4*Nk; i++)
			W[i] = key[i];
		for (i = Nk; i < Nb*(Nr+1); i++)
			{
			temp = Wb[i-1];
			if ((i%Nk) == 0)
				temp = SubByte(RotByte(temp)) ^ Rcon[i/Nk];
			else if ((i%Nk) == 4)
				temp = SubByte(temp);
			Wb[i] = Wb[i - Nk]^temp;
			}
		}
	} // KeyExpansion

void AES::SetParameters(int keylength, int blocklength)
	{
	Nk = Nr = Nb = 0; // default values

	if ((keylength != 128) && (keylength != 192) && (keylength != 256))
		return; // nothing - todo - throw error?
	if ((blocklength != 128) && (blocklength != 192) && (blocklength != 256))
		return; // nothing - todo - throw error?

	static int const parameters[] = {
//Nk*32 128     192     256
		10, 	12,  	14,  // Nb*32 = 128
		12, 	12,  	14,  // Nb*32 = 192
		14, 	14,  	14,  // Nb*32 = 256
		};

	// legal parameters, so fire it up
	Nk = keylength  /32;
	Nb = blocklength/32;
	Nr = parameters[((Nk-4)/2 + 3*(Nb-4)/2)];
	} // SetParameters

void AES::SetIV(const unsigned char * ucIV, unsigned int iIVsize)
	{
		memcpy(iv, ucIV, (iIVsize > 32 ? 32 : iIVsize));
	}

void AES::StartEncryption(const unsigned char * key)
	{
	memset(iv, 0xff, sizeof(iv));
	KeyExpansion(key);
	} // StartEncryption

void AES::EncryptBlock(const unsigned char * datain1, unsigned char * dataout1)
	{ // todo ? allow in place encryption
	  // todo - clean up - lots of repeated macros
	  // we only encrypt one block from now on

	unsigned long state[8*2]; // 2 buffers
	unsigned long * r_ptr = reinterpret_cast<unsigned long*>(W);
	unsigned long * dest  = state;
	unsigned long * src   = state;
	const unsigned long * datain = reinterpret_cast<const unsigned long*>(datain1);
	unsigned long * dataout = reinterpret_cast<unsigned long*>(dataout1);

	if (Nb == 4)
		{
		AddRoundKey4(dest,datain);

		if (Nr == 14)
			{
			Round4(dest,src);
			Round4(src,dest);
			Round4(dest,src);
			Round4(src,dest);
			}
		else if (Nr == 12)
			{
			Round4(dest,src);
			Round4(src,dest);
			}

		Round4(dest,src);
		Round4(src,dest);
		Round4(dest,src);
		Round4(src,dest);
		Round4(dest,src);
		Round4(src,dest);
		Round4(dest,src);
		Round4(src,dest);
		Round4(dest,src);

		FinalRound4(dataout,dest);
		}
	else if (Nb == 6)
		{
		AddRoundKey6(dest,datain);

		if (Nr == 14)
			{
			Round6(dest,src);
			Round6(src,dest);
			}

		Round6(dest,src);
		Round6(src,dest);
		Round6(dest,src);
		Round6(src,dest);
		Round6(dest,src);
		Round6(src,dest);
		Round6(dest,src);
		Round6(src,dest);
		Round6(dest,src);
		Round6(src,dest);
		Round6(dest,src);

		FinalRound6(dataout,dest);
		}
	else // Nb == 8
		{
		AddRoundKey8(dest,datain);

		Round8(dest,src);
		Round8(src,dest);
		Round8(dest,src);
		Round8(src,dest);
		Round8(dest,src);
		Round8(src,dest);
		Round8(dest,src);
		Round8(src,dest);
		Round8(dest,src);
		Round8(src,dest);
		Round8(dest,src);
		Round8(src,dest);
		Round8(dest,src);

		FinalRound8(dataout,dest);
		} // end switch on Nb

	} // Encrypt

// call this to encrypt any size block
void AES::Encrypt(const unsigned char * datain, unsigned char * dataout, unsigned long numBlocks, BlockMode mode)
	{
	if (0 == numBlocks)
		return;
	unsigned int blocksize = Nb*4;
	switch (mode)
		{
		case ECB :
			while (numBlocks)
				{
				EncryptBlock(datain,dataout);
				datain   += blocksize;
				dataout  += blocksize;
				--numBlocks;
				}
			break;
		case CBC :
			{
			unsigned char buffer[32]; // max blocksize
			memcpy(buffer,iv,blocksize); // clear out - todo - allow setting the Initialization Vector - needed for security
			while (numBlocks)
				{
				for (unsigned int pos = 0; pos < blocksize; ++pos)
					buffer[pos] ^= *datain++;
				EncryptBlock(buffer,dataout);
				memcpy(buffer,dataout,blocksize);
				dataout  += blocksize;
				--numBlocks;
				}
			}
			break;
		default :
			break;
		}
	} // Encrypt

void AES::StartDecryption(const unsigned char * key)
	{
	memset(iv, 0xff, sizeof(iv));
	KeyExpansion(key);

	unsigned char a0,a1,a2,a3,b0,b1,b2,b3, * W_ptr = W;

	for (int col = Nb; col < (Nr)*Nb; col++) // do all but first and last round
		{
		a0 = W_ptr[4*col+0];
		a1 = W_ptr[4*col+1];
		a2 = W_ptr[4*col+2];
		a3 = W_ptr[4*col+3];

		b0 = GF2_8_mult(0x0E,a0)^GF2_8_mult(0x0B,a1)^
		     GF2_8_mult(0x0D,a2)^GF2_8_mult(0x09,a3);
		b1 = GF2_8_mult(0x09,a0)^GF2_8_mult(0x0E,a1)^
		     GF2_8_mult(0x0B,a2)^GF2_8_mult(0x0D,a3);
		b2 = GF2_8_mult(0x0D,a0)^GF2_8_mult(0x09,a1)^
		     GF2_8_mult(0x0E,a2)^GF2_8_mult(0x0B,a3);
		b3 = GF2_8_mult(0x0B,a0)^GF2_8_mult(0x0D,a1)^
		     GF2_8_mult(0x09,a2)^GF2_8_mult(0x0E,a3);

		W_ptr[4*col+0] = b0;
		W_ptr[4*col+1] = b1;
		W_ptr[4*col+2] = b2;
		W_ptr[4*col+3] = b3;
		}

	// we reverse the rounds to make decryption faster
	unsigned long * WL = reinterpret_cast<unsigned long*>(W);
	for (int pos = 0; pos < Nr/2; pos++)
		for (int col = 0; col < Nb; col++)
			swap(WL[col+pos*Nb],WL[col+(Nr-pos)*Nb]);
	} // StartDecryption

void AES::DecryptBlock(const unsigned char * datain1, unsigned char * dataout1)
	{
	unsigned long state[8*2]; // 2 buffers
	unsigned long * r_ptr = reinterpret_cast<unsigned long*>(W);
	unsigned long * dest  = state;
	unsigned long * src   = state;

	const unsigned long * datain = reinterpret_cast<const unsigned long*>(datain1);
	unsigned long * dataout = reinterpret_cast<unsigned long*>(dataout1);

	if (Nb == 4)
		{
		AddRoundKey4(dest,datain);

		if (Nr == 14)
			{
			InvRound4(dest,src);
			InvRound4(src,dest);
			InvRound4(dest,src);
			InvRound4(src,dest);
			}
		else if (Nr == 12)
			{
			InvRound4(dest,src);
			InvRound4(src,dest);
			}

		InvRound4(dest,src);
		InvRound4(src,dest);
		InvRound4(dest,src);
		InvRound4(src,dest);
		InvRound4(dest,src);
		InvRound4(src,dest);
		InvRound4(dest,src);
		InvRound4(src,dest);
		InvRound4(dest,src);

		InvFinalRound4(dataout,dest);
		}
	else if (Nb == 6)
		{
		AddRoundKey6(dest,datain);

		if (Nr == 14)
			{
			InvRound6(dest,src);
			InvRound6(src,dest);
			}

		InvRound6(dest,src);
		InvRound6(src,dest);
		InvRound6(dest,src);
		InvRound6(src,dest);
		InvRound6(dest,src);
		InvRound6(src,dest);
		InvRound6(dest,src);
		InvRound6(src,dest);
		InvRound6(dest,src);
		InvRound6(src,dest);
		InvRound6(dest,src);

		InvFinalRound6(dataout,dest);
		}
	else // Nb == 8
		{
		AddRoundKey8(dest,datain);

		InvRound8(dest,src);
		InvRound8(src,dest);
		InvRound8(dest,src);
		InvRound8(src,dest);
		InvRound8(dest,src);
		InvRound8(src,dest);
		InvRound8(dest,src);
		InvRound8(src,dest);
		InvRound8(dest,src);
		InvRound8(src,dest);
		InvRound8(dest,src);
		InvRound8(src,dest);
		InvRound8(dest,src);

		InvFinalRound8(dataout,dest);
		} // end switch on Nb
	} // Decrypt

// call this to decrypt any size block
void AES::Decrypt(const unsigned char * datain, unsigned char * dataout, unsigned long numBlocks, BlockMode mode)
	{
	if (0 == numBlocks)
		return;
	unsigned int blocksize = Nb*4;
	switch (mode)
		{
		case ECB :
			while (numBlocks)
				{
				DecryptBlock(datain,dataout);
				datain   += blocksize;
				dataout  += blocksize;
				--numBlocks;
				}
			break;
		case CBC :
			{
			int iBuf = 0;
			unsigned char buffer[2][32]; // max blocksize
			memcpy(buffer[iBuf], datain, blocksize);
			DecryptBlock(datain,dataout); // do first block
			for (unsigned int pos = 0; pos < blocksize; ++pos)
				*dataout++ ^= iv[pos];
			datain += blocksize;
			numBlocks--;

			while (numBlocks)
				{
				memcpy(buffer[iBuf^1], datain, blocksize);
				DecryptBlock(datain,dataout); // do first block
				for (unsigned int pos = 0; pos < blocksize; ++pos)
					*dataout++ ^= *(buffer[iBuf]+pos);
				datain  += blocksize;
				iBuf ^= 1;
				--numBlocks;
				}
			}
			break;
		default :
			break;
		}
	} // Decrypt

// the constructor - makes sure local things are initialized
AES::AES(void)
	{
	if (false == tablesInitialized)
		tablesInitialized = CreateAESTables(true);
	}

// end - AES.cpp