/*
   This code is a Parallel Implementation of the 
   source code available at http://comp.ist.utl.pt/ec-csc/Code/Ciphers/AES_Encrypt.cpp
*/

#include<stdio.h>
#include<omp.h>
#include<string.h>

#define KB 1024
#define MB 1024*1024
#define CHUNK_SIZE 256*KB
#define KEY_LENGTH 128 
// The number of columns comprising a state in AES. This is a constant in AES. Value=4
#define Nb 4

// The number of rounds in AES Cipher. It is simply initiated to zero. The actual value is recieved in the program.
int Nr=0;

// The number of 32 bit words in the key. It is simply initiated to zero. The actual value is recieved in the program.
int Nk=0;


// The array that stores the round keys.
unsigned char RoundKey[240];

// The Key input to the AES Program
unsigned char Key[32];

int getSBoxValue(int num)
{
	int sbox[256] =   {
	//0     1    2      3     4    5     6     7      8    9     A      B    C     D     E     F
	0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, //0
	0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, //1
	0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, //2
	0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, //3
	0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, //4
	0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, //5
	0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, //6
	0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, //7
	0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, //8
	0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, //9
	0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, //A
	0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, //B
	0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, //C
	0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, //D
	0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, //E
	0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 }; //F
	return sbox[num];
}

// The round constant word array, Rcon[i], contains the values given by 
// x to th e power (i-1) being powers of x (x is denoted as {02}) in the field GF(28)
// Note that i starts at 1, not 0).
int Rcon[255] = {
	0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 
	0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 
	0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 
	0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 
	0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 
	0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 
	0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 
	0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 
	0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 
	0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 
	0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 
	0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 
	0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 
	0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 
	0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 
	0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb  };

// This function produces Nb(Nr+1) round keys. The round keys are used in each round to encrypt the states. 
void KeyExpansion()
{
	int i,j;
	unsigned char temp[4],k;
	
	// The first round key is the key itself.
	for(i=0;i<Nk;i++)
	{
		RoundKey[i*4]=Key[i*4];
		RoundKey[i*4+1]=Key[i*4+1];
		RoundKey[i*4+2]=Key[i*4+2];
		RoundKey[i*4+3]=Key[i*4+3];
	}

	// All other round keys are found from the previous round keys.
	while (i < (Nb * (Nr+1)))
	{
					for(j=0;j<4;j++)
					{
						temp[j]=RoundKey[(i-1) * 4 + j];
					}
					if (i % Nk == 0)
					{
						// This function rotates the 4 bytes in a word to the left once.
						// [a0,a1,a2,a3] becomes [a1,a2,a3,a0]

						// Function RotWord()
						{
							k = temp[0];
							temp[0] = temp[1];
							temp[1] = temp[2];
							temp[2] = temp[3];
							temp[3] = k;
						}

						// SubWord() is a function that takes a four-byte input word and 
						// applies the S-box to each of the four bytes to produce an output word.

						// Function Subword()
						{
							temp[0]=getSBoxValue(temp[0]);
							temp[1]=getSBoxValue(temp[1]);
							temp[2]=getSBoxValue(temp[2]);
							temp[3]=getSBoxValue(temp[3]);
						}

						temp[0] =  temp[0] ^ Rcon[i/Nk];
					}
					else if (Nk > 6 && i % Nk == 4)
					{
						// Function Subword()
						{
							temp[0]=getSBoxValue(temp[0]);
							temp[1]=getSBoxValue(temp[1]);
							temp[2]=getSBoxValue(temp[2]);
							temp[3]=getSBoxValue(temp[3]);
						}
					}
					RoundKey[i*4+0] = RoundKey[(i-Nk)*4+0] ^ temp[0];
					RoundKey[i*4+1] = RoundKey[(i-Nk)*4+1] ^ temp[1];
					RoundKey[i*4+2] = RoundKey[(i-Nk)*4+2] ^ temp[2];
					RoundKey[i*4+3] = RoundKey[(i-Nk)*4+3] ^ temp[3];
					i++;
	}
}

// This function adds the round key to state.
// The round key is added to the state by an XOR function.
void AddRoundKey(int round, unsigned char state[][4]) 
{
	int i,j;
	for(i=0;i<4;i++)
   {
		for(j=0;j<4;j++)
		{
			state[j][i] ^= RoundKey[round * Nb * 4 + i * Nb + j];
		}
	}
}

// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
void SubBytes(unsigned char state[][4])
{
	int i,j;
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++)
		{
			state[i][j] = getSBoxValue(state[i][j]);

		}
	}
}

// The ShiftRows() function shifts the rows in the state to the left.
// Each row is shifted with different offset.
// Offset = Row number. So the first row is not shifted.
void ShiftRows(unsigned char state[][4])
{
	unsigned char temp;
   	// Rotate first row 1 columns to left	
         temp=state[1][0];
         state[1][0]=state[1][1];
         state[1][1]=state[1][2];
         state[1][2]=state[1][3];
         state[1][3]=temp;
      // Rotate second row 2 columns to left	

         temp=state[2][0];
         state[2][0]=state[2][2];
         state[2][2]=temp;

         temp=state[2][1];
         state[2][1]=state[2][3];
         state[2][3]=temp;
      // Rotate third row 3 columns to left

         temp=state[3][0];
         state[3][0]=state[3][3];
         state[3][3]=state[3][2];
         state[3][2]=state[3][1];
         state[3][1]=temp;
}

// xtime is a macro that finds the product of {02} and the argument to xtime modulo {1b}  
#define xtime(x)   ((x<<1) ^ (((x>>7) & 1) * 0x1b))

// MixColumns function mixes the columns of the state matrix
void MixColumns(unsigned char state[][4])
{
	int i;
	unsigned char Tmp,Tm,t;
	for(i=0;i<4;i++)
	{	
		t=state[0][i];
		Tmp = state[0][i] ^ state[1][i] ^ state[2][i] ^ state[3][i] ;
		Tm = state[0][i] ^ state[1][i] ; Tm = xtime(Tm); state[0][i] ^= Tm ^ Tmp ;
		Tm = state[1][i] ^ state[2][i] ; Tm = xtime(Tm); state[1][i] ^= Tm ^ Tmp ;
		Tm = state[2][i] ^ state[3][i] ; Tm = xtime(Tm); state[2][i] ^= Tm ^ Tmp ;
		Tm = state[3][i] ^ t ; Tm = xtime(Tm); state[3][i] ^= Tm ^ Tmp ;
	}
}

// in - is the array that holds the plain text to be encrypted.
// out -is the array that holds the key for encryption.
// state - the array that holds the intermediate results during encryption.
// Cipher is the main function that encrypts the PlainText.
void Cipher(unsigned char *in, unsigned char *out)
{
	int i,j,round=0;
   unsigned char state[4][4];
	//Copy the input PlainText to state array.
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++){
		
			state[j][i] = in[i*4 + j];
		}
	}

	// Add the First round key to the state before starting the rounds.
	AddRoundKey(0, state); 
	
	// There will be Nr rounds.
	// The first Nr-1 rounds are identical.
	// These Nr-1 rounds are executed in the loop below.
	for(round=1;round<Nr;round++)
	{
		SubBytes(state);
		ShiftRows(state);
		MixColumns(state);
		AddRoundKey(round, state);
	}
	
	// The last round is given below.
	// The MixColumns function is not here in the last round.
	SubBytes(state);
	ShiftRows(state);
	AddRoundKey(Nr, state);

	// The encryption process is over.
	// Copy the state array to output array.
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++)
		{
			out[i*4+j]=state[j][i];
		}
	}
}
int main(int argc, char* argv[])
{
	int i;

	// Recieve the length of key here.
	while(Nr!=128 && Nr!=192 && Nr!=256)
	{
		printf("Enter the length of Key(128, 192 or 256 only): ");
		scanf("%d",&Nr);
	}
   //Nr = KEY_LENGTH;
	
	// Calculate Nk and Nr from the recieved value.
	Nk = Nr / 32;
	Nr = Nk + 6;



	// The array temp_key stores the key.
	unsigned char temp_key[32] = {0x00  ,0x01  ,0x02  ,0x03  ,0x04  ,0x05  ,0x06  ,0x07  ,0x08  ,0x09  ,0x0a  ,0x0b  ,0x0c  ,0x0d  ,0x0e  ,0x0f};
	
	// Copy the Key
	for(i=0;i<Nk*4;i++)
		Key[i]=temp_key[i];

//   ****************
// FILE READING CAPABILITY

   FILE *fp_input = fopen(argv[1], "rb");
   FILE *fp_output = fopen(argv[2], "ab");      
   char chunk_input[CHUNK_SIZE];
   char chunk_output[CHUNK_SIZE];
   // The KeyExpansion routine must be called before encryption.
   KeyExpansion();
   while(fread(chunk_input, sizeof(chunk_input), 1, fp_input) == 1){ 
      //DO OPERATIONS
      int i = 0;      
      #pragma omp parallel for private(i)
      for(i=0; i<CHUNK_SIZE; i += 16){
         unsigned char in[16], out[16];
         int block_no = i;
         memcpy(in, &chunk_input[block_no], 16);
         //The next function call encrypts the PlainText with the Key using AES algorithm.
         Cipher(in, out);
         memcpy(&chunk_output[block_no], out, 16);
      }
      
      fwrite(chunk_output, sizeof(chunk_output), 1, fp_output);
      
   }
   fclose(fp_output);
   fclose(fp_input);

   printf("Encryption of file %s complete. \n ", argv[1]);
   
}

description.cpp

/*
   This code is a parallel implementation of the source code available
   at http://comp.ist.utl.pt/ec-csc/Code/Ciphers/AES_Decrypt.cpp
*/

#include<stdio.h>
#include<omp.h>
#include<string.h>
#define KB 1024
#define MB 1024*1024
#define CHUNK_SIZE 256*KB
#define KEY_LENGTH 128 

// The number of columns comprising a state in AES. This is a constant in AES. Value=4
#define Nb 4

// The number of rounds in AES Cipher. It is simply initiated to zero. The actual value is recieved in the program.
int Nr=0;

// The number of 32 bit words in the key. It is simply initiated to zero. The actual value is recieved in the program.
int Nk=0;


// The array that stores the round keys.
unsigned char RoundKey[240];

// The Key input to the AES Program
unsigned char Key[32];

int getSBoxInvert(int num)
{
int rsbox[256] =
{ 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb
, 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb
, 0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e
, 0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25
, 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92
, 0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84
, 0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06
, 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b
, 0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73
, 0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e
, 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b
, 0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4
, 0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f
, 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef
, 0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61
, 0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d };

return rsbox[num];
}

int getSBoxValue(int num)
{
	int sbox[256] =   {
	//0     1    2      3     4    5     6     7      8    9     A      B    C     D     E     F
	0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
	0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
	0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
	0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
	0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
	0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
	0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
	0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
	0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
	0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
	0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
	0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
	0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
	0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
	0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
	0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 };
	return sbox[num];
}

// The round constant word array, Rcon[i], contains the values given by 
// x to th e power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
// Note that i starts at 1, not 0).
int Rcon[255] = {
	0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 
	0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 
	0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 
	0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 
	0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 
	0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 
	0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 
	0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 
	0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 
	0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 
	0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 
	0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 
	0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 
	0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 
	0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 
	0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb  };

// This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states. 
void KeyExpansion()
{
	int i,j;
	unsigned char temp[4],k;
	
	// The first round key is the key itself.
	for(i=0;i<Nk;i++)
	{
		RoundKey[i*4]=Key[i*4];
		RoundKey[i*4+1]=Key[i*4+1];
		RoundKey[i*4+2]=Key[i*4+2];
		RoundKey[i*4+3]=Key[i*4+3];
	}

	// All other round keys are found from the previous round keys.
	while (i < (Nb * (Nr+1)))
	{
		for(j=0;j<4;j++)
		{
			temp[j]=RoundKey[(i-1) * 4 + j];
		}
		if (i % Nk == 0)
		{
			// This function rotates the 4 bytes in a word to the left once.
			// [a0,a1,a2,a3] becomes [a1,a2,a3,a0]

			// Function RotWord()
			{
				k = temp[0];
				temp[0] = temp[1];
				temp[1] = temp[2];
				temp[2] = temp[3];
				temp[3] = k;
			}

			// SubWord() is a function that takes a four-byte input word and 
			// applies the S-box to each of the four bytes to produce an output word.

			// Function Subword()
			{
				temp[0]=getSBoxValue(temp[0]);
				temp[1]=getSBoxValue(temp[1]);
				temp[2]=getSBoxValue(temp[2]);
				temp[3]=getSBoxValue(temp[3]);
			}

			temp[0] =  temp[0] ^ Rcon[i/Nk];
		}
		else if (Nk > 6 && i % Nk == 4)
		{
			// Function Subword()
			{
				temp[0]=getSBoxValue(temp[0]);
				temp[1]=getSBoxValue(temp[1]);
				temp[2]=getSBoxValue(temp[2]);
				temp[3]=getSBoxValue(temp[3]);
			}
		}
		RoundKey[i*4+0] = RoundKey[(i-Nk)*4+0] ^ temp[0];
		RoundKey[i*4+1] = RoundKey[(i-Nk)*4+1] ^ temp[1];
		RoundKey[i*4+2] = RoundKey[(i-Nk)*4+2] ^ temp[2];
		RoundKey[i*4+3] = RoundKey[(i-Nk)*4+3] ^ temp[3];
		i++;
	}
}

// This function adds the round key to state.
// The round key is added to the state by an XOR function.
void AddRoundKey(int round, unsigned char state[][4]) 
{
	int i,j;
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++)
		{
			state[j][i] ^= RoundKey[round * Nb * 4 + i * Nb + j];
		}
	}
}

// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
void InvSubBytes(unsigned char state[][4])
{
	int i,j;
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++)
		{
			state[i][j] = getSBoxInvert(state[i][j]);

		}
	}
}

// The ShiftRows() function shifts the rows in the state to the left.
// Each row is shifted with different offset.
// Offset = Row number. So the first row is not shifted.
void InvShiftRows(unsigned char state[][4])
{
	unsigned char temp;

	// Rotate first row 1 columns to right	
            temp=state[1][3];
            state[1][3]=state[1][2];
            state[1][2]=state[1][1];
            state[1][1]=state[1][0];
            state[1][0]=temp;
            // Rotate second row 2 columns to right	
            
            temp=state[2][0];
            state[2][0]=state[2][2];
            state[2][2]=temp;

            temp=state[2][1];
            state[2][1]=state[2][3];
            state[2][3]=temp;
            // Rotate third row 3 columns to right
            
            temp=state[3][0];
            state[3][0]=state[3][1];
            state[3][1]=state[3][2];
            state[3][2]=state[3][3];
            state[3][3]=temp;
}

// xtime is a macro that finds the product of {02} and the argument to xtime modulo {1b}  
#define xtime(x)   ((x<<1) ^ (((x>>7) & 1) * 0x1b))

// Multiplty is a macro used to multiply numbers in the field GF(2^8)
#define Multiply(x,y) (((y & 1) * x) ^ ((y>>1 & 1) * xtime(x)) ^ ((y>>2 & 1) * xtime(xtime(x))) ^ ((y>>3 & 1) * xtime(xtime(xtime(x)))) ^ ((y>>4 & 1) * xtime(xtime(xtime(xtime(x))))))

// MixColumns function mixes the columns of the state matrix.
// The method used to multiply may be difficult to understand for the inexperienced.
// Please use the references to gain more information.
void InvMixColumns(unsigned char state[][4])
{
	int i;
	unsigned char a,b,c,d;
	for(i=0;i<4;i++)
	{	
	
		a = state[0][i];
		b = state[1][i];
		c = state[2][i];
		d = state[3][i];

		
		state[0][i] = Multiply(a, 0x0e) ^ Multiply(b, 0x0b) ^ Multiply(c, 0x0d) ^ Multiply(d, 0x09);
		state[1][i] = Multiply(a, 0x09) ^ Multiply(b, 0x0e) ^ Multiply(c, 0x0b) ^ Multiply(d, 0x0d);
		state[2][i] = Multiply(a, 0x0d) ^ Multiply(b, 0x09) ^ Multiply(c, 0x0e) ^ Multiply(d, 0x0b);
		state[3][i] = Multiply(a, 0x0b) ^ Multiply(b, 0x0d) ^ Multiply(c, 0x09) ^ Multiply(d, 0x0e);
	}
}

// InvCipher is the main function that decrypts the CipherText.
void InvCipher(unsigned char *in, unsigned char *out)
{
	int i,j,round=0;
	unsigned char state[4][4];
	//Copy the input CipherText to state array.
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++)
		{
			state[j][i] = in[i*4 + j];
		}
	}

	// Add the First round key to the state before starting the rounds.
	AddRoundKey(Nr, state); 

	// There will be Nr rounds.
	// The first Nr-1 rounds are identical.
	// These Nr-1 rounds are executed in the loop below.
	for(round=Nr-1;round>0;round--)
	{
		InvShiftRows(state);
		InvSubBytes(state);
		AddRoundKey(round, state);
		InvMixColumns(state);
	}
	
	// The last round is given below.
	// The MixColumns function is not here in the last round.
	InvShiftRows(state);
	InvSubBytes(state);
	AddRoundKey(0, state);

	// The decryption process is over.
	// Copy the state array to output array.
	for(i=0;i<4;i++)
	{
		for(j=0;j<4;j++)
		{
			out[i*4+j]=state[j][i];
		}
	}
}
int main(int argc, char* argv[])
{
	int i;

	// Recieve the length of key here.
	while(Nr!=128 && Nr!=192 && Nr!=256)
	{
		printf("Enter the length of Key(128, 192 or 256 only): ");
		scanf("%d",&Nr);
	}
	// Calculate Nk and Nr from the recieved value.
	Nk = Nr / 32;
	Nr = Nk + 6;



// Part 1 is for demonstrative purpose. The key and plaintext are given in the program itself.
// 	Part 1: ********************************************************
	
	// The array temp stores the key.
	// The array temp2 stores the plaintext.
	unsigned char temp[32] = {0x00  ,0x01  ,0x02  ,0x03  ,0x04  ,0x05  ,0x06  ,0x07  ,0x08  ,0x09  ,0x0a  ,0x0b  ,0x0c  ,0x0d  ,0x0e  ,0x0f};
	
	// Copy the Key and CipherText
	for(i=0;i<Nk*4;i++)
		Key[i]=temp[i];

//	       *********************************************************

//FILE READ AND WRITE FOLLOWS

   FILE *fp_input = fopen(argv[1], "rb");
   FILE *fp_output = fopen(argv[2], "ab");
   unsigned char source[CHUNK_SIZE];
   char chunk_input[CHUNK_SIZE];
   char chunk_output[CHUNK_SIZE];

   //The Key-Expansion routine must be called before the decryption routine.
   KeyExpansion();

   while(fread(chunk_input, sizeof(chunk_input), 1, fp_input) == 1){ 
      //DO OPERATIONS
      int i = 0;      
      #pragma omp parallel for private(i)
      for(i=0; i<CHUNK_SIZE; i += 16){
         unsigned char in[16], out[16];
         int block_no = i;
         memcpy(in, &chunk_input[block_no], 16);
         //The next function call decrypts the PlainText with the Key using AES algorithm.
         InvCipher(in, out);
         memcpy(&chunk_output[block_no], out, 16);
      }
      
      fwrite(chunk_output, sizeof(chunk_output), 1, fp_output);
      
   }
   fclose(fp_output);
   fclose(fp_input);
}