/*

This is an implementation of the AES128 algorithm, specifically ECB and CBC mode.

The implementation is verified against the test vectors in:
National Institute of Standards and Technology Special Publication 800-38A 2001 ED

ECB-AES128
----------

plain-text:
6bc1bee22e409f96e93d7e117393172a
ae2d8a571e03ac9c9eb76fac45af8e51
30c81c46a35ce411e5fbc1191a0a52ef
f69f2445df4f9b17ad2b417be66c3710

key:
2b7e151628aed2a6abf7158809cf4f3c

resulting cipher
3ad77bb40d7a3660a89ecaf32466ef97
f5d3d58503b9699de785895a96fdbaaf
43b1cd7f598ece23881b00e3ed030688
7b0c785e27e8ad3f8223207104725dd4


NOTE:   String length must be evenly divisible by 16byte (str_len % 16 == 0)
You should pad the end of the string with zeros if this is not the case.

*/


/*****************************************************************************/
/* Includes:                                                                 */
/*****************************************************************************/
#include <stdint.h>
#include <string.h> // CBC mode, for memset
#include "aes.h"


/*****************************************************************************/
/* Defines:                                                                  */
/*****************************************************************************/
// The number of columns comprising a state in AES. This is a constant in AES. Value=4
#define Nb 4
// The number of 32 bit words in a key.
#define Nk 4
// Key length in bytes [128 bit]
#define KEYLEN 16
// The number of rounds in AES Cipher.
#define Nr 10

// jcallan@github points out that declaring Multiply as a function 
// reduces code size considerably with the Keil ARM compiler.
// See this link for more information: https://github.com/kokke/tiny-AES128-C/pull/3
#ifndef MULTIPLY_AS_A_FUNCTION
#define MULTIPLY_AS_A_FUNCTION 0
#endif


/*****************************************************************************/
/* Private variables:                                                        */
/*****************************************************************************/
// state - array holding the intermediate results during decryption.
typedef uint8_t state_t[4][4];
static state_t* state;

// The array that stores the round keys.
static uint8_t RoundKey[176];

// The Key input to the AES Program
static const uint8_t* Key;

// Initial Vector used only for CBC mode
static uint8_t* Iv;


// The lookup-tables are marked const so they can be placed in read-only storage instead of RAM
// The numbers below can be computed dynamically trading ROM for RAM - 
// This can be useful in (embedded) bootloader applications, where ROM is often limited.
static const uint8_t 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 };

static const uint8_t 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 };


// 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).
static const uint8_t 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 };


/*****************************************************************************/
/* Private functions:                                                        */
/*****************************************************************************/
static uint8_t getSBoxValue(uint8_t num)
{
	return sbox[num];
}

static uint8_t getSBoxInvert(uint8_t num)
{
	return rsbox[num];
}

// This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states. 
static void KeyExpansion(void)
{
	uint32_t i, j, k;
	uint8_t tempa[4]; // Used for the column/row operations

	// The first round key is the key itself.
	for (i = 0; i < Nk; ++i)
	{
		RoundKey[(i * 4) + 0] = Key[(i * 4) + 0];
		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.
	for (; (i < (Nb * (Nr + 1))); ++i)
	{
		for (j = 0; j < 4; ++j)
		{
			tempa[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 = tempa[0];
				tempa[0] = tempa[1];
				tempa[1] = tempa[2];
				tempa[2] = tempa[3];
				tempa[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()
			{
			tempa[0] = getSBoxValue(tempa[0]);
			tempa[1] = getSBoxValue(tempa[1]);
			tempa[2] = getSBoxValue(tempa[2]);
			tempa[3] = getSBoxValue(tempa[3]);
		}

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

// This function adds the round key to state.
// The round key is added to the state by an XOR function.
static void AddRoundKey(uint8_t round)
{
	uint8_t i, j;
	for (i = 0; i<4; ++i)
	{
		for (j = 0; j < 4; ++j)
		{
			(*state)[i][j] ^= RoundKey[round * Nb * 4 + i * Nb + j];
		}
	}
}

// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
static void SubBytes(void)
{
	uint8_t i, j;
	for (i = 0; i < 4; ++i)
	{
		for (j = 0; j < 4; ++j)
		{
			(*state)[j][i] = getSBoxValue((*state)[j][i]);
		}
	}
}

// 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.
static void ShiftRows(void)
{
	uint8_t temp;

	// Rotate first row 1 columns to left  
	temp = (*state)[0][1];
	(*state)[0][1] = (*state)[1][1];
	(*state)[1][1] = (*state)[2][1];
	(*state)[2][1] = (*state)[3][1];
	(*state)[3][1] = temp;

	// Rotate second row 2 columns to left  
	temp = (*state)[0][2];
	(*state)[0][2] = (*state)[2][2];
	(*state)[2][2] = temp;

	temp = (*state)[1][2];
	(*state)[1][2] = (*state)[3][2];
	(*state)[3][2] = temp;

	// Rotate third row 3 columns to left
	temp = (*state)[0][3];
	(*state)[0][3] = (*state)[3][3];
	(*state)[3][3] = (*state)[2][3];
	(*state)[2][3] = (*state)[1][3];
	(*state)[1][3] = temp;
}

static uint8_t xtime(uint8_t x)
{
	return ((x << 1) ^ (((x >> 7) & 1) * 0x1b));
}

// MixColumns function mixes the columns of the state matrix
static void MixColumns(void)
{
	uint8_t i;
	uint8_t Tmp, Tm, t;
	for (i = 0; i < 4; ++i)
	{
		t = (*state)[i][0];
		Tmp = (*state)[i][0] ^ (*state)[i][1] ^ (*state)[i][2] ^ (*state)[i][3];
		Tm = (*state)[i][0] ^ (*state)[i][1]; Tm = xtime(Tm);  (*state)[i][0] ^= Tm ^ Tmp;
		Tm = (*state)[i][1] ^ (*state)[i][2]; Tm = xtime(Tm);  (*state)[i][1] ^= Tm ^ Tmp;
		Tm = (*state)[i][2] ^ (*state)[i][3]; Tm = xtime(Tm);  (*state)[i][2] ^= Tm ^ Tmp;
		Tm = (*state)[i][3] ^ t;        Tm = xtime(Tm);  (*state)[i][3] ^= Tm ^ Tmp;
	}
}

// Multiply is used to multiply numbers in the field GF(2^8)
#if MULTIPLY_AS_A_FUNCTION
static uint8_t Multiply(uint8_t x, uint8_t y)
{
	return (((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))))));
}
#else
#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))))))   \

#endif

// 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.
static void InvMixColumns(void)
{
	int i;
	uint8_t a, b, c, d;
	for (i = 0; i<4; ++i)
	{
		a = (*state)[i][0];
		b = (*state)[i][1];
		c = (*state)[i][2];
		d = (*state)[i][3];

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


// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
static void InvSubBytes(void)
{
	uint8_t i, j;
	for (i = 0; i<4; ++i)
	{
		for (j = 0; j<4; ++j)
		{
			(*state)[j][i] = getSBoxInvert((*state)[j][i]);
		}
	}
}

static void InvShiftRows(void)
{
	uint8_t temp;

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

	// Rotate second row 2 columns to right 
	temp = (*state)[0][2];
	(*state)[0][2] = (*state)[2][2];
	(*state)[2][2] = temp;

	temp = (*state)[1][2];
	(*state)[1][2] = (*state)[3][2];
	(*state)[3][2] = temp;

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


// Cipher is the main function that encrypts the PlainText.
static void Cipher(void)
{
	uint8_t round = 0;

	// Add the First round key to the state before starting the rounds.
	AddRoundKey(0);

	// 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();
		ShiftRows();
		MixColumns();
		AddRoundKey(round);
	}

	// The last round is given below.
	// The MixColumns function is not here in the last round.
	SubBytes();
	ShiftRows();
	AddRoundKey(Nr);
}

static void InvCipher(void)
{
	uint8_t round = 0;

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

	// 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();
		InvSubBytes();
		AddRoundKey(round);
		InvMixColumns();
	}

	// The last round is given below.
	// The MixColumns function is not here in the last round.
	InvShiftRows();
	InvSubBytes();
	AddRoundKey(0);
}

static void BlockCopy(uint8_t* output, uint8_t* input)
{
	uint8_t i;
	for (i = 0; i<KEYLEN; ++i)
	{
		output[i] = input[i];
	}
}



/*****************************************************************************/
/* Public functions:                                                         */
/*****************************************************************************/

static void XorWithIv(uint8_t* buf)
{
	uint8_t i;
	for (i = 0; i < KEYLEN; ++i)
	{
		buf[i] ^= Iv[i];
	}
}

void AES128_CBC_encrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv)
{
	intptr_t i;
	uint8_t remainders = length % KEYLEN; /* Remaining bytes in the last non-full block */

	BlockCopy(output, input);
	state = (state_t*)output;

	// Skip the key expansion if key is passed as 0
	if (0 != key)
	{
		Key = key;
		KeyExpansion();
	}

	if (iv != 0)
	{
		Iv = (uint8_t*)iv;
	}

	for (i = 0; i < length; i += KEYLEN)
	{
		XorWithIv(input);
		BlockCopy(output, input);
		state = (state_t*)output;
		Cipher();
		Iv = output;
		input += KEYLEN;
		output += KEYLEN;
	}

	if (remainders)
	{
		BlockCopy(output, input);
		memset(output + remainders, 0, KEYLEN - remainders); /* add 0-padding */
		state = (state_t*)output;
		Cipher();
	}
}

void AES128_CBC_decrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv)
{
	intptr_t i;
	uint8_t remainders = length % KEYLEN; /* Remaining bytes in the last non-full block */

	BlockCopy(output, input);
	state = (state_t*)output;

	// Skip the key expansion if key is passed as 0
	if (0 != key)
	{
		Key = key;
		KeyExpansion();
	}

	// If iv is passed as 0, we continue to encrypt without re-setting the Iv
	if (iv != 0)
	{
		Iv = (uint8_t*)iv;
	}

	for (i = 0; i < length; i += KEYLEN)
	{
		BlockCopy(output, input);
		state = (state_t*)output;
		InvCipher();
		XorWithIv(output);
		Iv = input;
		input += KEYLEN;
		output += KEYLEN;
	}

	if (remainders)
	{
		BlockCopy(output, input);
		memset(output + remainders, 0, KEYLEN - remainders); /* add 0-padding */
		state = (state_t*)output;
		InvCipher();
	}
}


