/*
 * Copyright (c) 2024, ArtInChip Technology Co., Ltd
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <string.h>
#include <stdio.h>
#include "soft-aes-ecb.h"

// The number of columns comprising a state in AES. This is a constant in AES. Value=4
#define Nb 4
#define Nk 4 // The number of 32 bit words in a key.
#define Nr 10 // The number of rounds in AES cipher.

// state - array holding the intermediate results during decryption.
typedef unsigned char state_t[4][4];

// 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 unsigned char 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 unsigned char 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 the power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
static const unsigned char Rcon[11] = {
  0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36 };

/*
 * Jordan Goulder points out in PR #12 (https://github.com/kokke/tiny-AES-C/pull/12),
 * that you can remove most of the elements in the Rcon array, because they are unused.
 *
 * From Wikipedia's article on the Rijndael key schedule @ https://en.wikipedia.org/wiki/Rijndael_key_schedule#Rcon
 * 
 * "Only the first some of these constants are actually used – up to rcon[10] for AES-128 (as 11 round keys are needed), 
 *  up to rcon[8] for AES-192, up to rcon[7] for AES-256. rcon[0] is not used in AES algorithm."
 */

#define get_sbox_value(num) (sbox[(num)])


// This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states.
static void key_expansion(unsigned char *round_key, const unsigned char *Key)
{
	unsigned i, j, k;
	unsigned char tempa[4]; // Used for the column/row operations

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

	// All other round keys are found from the previous round keys.
    for (i = Nk; i < Nb * (Nr + 1); ++i) {
        k = (i - 1) * 4;
        tempa[0] = round_key[k + 0];
        tempa[1] = round_key[k + 1];
        tempa[2] = round_key[k + 2];
        tempa[3] = round_key[k + 3];

        if (i % Nk == 0) {
			// This function shifts the 4 bytes in a word to the left once.
			// [a0,a1,a2,a3] becomes [a1,a2,a3,a0]

			// Function RotWord()
            const unsigned char u8tmp = tempa[0];
            tempa[0] = tempa[1];
            tempa[1] = tempa[2];
            tempa[2] = tempa[3];
            tempa[3] = u8tmp;

			// 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] = get_sbox_value(tempa[0]);
            tempa[1] = get_sbox_value(tempa[1]);
            tempa[2] = get_sbox_value(tempa[2]);
            tempa[3] = get_sbox_value(tempa[3]);

			tempa[0] = tempa[0] ^ Rcon[i / Nk];
		}
		j = i * 4;
		k = (i - Nk) * 4;
		round_key[j + 0] = round_key[k + 0] ^ tempa[0];
		round_key[j + 1] = round_key[k + 1] ^ tempa[1];
		round_key[j + 2] = round_key[k + 2] ^ tempa[2];
		round_key[j + 3] = round_key[k + 3] ^ tempa[3];
    }
}

void aes_init_ctx(struct aes_ctx *ctx, const unsigned char *key)
{
	key_expansion(ctx->round_key, key);
}

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

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

// The shift_rows() 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 shift_rows(state_t *state)
{
	unsigned char 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 unsigned char xtime(unsigned char x)
{
	return ((x << 1) ^ (((x >> 7) & 1) * 0x1b));
}

// mix_columns function mixes the columns of the state matrix
static void mix_columns(state_t *state)
{
	unsigned char i;
	unsigned char 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)
// Note: The last call to xtime() is unneeded, but often ends up generating a smaller binary
//       The compiler seems to be able to vectorize the operation better this way.
//       See https://github.com/kokke/tiny-AES-c/pull/34
#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))))))   \

#define get_sbox_invert(num) (rsbox[(num)])

// mix_columns 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 inv_mix_columns(state_t *state)
{
	int i;
	unsigned char 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 sub_bytes Function Substitutes the values in the
// state matrix with values in an S-box.
static void inv_sub_bytes(state_t *state)
{
	unsigned char i, j;
	for (i = 0; i < 4; ++i) {
		for (j = 0; j < 4; ++j) {
			(*state)[j][i] = get_sbox_invert((*state)[j][i]);
		}
	}
}

static void inv_shift_rows(state_t *state)
{
	unsigned char 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(state_t *state, const unsigned char *round_key)
{
	unsigned char round = 0;

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

	// There will be Nr rounds.
	// The first Nr-1 rounds are identical.
	// These Nr rounds are executed in the loop below.
	// Last one without mix_columns()
	for (round = 1;; ++round) {
		sub_bytes(state);
		shift_rows(state);
		if (round == Nr) {
			break;
		}
		mix_columns(state);
		add_round_key(round, state, round_key);
	}
	// Add round key to last round
	add_round_key(Nr, state, round_key);
}

static void inv_cipher(state_t *state, const unsigned char *round_key)
{
	unsigned char round = 0;

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

	// There will be Nr rounds.
	// The first Nr-1 rounds are identical.
	// These Nr rounds are executed in the loop below.
	// Last one without InvMixColumn()
	for (round = (Nr - 1);; --round) {
		inv_shift_rows(state);
		inv_sub_bytes(state);
		add_round_key(round, state, round_key);
		if (round == 0) {
			break;
		}
		inv_mix_columns(state);
	}
}

void aes_128_ecb_encrypt(const struct aes_ctx *ctx, unsigned char *buf)
{
	// The next function call encrypts the PlainText with the Key using AES algorithm.
	cipher((state_t *)buf, ctx->round_key);
}

void aes_128_ecb_decrypt(const struct aes_ctx *ctx, unsigned char *buf)
{
	// The next function call decrypts the PlainText with the Key using AES algorithm.
	inv_cipher((state_t *)buf, ctx->round_key);
}