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Implemented functions: invert_sub_bytes, invert_shift_rows, invert_mi…
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…x_columns
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lin committed Apr 5, 2024
1 parent 414ef29 commit d65148f
Showing 1 changed file with 126 additions and 51 deletions.
177 changes: 126 additions & 51 deletions rijndael.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@

#include <stdlib.h> // for malloc, free
// TODO: Any other files you need to include should go here
#include <string.h>

#include "rijndael.h"

Expand Down Expand Up @@ -48,7 +49,7 @@ unsigned char s_box[256] = {
0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16}; // F

// Implementation: Rijndael S-box
unsigned char rsbox[256] = {
unsigned char r_sbox[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,
Expand Down Expand Up @@ -99,7 +100,7 @@ void shift_rows(unsigned char *block) {
// TODO: This function performs the ShiftRows transformation during
// encryption. Declare a temporary block to store intermediate results
unsigned char temp_block[BLOCK_SIZE];
// Iterate over each row in the state
// Iterate over each row in the block
for (int i = 0; i < BLOCK_SIZE; i += 4) {
// Perform row shifting with diagonal effect
// Shift the first byte in the row, no shift for the first column
Expand All @@ -118,6 +119,67 @@ void shift_rows(unsigned char *block) {
}
}

// Declaration of galois_multiplication function
unsigned char galois_multiplication(unsigned char a, unsigned char b);
// Declaration of mixColumn function
void mixColumn(unsigned char *column);
/* MixColumns operates on the columns of the block,
treating each column as a four-term polynomial and multiplying it
with a fixed polynomial modulo a predefined polynomial.
*/
void mix_columns(unsigned char *block) {
// TODO: This function performs the MixColumns
// transformation during encryption.

// Define an array to store one column of data
unsigned char column[4];

// Iterate over the 4 columns of the block matrix
for (int i = 0; i < 4; i++) {
// Construct one column by iterating over the 4 rows
for (int j = 0; j < 4; j++) {
// Fill the column array with values from the block matrix
column[j] = block[(j * 4) + i];
}

// Apply the MixColumn operation on one column
mixColumn(column);

// Put the values back into the block matrix
for (int j = 0; j < 4; j++) {
// Update the block matrix with the modified column
block[(j * 4) + i] = column[j];
}
}
}

// Function to perform MixColumn operation on a single column
void mixColumn(unsigned char *column) {
// Create a copy of the column
unsigned char cpy[4];
int i;
// Copy the values from the original column to the copy
for (i = 0; i < 4; i++) {
cpy[i] = column[i];
}
// Use Galois Field multiplication to perform the MixColumn operation
column[0] =
galois_multiplication(cpy[0], 2) ^ galois_multiplication(cpy[3], 1) ^
galois_multiplication(cpy[2], 1) ^ galois_multiplication(cpy[1], 3);

column[1] =
galois_multiplication(cpy[1], 2) ^ galois_multiplication(cpy[0], 1) ^
galois_multiplication(cpy[3], 1) ^ galois_multiplication(cpy[2], 3);

column[2] =
galois_multiplication(cpy[2], 2) ^ galois_multiplication(cpy[1], 1) ^
galois_multiplication(cpy[0], 1) ^ galois_multiplication(cpy[3], 3);

column[3] =
galois_multiplication(cpy[3], 2) ^ galois_multiplication(cpy[2], 1) ^
galois_multiplication(cpy[1], 1) ^ galois_multiplication(cpy[0], 3);
}

// Function to perform Galois Field (GF) multiplication
unsigned char galois_multiplication(unsigned char a, unsigned char b) {
// Initialize the product to 0
Expand Down Expand Up @@ -147,76 +209,85 @@ unsigned char galois_multiplication(unsigned char a, unsigned char b) {
return p;
}

// Function to perform MixColumn operation on a single column
void mixColumn(unsigned char *column) {
// Create a copy of the column
unsigned char cpy[4];
int i;
// Copy the values from the original column to the copy
for (i = 0; i < 4; i++) {
cpy[i] = column[i];
/*
* Operations used when decrypting a block
*/
void invert_sub_bytes(unsigned char *block) {
// TODO: This function performs the inverse of the SubBytes transformation
// during decryption.
for (int i = 0; i < BLOCK_SIZE; i++) {
block[i] = r_sbox[block[i]];
}
// Use Galois Field multiplication to perform the MixColumn operation
column[0] =
galois_multiplication(cpy[0], 2) ^ galois_multiplication(cpy[3], 1) ^
galois_multiplication(cpy[2], 1) ^ galois_multiplication(cpy[1], 3);
}

column[1] =
galois_multiplication(cpy[1], 2) ^ galois_multiplication(cpy[0], 1) ^
galois_multiplication(cpy[3], 1) ^ galois_multiplication(cpy[2], 3);
void invert_shift_rows(unsigned char *block) {
// TODO: undoes the row shifts performed in ShiftRows.
unsigned char temp_block[BLOCK_SIZE];

column[2] =
galois_multiplication(cpy[2], 2) ^ galois_multiplication(cpy[1], 1) ^
galois_multiplication(cpy[0], 1) ^ galois_multiplication(cpy[3], 3);
for (int i = 0; i < BLOCK_SIZE; i += 4) {
// incrementing by 5 causes the diagonal shift effect
temp_block[i] = block[i];
temp_block[(i + 5) % BLOCK_SIZE] = block[i + 1];
temp_block[(i + 10) % BLOCK_SIZE] = block[i + 2];
temp_block[(i + 15) % BLOCK_SIZE] = block[i + 3];
}

column[3] =
galois_multiplication(cpy[3], 2) ^ galois_multiplication(cpy[2], 1) ^
galois_multiplication(cpy[1], 1) ^ galois_multiplication(cpy[0], 3);
for (int i = 0; i < BLOCK_SIZE; i++) {
block[i] = temp_block[i];
}
}

/* MixColumns operates on the columns of the block,
treating each column as a four-term polynomial and multiplying it
with a fixed polynomial modulo a predefined polynomial.
*/
void mix_columns(unsigned char *block) {
// TODO: This function performs the MixColumns
// transformation during encryption.
int i, j;
// Declaration of invert_mix_column function
void invert_mix_column(unsigned char *column);

void invert_mix_columns(unsigned char *block) {
// TODO: undoes the column mixing performed in MixColumns.
// Define an array to store one column of data
unsigned char column[4];

// Iterate over the 4 columns of the state matrix
for (i = 0; i < 4; i++) {
// Iterate over the 4 columns of the block matrix
for (int i = 0; i < 4; i++) {
// Construct one column by iterating over the 4 rows
for (j = 0; j < 4; j++) {
// Fill the column array with values from the state matrix
for (int j = 0; j < 4; j++) {
// Fill the column array with values from the block matrix
column[j] = block[(j * 4) + i];
}

// Apply the MixColumn operation on one column
mixColumn(column);
// Apply the InvertMixColumn operation on one column
invert_mix_column(column);

// Put the values back into the state matrix
for (j = 0; j < 4; j++) {
// Update the state matrix with the modified column
// Put the values back into the block matrix
for (int j = 0; j < 4; j++) {
// Update the block matrix with the modified column
block[(j * 4) + i] = column[j];
}
}
}

/*
* Operations used when decrypting a block
*/
void invert_sub_bytes(unsigned char *block) {
// TODO: Implement me!
}
// Function to perform InvertMixColumn operation on a single column
void invert_mix_column(unsigned char *column) {
// Create a copy of the column
unsigned char cpy[4];
// Copy the values from the original column to the copy
for (int i = 0; i < 4; i++) {
cpy[i] = column[i];
}
// Use Galois Field multiplication to perform the InvertMixColumn operation
column[0] =
galois_multiplication(cpy[0], 14) ^ galois_multiplication(cpy[3], 9) ^
galois_multiplication(cpy[2], 13) ^ galois_multiplication(cpy[1], 11);

void invert_shift_rows(unsigned char *block) {
// TODO: Implement me!
}
column[1] =
galois_multiplication(cpy[1], 14) ^ galois_multiplication(cpy[0], 9) ^
galois_multiplication(cpy[3], 13) ^ galois_multiplication(cpy[2], 11);

void invert_mix_columns(unsigned char *block) {
// TODO: Implement me!
column[2] =
galois_multiplication(cpy[2], 14) ^ galois_multiplication(cpy[1], 9) ^
galois_multiplication(cpy[0], 13) ^ galois_multiplication(cpy[3], 11);

column[3] =
galois_multiplication(cpy[3], 14) ^ galois_multiplication(cpy[2], 9) ^
galois_multiplication(cpy[1], 13) ^ galois_multiplication(cpy[0], 11);
}

/*
Expand All @@ -241,6 +312,10 @@ void key_schedule_core(unsigned char *word, int iteration);
*/
unsigned char *expand_key(unsigned char *cipher_key) {
// TODO: Implementation of key expansion function
// 1.ExpandKey takes the original cipher key and
// generates a series of round keys using a key schedule algorithm.
// 2.These round keys are derived from the original key and are used
// in each round of encryption and decryption.
if (cipher_key == NULL) {
printf("Error: Cipher key is NULL.\n");
return NULL;
Expand Down

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