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Add AES C code used to debug Chapter 18 K additions

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James Stine 2025-04-07 13:11:24 -05:00
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13
examples/crypto/aes/Makefile Normal file
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CC = gcc
CFLAGS = -g
all: aes
aes: aes.c
$(CC) $(CFLAGS) aes.c -o aes
clean:
rm -rf aes
rm -f *~
.PHONY: all clean

641
examples/crypto/aes/aes.c Normal file
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//
// aes.c
// Modified based on ideas from https://github.com/m3y54m/aes-in-c.git and FIPS 197
// james.stine@okstate.edu 11 October 2024
//
#include <stdio.h>
#include <stdlib.h>
enum errorCode {
SUCCESS = 0,
ERROR_AES_UNKNOWN_KEYSIZE,
ERROR_MEMORY_ALLOCATION_FAILED,
};
// Implementation: S-Box (page 14 FIPS 197 Table 4)
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, // 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
// inverse S-box used in the InvSubBytes() (page 23 FIPS 197 Table 6)
unsigned char rsbox[256] =
// 0 1 2 3 4 5 6 7 8 9 A B C D E F
{0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb, // 0
0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb, // 1
0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e, // 2
0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25, // 3
0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, // 4
0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84, // 5
0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06, // 6
0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, // 7
0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73, // 8
0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e, // 9
0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, // A
0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4, // B
0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f, // C
0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, // D
0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61, // E
0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d}; // F
// Implementation: Rcon (Round constants) - help introduce non-linearity and prevent symmetries
// Rcon[i] = 0x02^(i-1) mod x^8 + x^4 + x^3 + x + 1
unsigned char 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};
unsigned char getRconValue(unsigned char num);
// Implementation: Key Expansion
enum keySize {
SIZE_16 = 16,
SIZE_24 = 24,
SIZE_32 = 32
};
// AES Encryption Function Prototypes
void subBytes(unsigned char *state);
void shiftRows(unsigned char *state);
void shiftRow(unsigned char *state, unsigned char nbr);
void addRoundKey(unsigned char *state, unsigned char *roundKey);
unsigned char galois_multiplication(unsigned char a, unsigned char b);
void mixColumns(unsigned char *state);
void mixColumn(unsigned char *column);
void aes_cipher(unsigned char *state, unsigned char *roundKey);
void createRoundKey(unsigned char *expandedKey, unsigned char *roundKey);
void aes_main(unsigned char *state, unsigned char *expandedKey, int nbrRounds);
char aes_encrypt(unsigned char *input, unsigned char *output, unsigned char *key, enum keySize size);
// AES Decryption Function Prototypes
void invSubBytes(unsigned char *state);
void invShiftRows(unsigned char *state);
void invShiftRow(unsigned char *state, unsigned char nbr);
void invMixColumns(unsigned char *state);
void invMixColumn(unsigned char *column);
void aes_invRound(unsigned char *state, unsigned char *roundKey);
void aes_invCipher(unsigned char *state, unsigned char *expandedKey, int nbrRounds);
char aes_decrypt(unsigned char *input, unsigned char *output, unsigned char *key, enum keySize size);
// Helper function to print AES state
void printState(const unsigned char *state) {
for (int col = 0; col < 4; col++) {
printf("%02x %02x %02x %02x ",
state[col], state[col + 4], state[col + 8], state[col + 12]);
}
printf("\n");
}
unsigned char getSBoxValue(unsigned char num) {
return sbox[num];
}
unsigned char getSBoxInvert(unsigned char num) {
return rsbox[num];
}
// left circular rotation (i.e., byte-wise rotate left) on a 4-byte word
void rotate(unsigned char *word) {
unsigned char temp = word[0];
word[0] = word[1];
word[1] = word[2];
word[2] = word[3];
word[3] = temp;
}
unsigned char getRconValue(unsigned char num) {
return Rcon[num];
}
void KeySchedule(unsigned char *word, int iteration) {
int i;
// Key Schedule: RotWord → SubWord → XOR with Rcon
// used during key expansion to transform the input word before XORing it with a
// word from earlier in the expanded key array.
// rotate the 32-bit word 8 bits to the left
rotate(word);
// apply S-Box substitution on all 4 parts of the 32-bit word
for (i = 0; i < 4; ++i) {
word[i] = getSBoxValue(word[i]);
}
// XOR the output of the rcon operation with i to the first part (leftmost) only
word[0] = word[0] ^ getRconValue(iteration);
}
// Rijndael's key expansion: expands an 128, 192, 256 key into an 176, 208, 240 bytes key
void KeyExpansion(unsigned char *expandedKey, unsigned char *key,
enum keySize size, size_t expandedKeySize) {
// current expanded keySize, in bytes
int currentSize = 0;
int rconIteration = 1;
int i;
unsigned char t[4] = {0}; // temporary 4-byte variable
// set the 16, 24,32 bytes of the expanded key to the input key
for (i = 0; i < size; i++)
expandedKey[i] = key[i];
currentSize += size;
while (currentSize < expandedKeySize) {
// assign the previous 4 bytes to the temporary value t
for (i = 0; i < 4; i++) {
t[i] = expandedKey[(currentSize - 4) + i];
}
// every 16, 24, 32 bytes we apply the core schedule to t
// and increment rconIteration afterwards
if (currentSize % size == 0) {
KeySchedule(t, rconIteration++);
}
// For 256-bit keys, we add an extra sbox to the calculation
if (size == SIZE_32 && ((currentSize % size) == 16)) {
for (i = 0; i < 4; i++)
t[i] = getSBoxValue(t[i]);
}
// We XOR t with the four-byte block 16, 24, 32 bytes before the new expanded key.
// This becomes the next four bytes in the expanded key.
for (i = 0; i < 4; i++) {
expandedKey[currentSize] = expandedKey[currentSize - size] ^ t[i];
currentSize++;
}
}
}
void subBytes(unsigned char *state) {
for (int i = 0; i < 16; i++) {
state[i] = getSBoxValue(state[i]);
}
}
void shiftRows(unsigned char *state) {
for (int row = 0; row < 4; row++) {
shiftRow(state + row * 4, row);
}
}
void shiftRow(unsigned char *state, unsigned char nbr) {
unsigned char temp[4];
// Perform rotation directly
for (int i = 0; i < 4; i++) {
temp[i] = state[(i + nbr) % 4];
}
// Copy result back to state
for (int i = 0; i < 4; i++) {
state[i] = temp[i];
}
}
void addRoundKey(unsigned char *state, unsigned char *roundKey) {
int i;
for (i = 0; i < 16; i++)
state[i] = state[i] ^ roundKey[i];
}
// Based on work by Tom St. Denis/Simon Johnson
// https://www.amazon.com/Cryptography-Developers-Tom-St-Denis/dp/1597491047
unsigned char gfmul(unsigned char a, unsigned char b) {
unsigned char p = 0;
for (unsigned char counter = 0; counter < 8; counter++) {
if (b & 1)
p ^= a;
a = (a << 1) ^ ((a & 0x80) ? 0x1b : 0);
b >>= 1;
}
return p;
}
// Section 5.1.3 of FIPS 197
void mixColumns(unsigned char *state) {
unsigned char column[4];
for (int col = 0; col < 4; col++) {
// Extract the column from the state
for (int row = 0; row < 4; row++) {
column[row] = state[row * 4 + col];
}
// Mix the column
mixColumn(column);
// Store the mixed column back into the state
for (int row = 0; row < 4; row++) {
state[row * 4 + col] = column[row];
}
}
}
void mixColumn(unsigned char *column) {
unsigned char a[4], b[4];
for (int i = 0; i < 4; i++) {
a[i] = column[i];
b[i] = gfmul(column[i], 2);
}
column[0] = b[0] ^ a[3] ^ a[2] ^ gfmul(a[1], 3);
column[1] = b[1] ^ a[0] ^ a[3] ^ gfmul(a[2], 3);
column[2] = b[2] ^ a[1] ^ a[0] ^ gfmul(a[3], 3);
column[3] = b[3] ^ a[2] ^ a[1] ^ gfmul(a[0], 3);
}
// The rounds in the specifcation of CIPHER() are composed of the following 4 byte-oriented
// transformations on the state (Section 5.1 of FIPS 197) - outputs hex after each step
void aes_cipher(unsigned char *state, unsigned char *roundKey) {
subBytes(state);
printState(state);
shiftRows(state);
printState(state);
mixColumns(state);
printState(state);
addRoundKey(state, roundKey);
printf("\n"); // Optional: for spacing
}
void createRoundKey(unsigned char *expandedKey, unsigned char *roundKey) {
int i, j;
// iterate over the columns
for (i = 0; i < 4; i++) {
// iterate over the rows
for (j = 0; j < 4; j++)
roundKey[(i + (j * 4))] = expandedKey[(i * 4) + j];
}
}
void aes_main(unsigned char *state, unsigned char *expandedKey, int nbrRounds) {
unsigned char roundKey[16];
// Initial round key
createRoundKey(expandedKey, roundKey);
printState(state);
printf("\n");
addRoundKey(state, roundKey);
for (int i = 1; i < nbrRounds; i++) {
createRoundKey(expandedKey + 16 * i, roundKey);
printState(state);
aes_cipher(state, roundKey); // includes printState calls inside if in debug mode
}
// Final round (no MixColumns)
printState(state);
createRoundKey(expandedKey + 16 * nbrRounds, roundKey);
subBytes(state);
printState(state);
shiftRows(state);
printState(state);
addRoundKey(state, roundKey);
printState(state);
}
char aes_encrypt(unsigned char *input, unsigned char *output,
unsigned char *key, enum keySize size) {
int nbrRounds;
int expandedKeySize;
unsigned char block[16];
unsigned char *expandedKey = NULL;
// Determine number of rounds based on key size
switch (size) {
case SIZE_16: nbrRounds = 10; break;
case SIZE_24: nbrRounds = 12; break;
case SIZE_32: nbrRounds = 14; break;
default: return ERROR_AES_UNKNOWN_KEYSIZE;
}
expandedKeySize = 16 * (nbrRounds + 1);
expandedKey = (unsigned char *)malloc(expandedKeySize);
if (expandedKey == NULL) {
return ERROR_MEMORY_ALLOCATION_FAILED;
}
// Map input (row-major to column-major for AES)
for (int row = 0; row < 4; row++) {
for (int col = 0; col < 4; col++) {
block[row + 4 * col] = input[4 * row + col];
}
}
// Expand the key
KeyExpansion(expandedKey, key, size, expandedKeySize);
// Encrypt the block
aes_main(block, expandedKey, nbrRounds);
// Map block back to output (column-major to row-major)
for (int row = 0; row < 4; row++) {
for (int col = 0; col < 4; col++) {
output[4 * row + col] = block[row + 4 * col];
}
}
// de-allocate memory for expandedKey
free(expandedKey);
return SUCCESS;
}
void invSubBytes(unsigned char *state) {
for (int i = 0; i < 16; i++) {
state[i] = getSBoxInvert(state[i]);
}
}
void invShiftRows(unsigned char *state) {
for (int row = 0; row < 4; row++) {
invShiftRow(state + row * 4, row);
}
}
void invShiftRow(unsigned char *state, unsigned char nbr) {
unsigned char temp[4];
// Perform rotation to the right by `nbr` positions
for (int i = 0; i < 4; i++) {
temp[i] = state[(i - nbr + 4) % 4];
}
// Copy back the rotated values
for (int i = 0; i < 4; i++) {
state[i] = temp[i];
}
}
void invMixColumns(unsigned char *state) {
unsigned char column[4];
for (int col = 0; col < 4; col++) {
// Extract one column (4 bytes from each row)
for (int row = 0; row < 4; row++) {
column[row] = state[row * 4 + col];
}
// Apply inverse MixColumn transformation
invMixColumn(column);
// Store transformed column back into the state
for (int row = 0; row < 4; row++) {
state[row * 4 + col] = column[row];
}
}
}
void invMixColumn(unsigned char *column) {
unsigned char a[4];
for (int i = 0; i < 4; i++)
a[i] = column[i];
unsigned char a0_14 = gfmul(a[0], 14);
unsigned char a1_11 = gfmul(a[1], 11);
unsigned char a2_13 = gfmul(a[2], 13);
unsigned char a3_9 = gfmul(a[3], 9);
unsigned char a0_9 = gfmul(a[0], 9);
unsigned char a1_14 = gfmul(a[1], 14);
unsigned char a2_11 = gfmul(a[2], 11);
unsigned char a3_13 = gfmul(a[3], 13);
unsigned char a0_13 = gfmul(a[0], 13);
unsigned char a1_9 = gfmul(a[1], 9);
unsigned char a2_14 = gfmul(a[2], 14);
unsigned char a3_11 = gfmul(a[3], 11);
unsigned char a0_11 = gfmul(a[0], 11);
unsigned char a1_13 = gfmul(a[1], 13);
unsigned char a2_9 = gfmul(a[2], 9);
unsigned char a3_14 = gfmul(a[3], 14);
column[0] = a0_14 ^ a1_11 ^ a2_13 ^ a3_9;
column[1] = a0_9 ^ a1_14 ^ a2_11 ^ a3_13;
column[2] = a0_13 ^ a1_9 ^ a2_14 ^ a3_11;
column[3] = a0_11 ^ a1_13 ^ a2_9 ^ a3_14;
}
void aes_invRound(unsigned char *state, unsigned char *roundKey) {
invShiftRows(state);
invSubBytes(state);
addRoundKey(state, roundKey);
invMixColumns(state);
}
void aes_invCipher(unsigned char *state, unsigned char *expandedKey, int nbrRounds) {
unsigned char roundKey[16];
// Initial round key for final round
createRoundKey(expandedKey + 16 * nbrRounds, roundKey);
addRoundKey(state, roundKey);
// Inverse rounds (excluding final round)
for (int round = nbrRounds - 1; round > 0; round--) {
createRoundKey(expandedKey + 16 * round, roundKey);
aes_invRound(state, roundKey);
}
// Final inverse round (no invMixColumns)
createRoundKey(expandedKey, roundKey);
invShiftRows(state);
invSubBytes(state);
addRoundKey(state, roundKey);
}
char aes_decrypt(unsigned char *input, unsigned char *output,
unsigned char *key, enum keySize size) {
int nbrRounds;
int expandedKeySize;
unsigned char block[16];
unsigned char *expandedKey = NULL;
// Determine the number of rounds based on key size
switch (size) {
case SIZE_16: nbrRounds = 10; break;
case SIZE_24: nbrRounds = 12; break;
case SIZE_32: nbrRounds = 14; break;
default: return ERROR_AES_UNKNOWN_KEYSIZE;
}
expandedKeySize = 16 * (nbrRounds + 1);
expandedKey = (unsigned char *)malloc(expandedKeySize);
if (expandedKey == NULL) {
return ERROR_MEMORY_ALLOCATION_FAILED;
}
// Transpose input (column-major block for AES)
for (int row = 0; row < 4; row++) {
for (int col = 0; col < 4; col++) {
block[row + 4 * col] = input[4 * row + col];
}
}
// Key expansion
KeyExpansion(expandedKey, key, size, expandedKeySize);
// Decrypt
aes_invCipher(block, expandedKey, nbrRounds);
// Transpose back into output (row-major)
for (int row = 0; row < 4; row++) {
for (int col = 0; col < 4; col++) {
output[4 * row + col] = block[row + 4 * col];
}
}
// de-allocate memory for expandedKey
free(expandedKey);
return SUCCESS;
}
int main(int argc, char *argv[]) {
// Rounds: Number of AES rounds
// Words/Key: Number of 32-bit words per round key (Nb = 4 for AES)
// Round Keys: Total words in expanded key = Nb × (Rounds + 1)
// KeyExp (B): Key expansion size in bytes = Round Keys × 4
// Block (B): Block size in bytes = 128 bits / 8 = 16
//+-----------+ Block Size | Rounds | Words/Key | Round Keys | KeyExp (B) | Block (B) |
//|-----------|------------|--------|-----------|------------|------------|-----------|
//| AES-128 | 128 bits | 10 | 4 | 44 | 176 | 16 |
//| AES-192 | 128 bits | 12 | 4 | 52 | 208 | 16 |
//| AES-256 | 128 bits | 14 | 4 | 60 | 240 | 16 |
//+-----------+------------+--------+-----------+------------+------------+-----------+
// the expanded keySize to store full set of round keys
int expandedKeySize = 240;
unsigned char expandedKey[expandedKeySize];
// the cipher key (FIPS 197 example (page 28) 128-bit Cipher Key in Appendix A)
//unsigned char key[16] = {0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
// 0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c};
// (FIPS 197 example (page 34) in Appendix B)
// AES uses an internal structure called the state, which is a 4x4 byte matrix (16 bytes total).
// AES operates on 128-bit blocks (16 bytes), always — regardless of key size (128, 192, 256).
//unsigned char plaintext[16] = {0x32, 0x43, 0xf6, 0xa8, 0x88, 0x5a, 0x30, 0x8d,
// 0x31, 0x31, 0x98, 0xa2, 0xe0, 0x37, 0x07, 0x34};
// the cipher key size defined on Line 86
enum keySize size = SIZE_32;
// These examples are in Appendix C of FIPS 197 starting on page 35 (2001 version)
// AES 128-bit key and plaintext input
unsigned char key[16] = {
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
};
unsigned char plaintext[16] = {
0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff
};
// AES-192 key and plaintext input
unsigned char key192[24] = {
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17
};
unsigned char plaintext192[16] = {
0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff
};
// AES-256 key and plaintext input
unsigned char key256[32] = {
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
};
unsigned char plaintext256[16] = {
0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff
};
// the ciphertext
unsigned char ciphertext[16];
// the decrypted text
unsigned char decryptedtext[16];
int i;
printf("Implementation of the AES algorithm in C\n");
printf("\nCipher Key (hex format):\n");
for (i = 0; i < 16; i++) {
// Print characters in hex format, 16 chars per line
printf("%2.2x%c", key[i], ((i + 1) % 16) ? ' ' : '\n');
}
// Test the Key Expansion
KeyExpansion(expandedKey, key, size, expandedKeySize);
printf("\nExpanded Key (hex format):\n");
for (i = 0; i < expandedKeySize; i++) {
printf("%2.2x%c", expandedKey[i], ((i + 1) % 16) ? ' ' : '\n');
}
printf("\nPlaintext (hex format):\n");
for (i = 0; i < 16; i++) {
printf("%2.2x%c", plaintext[i], ((i + 1) % 16) ? ' ' : '\n');
}
// AES Encryption
aes_encrypt(plaintext, ciphertext, key, SIZE_32);
printf("\nCiphertext (hex format):\n");
for (i = 0; i < 16; i++) {
printf("%02x%c", ciphertext[i], ((i + 1) % 16) ? ' ' : '\n');
}
// AES Decryption
aes_decrypt(ciphertext, decryptedtext, key, SIZE_32);
printf("\nDecrypted text (hex format):\n");
for (i = 0; i < 16; i++) {
printf("%2.2x%c", decryptedtext[i], ((i + 1) % 16) ? ' ' : '\n');
}
return 0;
}