channel/c-write/lib/aes.c

#include "aes_internal.h"
#include "array.h"

uint8_t S_BOX[256] = {
    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,
};

uint8_t INV_S_BOX[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,
};

uint8_t ROUND_CONSTANT[32] = {
    0x00, 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,
};

size_t aes__block_get(size_t x, size_t y) {
    return x * 4 + y;
}

uint8_t aes__xtime(uint8_t x) {
    if ((x & 0x80) > 0) {
        return (uint8_t) ((x << 1) ^ 0x1B) & 0xFF;
    } else {
        return (uint8_t) (x << 1) & 0xFF;
    }
}

void aes__shift_rows(uint8_t* block, aes_encryption_mode_t mode) {
    uint8_t* word_original = malloc(sizeof(uint8_t) * WORD_LENGTH);

    for (size_t word_n = 1; word_n < WORD_LENGTH; word_n++) {
        size_t word_start_idx = word_n * WORD_LENGTH;

        for (size_t word_idx = 0; word_idx < WORD_LENGTH; word_idx++) {
            word_original[word_idx] = block[word_start_idx + word_idx];
        }

        for (size_t word_idx = 0; word_idx < WORD_LENGTH; word_idx++) {
            if (mode == encryption) {
                block[word_start_idx + word_idx] = word_original[(word_idx + word_n) % WORD_LENGTH];
            } else {
                block[word_start_idx + word_idx] = word_original[(word_idx - word_n) % WORD_LENGTH];
            }
        }
    }

    free(word_original);
}

void aes__mix_words(uint8_t* block, aes_encryption_mode_t mode) {
    if (mode == decryption) {
        for (size_t idx = 0; idx < WORD_LENGTH; idx++) {
            size_t start_idx = aes__block_get(idx, 0);

            uint8_t a = aes__xtime(aes__xtime(block[start_idx] ^ block[start_idx + 2]));
            uint8_t b = aes__xtime(aes__xtime(block[start_idx + 1] ^ block[start_idx + 3]));

            block[start_idx + 0] ^= a;
            block[start_idx + 2] ^= a;

            block[start_idx + 1] ^= b;
            block[start_idx + 3] ^= b;
        }
    }

    for (size_t idx = 0; idx < WORD_LENGTH; idx++) {
        size_t start_idx = aes__block_get(idx, 0);

        uint8_t xor = block[start_idx]
            ^ block[start_idx + 1]
            ^ block[start_idx + 2]
            ^ block[start_idx + 3];

        uint8_t first = block[start_idx];

        for (size_t i = 0; i < 3; i++) {
            block[start_idx + i] ^= aes__xtime(block[start_idx + i] ^ block[start_idx + i + 1]) ^ xor;
        }

        block[start_idx + 3] ^= aes__xtime(block[start_idx + 3] ^ first) ^ xor;
    }
}

void aes__add_round_key(uint8_t* block, uint8_t* round_key) {
    xor_arrays(block, round_key, BLOCK_LENGTH);
}

// NOTE: malloc
uint8_t* aes__expand_key(uint8_t* key) {
    // Original key + 10 round keys in an array
    size_t round_keys_array_size = (ROUNDS + 1) * BLOCK_LENGTH;
    uint8_t* round_keys = (uint8_t*) malloc(sizeof(uint8_t) * round_keys_array_size);
    size_t pos = 0;
    size_t round_constant_idx = 0;

    for (size_t idx = 0; idx < BLOCK_LENGTH; idx++) {
        round_keys[idx] = key[idx];
        pos += 1;
    }

    while (pos < round_keys_array_size) {
        for (size_t idx = 0; idx < WORD_LENGTH; idx++) {
            round_keys[idx + pos] = round_keys[idx + pos - WORD_LENGTH];
        }

        if (pos % BLOCK_LENGTH == 0) {
            uint8_t first = round_keys[pos];
            round_keys[pos] = round_keys[pos + 1];
            round_keys[pos + 1] = round_keys[pos + 2];
            round_keys[pos + 2] = round_keys[pos + 3];
            round_keys[pos + 3] = first;

            for (size_t idx = 0; idx < WORD_LENGTH; idx++) {
                uint8_t value = round_keys[pos + idx];
                round_keys[pos + idx] = S_BOX[value];
            }

            round_keys[pos] = round_keys[round_constant_idx];
            round_constant_idx += 1;
        }

        uint8_t* previous_word = &round_keys[pos];
        uint8_t* modifier_word = &round_keys[pos - BLOCK_LENGTH];
        xor_arrays(previous_word, modifier_word, WORD_LENGTH);
        pos += WORD_LENGTH;
    }

    return round_keys;
}

void aes__encrypt_block(uint8_t* block, uint8_t* round_keys) {
    aes__add_round_key(block, round_keys);
    for (size_t round = 1; round <= ROUNDS; round++) {
        for (size_t idx = 0; idx < BLOCK_LENGTH; idx++) {
            block[idx] = S_BOX[block[idx]];
        }

        aes__shift_rows(block, encryption);

        if (round != ROUNDS) {
            aes__mix_words(block, encryption);
        }

        aes__add_round_key(block, &round_keys[round * BLOCK_LENGTH]);
    }
}

void aes__decrypt_block(uint8_t* block, uint8_t* round_keys) {
    for (size_t round = ROUNDS; round >= 1; round--) {
        aes__add_round_key(block, &round_keys[round * BLOCK_LENGTH]);

        if (round != ROUNDS) {
            aes__mix_words(block, decryption);
        }

        aes__shift_rows(block, decryption);

        for (size_t idx = 0; idx < BLOCK_LENGTH; idx++) {
            block[idx] = INV_S_BOX[block[idx]];
        }
    }

    aes__add_round_key(block, round_keys);
}

BOOL aes__is_valid_padding(uint8_t* block) {
    uint8_t marker = block[BLOCK_LENGTH - 1];

    if (marker == 0) {
        return FALSE;
    }

    for (size_t idx = BLOCK_LENGTH - marker; idx < BLOCK_LENGTH; idx++) {
        if (block[idx] != marker) {
            return FALSE;
        }
    }

    return TRUE;
}

aes_padded_data_t aes_create_padded_data_container() {
    aes_padded_data_t out = {
        .data = NULL,
        .data_length = 0,
        .data_length_before_pad = 0,
        .padded_block = NULL,
        .length = 0,
    };

    return out;
}

// NOTE: Only drops padding, not the original data. Resets struct to defaults and returns the original data pointer.
uint8_t* aes_drop_padded_data_container(aes_padded_data_t* data) {
    uint8_t* ptr = data->data;
    free(data->padded_block);

    data->padded_block = NULL;
    data->data = NULL;
    data->data_length = 0;
    data->data_length_before_pad = 0;
    data->length = 0;

    return ptr;
}

// NOTE: malloc
int aes_pad_data(aes_padded_data_t* ptr, uint8_t* data, size_t length) {
    if (length == 0) {
        return 1;
    }

    uint8_t* padded_block_ptr = malloc(sizeof(uint8_t) * BLOCK_LENGTH);
    if (padded_block_ptr == NULL) {
        return 2;
    }

    ptr->data = data;
    ptr->data_length = length;
    ptr->padded_block = padded_block_ptr;

    if (length % BLOCK_LENGTH == 0) {
        // Fill with marker
        for (size_t idx = 0; idx < BLOCK_LENGTH; idx++) {
            padded_block_ptr[idx] = BLOCK_LENGTH;
        }

        ptr->data_length_before_pad = length;
    } else {
        size_t last_block_length = length % BLOCK_LENGTH;
        uint8_t* last_block = &data[length - last_block_length];
        size_t marker = BLOCK_LENGTH - last_block_length;

        // Fill with marker
        for (size_t idx = 0; idx < BLOCK_LENGTH; idx++) {
            padded_block_ptr[idx] = (uint8_t) (marker & 0xFF);
        }

        // Insert original data
        for (size_t idx = 0; idx < last_block_length; idx++) {
            padded_block_ptr[idx] = last_block[idx];
        }

        ptr->data_length_before_pad = length - last_block_length;
    }

    ptr->length = ptr->data_length_before_pad + BLOCK_LENGTH;

    return 0;
}

void aes_ecb(aes_encryption_mode_t mode, aes_padded_data_t* data, uint8_t* key) {
    uint8_t* round_keys = aes__expand_key(key);

    for (size_t idx = 0; idx < data->data_length_before_pad; idx += BLOCK_LENGTH) {
        if (mode == encryption) {
            aes__encrypt_block(&data->data[idx], round_keys);
        } else {
            aes__decrypt_block(&data->data[idx], round_keys);
        }
    }

    if (mode == encryption) {
        aes__encrypt_block(data->padded_block, round_keys);
    } else {
        aes__decrypt_block(data->padded_block, round_keys);
    }

    free(round_keys);
}

void aes_cbc(aes_encryption_mode_t mode, aes_padded_data_t* data, uint8_t* key) {
    uint8_t* round_keys = aes__expand_key(key);

    // TODO: Derive this properly
    uint8_t* previous_block = malloc(sizeof(uint8_t) * BLOCK_LENGTH * 2);
    for (size_t idx = 0; idx < BLOCK_LENGTH; idx++) {
        previous_block[idx] = 0;
    }

    for (size_t idx = 0; idx < data->data_length_before_pad; idx += BLOCK_LENGTH) {
        if (mode == encryption) {
            xor_arrays(&data->data[idx], previous_block, BLOCK_LENGTH);
            aes__encrypt_block(&data->data[idx], round_keys);
            clone_array(previous_block, &data->data[idx], BLOCK_LENGTH);
        } else {
            clone_array(&previous_block[BLOCK_LENGTH], &data->data[idx], BLOCK_LENGTH);
            aes__decrypt_block(&data->data[idx], round_keys);
            xor_arrays(&data->data[idx], previous_block, BLOCK_LENGTH);
            clone_array(previous_block, &previous_block[BLOCK_LENGTH], BLOCK_LENGTH);
        }
    }

    if (mode == encryption) {
        xor_arrays(data->padded_block, previous_block, BLOCK_LENGTH);
        aes__encrypt_block(data->padded_block, round_keys);
    } else {
        aes__decrypt_block(data->padded_block, round_keys);
        xor_arrays(data->padded_block, previous_block, BLOCK_LENGTH);
    }

    free(previous_block);
    free(round_keys);
}