#include <stdio.h>
#include <stdint.h>
#include <string.h>

#define BLOCK_SIZE 16

static uint8_t compute_xor_checksum(const uint8_t *block, size_t n) {
    uint8_t cs = 0;
    for (size_t i = 0; i < n; ++i) {
        cs ^= block[i];
    }
    return cs;
}

int main(void) {
    uint8_t block[BLOCK_SIZE];
    const char *msg = "Hello OSTEP!";
    memset(block, 0, BLOCK_SIZE);
    strncpy((char *)block, msg, BLOCK_SIZE - 1);
    uint8_t stored_cs = compute_xor_checksum(block, BLOCK_SIZE);
    printf("Stored data: %s\n", (char *)block);
    printf("Stored checksum: 0x%02X\n", stored_cs);
    block[3] ^= 0x01;  /* silent corruption */
    uint8_t read_cs = compute_xor_checksum(block, BLOCK_SIZE);
    printf("Read checksum: 0x%02X\n", read_cs);
    if (read_cs != stored_cs) {
        printf("Corruption detected! Data integrity violated.\n");
    } else {
        printf("Checksums match.\n");
    }
    return 0;
}