Solution for Catch Me challenge in ASIS CTF 2016 Quals

catch.c

#include <stdio.h>

int is_valid(unsigned char c) {
    return c == 0 || c == 45 || c >= 48 && c <= 57 || c >= 65 && c <= 90 || c == 95 || c >= 97 && c <= 122;
}

int main () {
    unsigned char h1[17] = {0x87, 0x29, 0x34, 0xC5, 0x55, 0xB0, 0xC2, 0x2D, 0xEE, 0x60, 0x34, 0xD4, 0x55, 0xEE, 0x80, 0x7C, 0};
    unsigned char h2[17] = {0xEE, 0x2F, 0x37, 0x96, 0x3D, 0xEB, 0x9C, 0x79, 0xEE, 0x2C, 0x33, 0x95, 0x78, 0xED, 0xC1, 0x2B, 0};
    
    unsigned char bytes[8] = {0xb1, 0x19, 0x4, 0xa1, 0, 0, 0, 0};
    for (int a = 0; a < 256; a++) {
        for (int b = 0; b < 256; b++) {
            for (int c = 0; c < 256; c++) {
                for (int d = 0; d < 256; d++) {
                    bytes[4] = a;
                    bytes[5] = b;
                    bytes[6] = c;
                    bytes[7] = d;
                    for (int j = 0; j < 16; j++) {
                        h1[j] ^= bytes[j & 7];
                    }
                    for (int j = 0; j < 16; j++) {
                        h2[j] ^= bytes[j & 7];
                    }
                    int sum = 0;
                    for (int j = 0; j < 16; j++) {
                        sum += h1[j];
                        sum += h2[j];
                    }
                    if (sum == 2388) {
                        int ok = 1;
                        for (int j = 0; j < 16; j++) {
                            if (!is_valid(h1[j]) || !is_valid(h2[j])) {
                                ok = 0; break;
                            }
                        }
                        if (ok) {
                            printf("%s%s\n", h1, h2);
                        }
                    }
                }
            }
        }
    }
}