Instead of waiting for it to download, Alex Lynch had the idea for us to generate it instead. We both coded IP address hashers, pitting his Ruby script against my C program. Naturally, the C code won.
The flag for this challenge is the checksum that is printed out after running this program.
# include <stdlib.h>
# include <stdio.h>
# include <string.h>
# include <openssl/md5.h>
int main (int argc, char **argv) {
MD5_CTX ctx;
MD5_Init(&ctx);
int i,j,k,l;
for (i=0; i < 256; i++) {
for (j=0; j < 256; j++) {
for (k=0; k < 256; k++) {
for (l=0; l < 256; l++) {
char addr[17];
if (i == 256 && i == j && j == k && k == l) {
snprintf(addr, 17, "%d.%d.%d.%d", i,j,k,l);
MD5_Update(&ctx, addr, strlen(addr));
}
else {
snprintf(addr, 17, "%d.%d.%d.%d\n", i,j,k,l);
MD5_Update(&ctx, addr, strlen(addr));
}
}
}
}
printf("Finished %d.0.0.0/8\n", i);
}
unsigned char digest[33];
MD5_Final(digest, &ctx);
char md5string[33];
for (i = 0; i < 16; ++i) {
sprintf(&md5string[i*2], "%02x", (unsigned int)digest[i]);
}
printf("%s\n", md5string);
return 0;
}