An elemental ircd decloaker

elemental_ircd_decloaker.c

/*

  Made by Adam Hose <adis@blad.is>
  Licensed under the GNU General Public License v2.0

  Most code is straight up copied from elemental ircd

 */
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

#define HOSTLEN 63
#define FNV1_32_INIT 0x811c9dc5UL
typedef uint32_t u_int32_t;


u_int32_t
fnv_hash(const unsigned char *s, int bits)
{
    u_int32_t h = FNV1_32_INIT;

    while (*s) {
        h ^= *s++;
        h += (h<<1) + (h<<4) + (h<<7) + (h << 8) + (h << 24);
    }
    if (bits < 32)
        h = ((h >> bits) ^ h) & ((1<<bits)-1);
    return h;
}


size_t
rb_strlcpy(char *dest, const char *src, size_t size)
{
    size_t ret = strlen(src);

    if(dest == src)
        return ret;

    if(size) {
        size_t len = (ret >= size) ? size - 1 : ret;
        memcpy(dest, src, len);
        dest[len] = '\0';
    }
    return ret;
}


static void
do_host_cloak_ip(const char *inbuf, char *outbuf)
{
    /* None of the characters in this table can be valid in an IP */
    char chartable[] = "ghijklmnopqrstuvwxyz";
    char *tptr;
    uint32_t accum = fnv_hash((const unsigned char*) inbuf, 32);
    int sepcount = 0;
    int totalcount = 0;

    rb_strlcpy(outbuf, inbuf, HOSTLEN + 1);

    for (tptr = outbuf; *tptr != '\0'; tptr++) {
        if (*tptr == '.') {
            sepcount++;
            continue;
        }

        if (sepcount < 2)
            continue;

        *tptr = chartable[(*tptr + accum) % 20];
        accum = (accum << 1) | (accum >> 31);
    }
}

int main(int argc, char *argv[]) {

  if (argc != 3) {
    printf("Elemental-IRCd ip decloaker\n");
    printf("Usage: <ip_prefix> <cloaked>\n");
    printf("Example: 139.59 139.59.xyz.xyz\n");
    return 1;
  }

  char *ip_prefix = argv[1];
  char *expected = argv[2];
  char *ip;
  char *mangledhost;

  for(int i = 0; i <= 255; i++) {
    for(int j = 0; j <= 255; j++) {
      mangledhost = malloc(HOSTLEN + 1);
      ip = malloc(HOSTLEN + 1);
      sprintf(ip, "%s.%i.%i", ip_prefix, i, j);

      do_host_cloak_ip(ip, mangledhost);

      if(strcmp(mangledhost, expected) == 0) {
        printf("Found: %s\n", ip);
        break;
      }

      free(mangledhost);
      free(ip);
    }
  }

  return 0;
}