sjero.net Git - ltp2tcp/blob - checksums.c

   1 /******************************************************************************
   2 IPv4 and IPv6 Header Checksum Code
   3
   4 Copyright (C) 2013  Samuel Jero <sj323707@ohio.edu>
   5
   6 This program is free software: you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation, either version 3 of the License, or
   9 (at your option) any later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18
  19 Author: Samuel Jero <sj323707@ohio.edu>
  20 Date: 02/2013
  21 ******************************************************************************/
  22 #include <string.h>
  23 #include <arpa/inet.h>
  24 #include "checksums.h"
  25
  26 /*Stupid Solaris*/
  27 #ifndef u_int32_t
  28 #define u_int32_t uint32_t
  29 #endif
  30 #ifndef u_int16_t
  31 #define u_int16_t uint16_t
  32 #endif
  33
  34 //Pseudo Headers for checksums
  35 struct ip6_pseudo_hdr{
  36         u_char          src[IP6_ADDR_LEN];
  37         u_char          dest[IP6_ADDR_LEN];
  38         unsigned int len;
  39         u_char          zero[3];
  40         u_char          nxt;
  41 };
  42 struct ip4_pseudo_hdr{
  43         u_char          src[IP4_ADDR_LEN];
  44         u_char          dest[IP4_ADDR_LEN];
  45         unsigned int len;
  46         u_char          zero[3];
  47         u_char          nxt;
  48 };
  49
  50 /*From http://gitorious.org/freebsd/freebsd/blobs/HEAD/sbin/dhclient/packet.c
  51  * under GNU GPL*/
  52 u_int32_t checksum(u_char *buf, unsigned nbytes, u_int32_t sum)
  53 {
  54         int i;
  55         /* Checksum all the pairs of bytes first... */
  56         for (i = 0; i < (nbytes & ~1U); i += 2) {
  57                 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
  58                 if (sum > 0xFFFF)
  59                         sum -= 0xFFFF;
  60         }
  61         /*
  62          * If there's a single byte left over, checksum it, too.
  63          * Network byte order is big-endian, so the remaining byte is
  64          * the high byte.
  65          */
  66         if (i < nbytes) {
  67                 sum += buf[i] << 8;
  68                 if (sum > 0xFFFF)
  69                         sum -= 0xFFFF;
  70         }
  71         return (sum);
  72 }
  73
  74 /*From http://gitorious.org/freebsd/freebsd/blobs/HEAD/sbin/dhclient/packet.c
  75  * under GNU GPL*/
  76 u_int32_t wrapsum(u_int32_t sum)
  77 {
  78         sum = ~sum & 0xFFFF;
  79         return (htons(sum));
  80 }
  81
  82 u_int16_t ipv6_pseudohdr_chksum(u_char* buff, int len, u_char* dest, u_char* src, int type){
  83         struct ip6_pseudo_hdr hdr;
  84
  85         //create pseudo header
  86         memset(&hdr, 0, sizeof(struct ip6_pseudo_hdr));
  87         memcpy(hdr.src, src, IP6_ADDR_LEN);
  88         memcpy(hdr.dest, dest, IP6_ADDR_LEN);
  89         hdr.nxt=type;
  90         hdr.len=htonl(len);
  91
  92         //calculate total checksum
  93         return wrapsum(checksum((unsigned char*)&hdr,sizeof(struct ip6_pseudo_hdr),checksum(buff,len,0)));
  94 }
  95
  96 u_int16_t ipv4_pseudohdr_chksum(u_char* buff, int len, u_char* dest, u_char* src, int type){
  97         struct ip4_pseudo_hdr hdr;
  98
  99         //create pseudo header
 100         memset(&hdr, 0, sizeof(struct ip4_pseudo_hdr));
 101         memcpy(hdr.src, src, IP4_ADDR_LEN);
 102         memcpy(hdr.dest, dest, IP4_ADDR_LEN);
 103         hdr.nxt=type;
 104         hdr.len=htonl(len);
 105
 106         //calculate total checksum
 107         return wrapsum(checksum((u_char*)&hdr,sizeof(struct ip4_pseudo_hdr),checksum(buff,len,0)));
 108 }
 109
 110 u_int16_t ipv4_chksum(u_char* buff, int len){
 111         return wrapsum(checksum(buff,len,0));
 112 }