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

   1 /******************************************************************************
   2 Author: Samuel Jero <sj323707@ohio.edu>
   3
   4 Date: 10/2012
   5
   6 Description: IPv4 and IPv6 Checksum code
   7 ******************************************************************************/
   8 #include <string.h>
   9 #include <arpa/inet.h>
  10 #include "checksums.h"
  11
  12 //Pseudo Headers for checksums
  13 struct ip6_pseudo_hdr{
  14         unsigned char src[IP6_ADDR_LEN];
  15         unsigned char dest[IP6_ADDR_LEN];
  16         unsigned int len;
  17         unsigned char zero[3];
  18         unsigned char nxt;
  19 };
  20 struct ip4_pseudo_hdr{
  21         unsigned char src[IP4_ADDR_LEN];
  22         unsigned char dest[IP4_ADDR_LEN];
  23         unsigned int len;
  24         unsigned char zero[3];
  25         unsigned char nxt;
  26 };
  27
  28 /*From http://gitorious.org/freebsd/freebsd/blobs/HEAD/sbin/dhclient/packet.c
  29  * under GNU GPL*/
  30 u_int32_t checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
  31 {
  32         int i;
  33         /* Checksum all the pairs of bytes first... */
  34         for (i = 0; i < (nbytes & ~1U); i += 2) {
  35                 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
  36                 if (sum > 0xFFFF)
  37                         sum -= 0xFFFF;
  38         }
  39         /*
  40          * If there's a single byte left over, checksum it, too.
  41          * Network byte order is big-endian, so the remaining byte is
  42          * the high byte.
  43          */
  44         if (i < nbytes) {
  45                 sum += buf[i] << 8;
  46                 if (sum > 0xFFFF)
  47                         sum -= 0xFFFF;
  48         }
  49         return (sum);
  50 }
  51
  52 /*From http://gitorious.org/freebsd/freebsd/blobs/HEAD/sbin/dhclient/packet.c
  53  * under GNU GPL*/
  54 u_int32_t wrapsum(u_int32_t sum)
  55 {
  56         sum = ~sum & 0xFFFF;
  57         return (htons(sum));
  58 }
  59
  60 u_int16_t ipv6_pseudohdr_chksum(unsigned char* buff, int len, unsigned char* dest, unsigned char* src, int type){
  61         struct ip6_pseudo_hdr hdr;
  62
  63         //create pseudo header
  64         memset(&hdr, 0, sizeof(struct ip6_pseudo_hdr));
  65         memcpy(hdr.src, src, IP6_ADDR_LEN);
  66         memcpy(hdr.dest, dest, IP6_ADDR_LEN);
  67         hdr.nxt=type;
  68         hdr.len=htonl(len);
  69
  70         //calculate total checksum
  71         return wrapsum(checksum((unsigned char*)&hdr,sizeof(struct ip6_pseudo_hdr),checksum(buff,len,0)));
  72 }
  73
  74 u_int16_t ipv4_pseudohdr_chksum(unsigned char* buff, int len, unsigned char* dest, unsigned char* src, int type){
  75         struct ip4_pseudo_hdr hdr;
  76
  77         //create pseudo header
  78         memset(&hdr, 0, sizeof(struct ip4_pseudo_hdr));
  79         memcpy(hdr.src, src, IP4_ADDR_LEN);
  80         memcpy(hdr.dest, dest, IP4_ADDR_LEN);
  81         hdr.nxt=type;
  82         hdr.len=htonl(len);
  83
  84         //calculate total checksum
  85         return wrapsum(checksum((unsigned char*)&hdr,sizeof(struct ip4_pseudo_hdr),checksum(buff,len,0)));
  86 }
  87
  88 u_int16_t ipv4_chksum(unsigned char* buff, int len){
  89         return wrapsum(checksum(buff,len,0));
  90 }