Checksum Computation!!

[ltp2tcp] / checksums.c

diff --git a/checksums.c b/checksums.c
new file mode 100644 (file)
index 0000000..ab29590
--- /dev/null
+++ b/checksums.c
@@ -0,0 +1,112 @@
+/******************************************************************************
+IPv4 and IPv6 Header Checksum Code
+
+Copyright (C) 2013  Samuel Jero <sj323707@ohio.edu>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Author: Samuel Jero <sj323707@ohio.edu>
+Date: 02/2013
+******************************************************************************/
+#include <string.h>
+#include <arpa/inet.h>
+#include "checksums.h"
+
+/*Stupid Solaris*/
+#ifndef u_int32_t
+#define u_int32_t uint32_t
+#endif
+#ifndef u_int16_t
+#define u_int16_t uint16_t
+#endif
+
+//Pseudo Headers for checksums
+struct ip6_pseudo_hdr{
+       u_char          src[IP6_ADDR_LEN];
+       u_char          dest[IP6_ADDR_LEN];
+       unsigned int len;
+       u_char          zero[3];
+       u_char          nxt;
+};
+struct ip4_pseudo_hdr{
+       u_char          src[IP4_ADDR_LEN];
+       u_char          dest[IP4_ADDR_LEN];
+       unsigned int len;
+       u_char          zero[3];
+       u_char          nxt;
+};
+
+/*From http://gitorious.org/freebsd/freebsd/blobs/HEAD/sbin/dhclient/packet.c
+ * under GNU GPL*/
+u_int32_t checksum(u_char *buf, unsigned nbytes, u_int32_t sum)
+{
+       int i;
+       /* Checksum all the pairs of bytes first... */
+       for (i = 0; i < (nbytes & ~1U); i += 2) {
+               sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
+               if (sum > 0xFFFF)
+                       sum -= 0xFFFF;
+       }
+       /*
+        * If there's a single byte left over, checksum it, too.
+        * Network byte order is big-endian, so the remaining byte is
+        * the high byte.
+        */
+       if (i < nbytes) {
+               sum += buf[i] << 8;
+               if (sum > 0xFFFF)
+                       sum -= 0xFFFF;
+       }
+       return (sum);
+}
+
+/*From http://gitorious.org/freebsd/freebsd/blobs/HEAD/sbin/dhclient/packet.c
+ * under GNU GPL*/
+u_int32_t wrapsum(u_int32_t sum)
+{
+       sum = ~sum & 0xFFFF;
+       return (htons(sum));
+}
+
+u_int16_t ipv6_pseudohdr_chksum(u_char* buff, int len, u_char* dest, u_char* src, int type){
+       struct ip6_pseudo_hdr hdr;
+
+       //create pseudo header
+       memset(&hdr, 0, sizeof(struct ip6_pseudo_hdr));
+       memcpy(hdr.src, src, IP6_ADDR_LEN);
+       memcpy(hdr.dest, dest, IP6_ADDR_LEN);
+       hdr.nxt=type;
+       hdr.len=htonl(len);
+
+       //calculate total checksum
+       return wrapsum(checksum((unsigned char*)&hdr,sizeof(struct ip6_pseudo_hdr),checksum(buff,len,0)));
+}
+
+u_int16_t ipv4_pseudohdr_chksum(u_char* buff, int len, u_char* dest, u_char* src, int type){
+       struct ip4_pseudo_hdr hdr;
+
+       //create pseudo header
+       memset(&hdr, 0, sizeof(struct ip4_pseudo_hdr));
+       memcpy(hdr.src, src, IP4_ADDR_LEN);
+       memcpy(hdr.dest, dest, IP4_ADDR_LEN);
+       hdr.nxt=type;
+       hdr.len=htonl(len);
+
+       //calculate total checksum
+       return wrapsum(checksum((u_char*)&hdr,sizeof(struct ip4_pseudo_hdr),checksum(buff,len,0)));
+}
+
+u_int16_t ipv4_chksum(u_char* buff, int len){
+       return wrapsum(checksum(buff,len,0));
+}