Question

Write a C program that can transparently authenticate all IP packets from/to specified IP address with given key.

program.c such that program (e.g., program 192.124.5.5 secret) will intercept packets

• for any outgoing packet to the specified , transparently change the original payload X (the bytes after the IP header) by concatenating the original payload X with 16 bytes of md5(X|key), and adjust the IP header accordingly (e.g., increase the packet total length, re-calculate the checksum) so that the outgoing packet will have payloadX|md5(X|key)to

• for any incoming packet from specified , check the packet payload for the md5 authentication with the given . Specifically, divide the packet payload (those bytes after the IP header) as two parts X, Y where Y is the last 16 bytes of the packet payload and X is the rest. If ( md5(X|key) == Y), change the payload of the incoming packet from X|Y to X, and adjust the IP header accordingly (e.g., decrease the packet total length, re-calculate the checksum) so that the incoming packet will be restored to its original form without keyed md5 authentication before sent to the receiving process. Otherwise, print out error message of failed authentication and drop the incoming packet.

Once you have developed such program, you need to run two instances of VM1 &  VM2  and to  make  VM1 &  VM2  have two  different  IP addresses  (e.g.,  ip1, ip2). They should be able to ping to each other. On VM1, set up appropriate ipfw rules to divert incoming/outgoing  traffic from/to   VM2   to <divert   port>.  Similarly,  on   VM2,   set  up appropriate ipfw rules to divert incoming/outgoing traffic from/to VM1 to <divert port>

Please include output of the code of experiments:

a) At VM1, run ./program secretKey

At VM2, run./ip_authAll secretKey

ping from VM1 to VM2
ping from VM2 to VM1

Answer 1

C Program to display hostname and IP address

There are many ways to find Hostname and IP address of a local machine. Here is a simple method to find hostname and IP address using C program.

We will be using the following functions :-

gethostname() : The gethostname function retrieves the standard host name for the local computer.

gethostbyname() : The gethostbyname function retrieves host information corresponding to a host name from a host database.

inet_ntoa() : The inet_ntoa function converts an (Ipv4) Internet network address into an ASCII string in Internet standard dotted-decimal format.

// C program to display hostname
// and IP address
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

// Returns hostname for the local computer
void checkHostName(int hostname)
{
   if (hostname == -1)
   {
       perror("gethostname");
       exit(1);
   }
}

// Returns host information corresponding to host name
void checkHostEntry(struct hostent * hostentry)
{
   if (hostentry == NULL)
   {
       perror("gethostbyname");
       exit(1);
   }
}

// Converts space-delimited IPv4 addresses
// to dotted-decimal format
void checkIPbuffer(char *IPbuffer)
{
   if (NULL == IPbuffer)
   {
       perror("inet_ntoa");
       exit(1);
   }
}

// Driver code
int main()
{
   char hostbuffer[256];
   char *IPbuffer;
   struct hostent *host_entry;
   int hostname;

   // To retrieve hostname
   hostname = gethostname(hostbuffer, sizeof(hostbuffer));
   checkHostName(hostname);

   // To retrieve host information
   host_entry = gethostbyname(hostbuffer);
   checkHostEntry(host_entry);

   // To convert an Internet network
   // address into ASCII string
   IPbuffer = inet_ntoa(*((struct in_addr*)
                       host_entry->h_addr_list[0]));

   printf("Hostname: %s\n", hostbuffer);
   printf("Host IP: %s", IPbuffer);

   return 0;
}