pseudo random: THE CODE

[maruishi@netcom.com]

On Sun, 18 Feb 1996, Bruce Murphy wrote:

> In message <199602172002.MAA09152@netcom20.netcom.com>, 
>   maruishi@netcom.com wrote:
> > 
> > I was trying to think of a way to come up with true random numbers...
> > And knowing a bit of UNIX socket TCP/IP programming I made a small little
> > program that generates random numbers by measuring the mili-second timing ies
> >  a TCP packet to bounce back, from another network. 
> >   My program simply send some data to port 7 (echo port) of a network on an i
> > nternal list. Then timing it, randomly picks a different network to send to. 
> 
> Interesting idea. Trends may be externally visible, You would probably
> want to normalize it, and you would find that there was quite a few
> deterministic elements of network load -> delay.
> 
> Oh, did I mention clock granularity?
> 
> In short you really aren't going to get 'random numbers' from such a
> scheme, but that's not to say you couldn't have fun playing with it,
> you might even find some use for the ways of calculating immediate
> network load around a node. Especially with regard to interception of
> packets and allowing for time discrepancies whilst doing so.
> 
> Altogether off topic, but could maybe be developed into an idea with,
> maybe a 30% change of being Perrygrammed. Keep working.
> 
> <invisible to perry>
> Bounce me the code, could be interesting
> </invisible to perry>
> 
> --
> Packrat (BSc/BE;COSO;Wombat Admin)
> Nihil illegitemi carborvndvm.
> 
Here is the code. Its pretty quick and dirty.

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <time.h>
#include <netdb.h>
#include <unistd.h>
#include <sys/time.h>
#include <time.h>

#define NET_NUM 1/*change this to the number of networks in
				the list below******************************/
struct timezone tz;
struct sockaddr_in addr;
unsigned int bits;

main(int argc, char **argv)
{
struct timeval tv;
register FILE *fin, *key, *nets;
int sock, c, dt, i, net;
unsigned char *packet;
unsigned char ch;

if(argc != 3)
{
printf("Usage: %s [key.file.path] [number of bits in key]\n", argv[0]);
exit(1);
} 
		if((key = fopen(argv[1], "wb")) == NULL)
		{
			perror("file open");
			exit(1);
		}
net = 1;
packet = (unsigned char *)malloc(16);/*you can of course change this value*/
memset(packet, "X", 16);
bits = atoi(argv[2]);
bits = bits / 8; /*how many bytes?*/
	for(i = 0; i<bits; i++)
	{
		sock = con(getn(net));/*Make a connection and return the 
socket.*/
		if((fin = fdopen(sock, "r")) == NULL)
		{
			perror("fdopen");
			close(sock);
			exit(1);
		}
		(void) gettimeofday(&tv, &tz);
sendto(sock,packet, 16, 0, (struct sockaddr *) &addr,sizeof(struct 
sockaddr));
		write(sock, "\r\n", 2);
		while ((c = getc(fin)) != '\n') ;
		dt = deltaT(&tv);
		close(sock);
		fclose(fin);
		ch = dt % 255;
		fputc(ch, key);
		net = dt % NET_NUM;
	}/*for*/
}

int con(char *where)
{
struct sockaddr_in addr;
struct hostent *host_;
register FILE *fin, *fp;
int sock, c, dt;
char *packet;
unsigned char ch;

(void) bzero((char *)&addr, sizeof(struct sockaddr_in));
	addr.sin_addr.s_addr = inet_addr(where);
	if((int)addr.sin_addr.s_addr == -1)
	{
			host_ = gethostbyname(where);
		if (host_ != NULL)
			bcopy(host_->h_addr, (char *)&addr.sin_addr, 
host_->h_length);
		else
			{
			printf("Host not found.\n");
			exit(1);
			}
	}
	addr.sin_family = AF_INET;
	addr.sin_port = htons(7);
		
		sock = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
		if (sock < 0) {
			fprintf(stderr,"error: socket() failed\n");
			perror("socket");
			return;
		}
	if(connect(sock, (struct sockaddr*) &addr, sizeof(addr))<0)
	{
		close(sock);
		fprintf(stderr, "socket connection error\n");
		perror("connection");
		exit(1);
	}
	return sock;
}

/**************put your network list down here************/
char *getn(int num)
{
char *nets[] = 
	{
	"127.0.0.1"
	};
return nets[num];
}

/*This part is taken from traceroute.*/
deltaT(tp)
struct timeval *tp;
{
	struct timeval tv;

	(void) gettimeofday(&tv, &tz);
	tvsub(&tv, tp);
	return (tv.tv_sec*1000 + (tv.tv_usec + 500)/1000);
}

tvsub(out, in)
register struct timeval *out, *in;
{
	if ((out->tv_usec -= in->tv_usec) < 0)   {
		out->tv_sec--;
		out->tv_usec += 1000000;
	}
	out->tv_sec -= in->tv_sec;
}