Re: IPG algorithim

[Eric Murray <ericm@lne.com>]

Igor Chudov @ home writes:
> 
> [This is an addition to my previous reply to Eric]
> 
> It bugs me that you are using rand() (a fairly lame pseudo-random
> function that was never intended to be used in cryptographic
> applications) to seed A, B, C and JV and then test the A(JV) for
> randomness. Some may object to that.

Yea, you're right, rand() is lame.

I added /dev/random to my Linux box and changed my small test to use it.
I also changed the way that I use JV- I had been setting it to a random
value for each trip through the "engine", but since I beleive that
its value can't really be random (if you want to be able to have someone
decrypt your stuff :-) but must be exchanged in the key, I set it
to a random value once and then let it float.  It's also a lot faster
that way, /dev/random is pretty slow (because it's looking for real
random material).

My results from xnoisesph were wrong- xnoisesph wants random bytes
instead of random integers in ascii format as I was producing.
Changing it (as I have below) makes the xnoisesph output look
much better, but it still isn't all that random.  The random seed generators
I have written that get their randomness from repeated calls
to high-resolution timers and hashes of system log files do better.
I also fixed a minor bug in arg processing.






#include <stdio.h>
#include <fcntl.h>

/* a C translation of the IPG "EUREKA" algorithim's "engine".
** This is supposed to produce random numbers for the IPG
** "encryptor stream".
** See http://www.netprivacy.com/ for the original description.
** Eric Murray  ericm@lne.com  This code placed under GNU copyleft. 
** V0.2 */

typedef unsigned char byte;
typedef unsigned short uint16;


/* tables: */
uint16 A[53];
uint16 B[53];
uint16 C[53];


#ifndef NO_DEV_RANDOM
uint16 getrand()
{
	uint16 ret;
	int fd = open("/dev/random",O_RDONLY);
	if (fd <= 0) {
		perror("/dev/random"); exit(-1);
	}
	read(fd,(unsigned char *)(&ret),sizeof(ret));
	close(fd);
	return(ret);
}
#else
/* do something appropriate for your OS here, rand() is lame. */
#define getrand rand
#endif


int init_table(uint16*table, uint16 min, uint16 max)
{
	/* IPG specifies no algorithim for producing the "random"
	** initial values in the ABC tables, but it's obvious that
	** it requires a PRNG that's somehow seeded from the "key".
	** I've used /dev/random here, so there's no question that
	** I'm starting out with pretty good random values. */
	int i;
	int count, r;

	for(i = 0; i < 53; i++) {
		table[i] = min + (getrand() % (max - min));
	}
}

main(int argc, char **argv)
{
	uint16 jv;
	int argcnt, i, n, count, diehard, nelem;

	diehard = 0;
	argcnt = 1;
	if (argc >= 2) {
		if (strncmp(argv[argcnt],"-d",2) == 0) {
			diehard++;
			argcnt++;
		}
	}
	if (argc > argcnt - 1 ) {
		n = atoi(argv[argcnt]);
		fprintf(stderr,"Generating %d values\n",n);
	}
	else {
		n = 2000;
	}

	/* seed tables: */
	fprintf(stderr,"Seeding:  A");  fflush(stderr);
	init_table(A,0,65535);
	fprintf(stderr," B");  fflush(stderr);
	init_table(B,0,12227);
	fprintf(stderr," C");  fflush(stderr);
	init_table(C,16384,20361);
	fprintf(stderr,"\n");  fflush(stderr);

	/* generate n values: */
	/* jv is "random" (where's it seeded from?) */
	jv = (uint16)(getrand() % 53);
	for(; n > 0; n--) {

		/* count limits the number of traverses to 53^2 so we don't get stuck */
		/* 2809 is actually too low per Chudov:
		** "For example, if ALL B == 1, A == 16385, and C == 20361, the
		**  loop may need (20361-16385) passes to get to the < 16384 value."
		*/
		for(count = 0; count < 2809; count++) {
			jv++;
			if (jv == 53) jv = 0;
			A[jv] = (A[jv] + B[jv]) % C[jv];
			if (A[jv] < 16384) break;
		}
		if (count == 2809) fprintf(stderr,"Oops.\n");
		else {
			if (!diehard) {
				write(1,(unsigned char *)&A[jv],sizeof(uint16));
			}
			else {
				/* print output in DIEHARD required format:
				** actually since we have 16-bit ints and DIEHARD
				** wants 32-bit ints, we print 20 per line instead of 10 */
				if (nelem++ > 19) {printf("\n"); nelem = 0;}
				printf("%4.4x",(unsigned int)A[jv]);
			}
		}
	}
}
-- 
Eric Murray  ericm@lne.com  ericm@motorcycle.com  http://www.lne.com/ericm
PGP keyid:E03F65E5 fingerprint:50 B0 A2 4C 7D 86 FC 03  92 E8 AC E6 7E 27 29 AF