From: Tyler Yip - UnixWeenie(tm) <davros@ecst.csuchico.edu>
Date: Sat, 19 Jun 93 00:28:31 PDT
To: cypherpunks@toad.com
Subject: The Computer Shopper cipher
Message-ID: <9306190728.AA09090@hairball.ecst.csuchico.edu>
MIME-Version: 1.0
Content-Type: text/plain


Compared to the lines of the Computer Shopper program, how would this variant 
evaluate out time-complexity wise?  I'm not sure how sophisticated the
attacks on pseudo-random generators are.
This one includes an random generator shift, based upon the random numbers.

-----------------------------------------------------------------------------
#include	<stdio.h>

static int seed;

int rand1(int seedval) { return (seed * 183041 % 183319 + 1); }

int rand2(int seed) { return (seed * 502001 % 502441 + 1); }

void main(int argc, char *argv[]) {

	int	current;
	FILE *input, *output;

	if (argc !=3) {
		fprintf(stderr, "Usage: %s input output\n", argv[0]);
		exit(1);
	}
	if ((input = fopen(argv[1], "rb")) == NULL) {
		fprintf(stderr, "Error opening inputfile %s\n",argv[1]);
	}
	if ((output = fopen(argv[2], "wb")) == NULL) {
		fprintf(stderr, "Error opening outputfile %s\n",argv[1]);
	}

	printf("Enter cipher key: ");
	seed = getc(stdin);
	current = fgetc(input);
	while(!feof(input)) {
		fputc(current ^ seed, output);
		current = fgetc(input);
		if (seed && 8) {
			seed = rand1(seed);
		}
		else {
			seed = rand2(seed);
		}
	}
	fclose(input);
	fclose(output);
}
-- 
Tyler Yip, UnixWeenie(tm)        \ God put me on Earth to accomplish a certain
email: davros@ecst.csuchico.edu   \ number of things.  Right now I am so far 
California State University, Chico \ behind I will never die. -Calvin & Hobbes