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caesar.c revision 1.12 
      1 /*	$NetBSD: caesar.c,v 1.12 2003/08/07 09:37:07 agc Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1989, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Rick Adams.
      9  *
     10  * Authors:
     11  *	Stan King, John Eldridge, based on algorithm suggested by
     12  *	Bob Morris
     13  * 29-Sep-82
     14  *
     15  * Redistribution and use in source and binary forms, with or without
     16  * modification, are permitted provided that the following conditions
     17  * are met:
     18  * 1. Redistributions of source code must retain the above copyright
     19  *    notice, this list of conditions and the following disclaimer.
     20  * 2. Redistributions in binary form must reproduce the above copyright
     21  *    notice, this list of conditions and the following disclaimer in the
     22  *    documentation and/or other materials provided with the distribution.
     23  * 3. Neither the name of the University nor the names of its contributors
     24  *    may be used to endorse or promote products derived from this software
     25  *    without specific prior written permission.
     26  *
     27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     37  * SUCH DAMAGE.
     38  */
     39 
     40 #include <sys/cdefs.h>
     41 #ifndef lint
     42 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\n\
     43 	The Regents of the University of California.  All rights reserved.\n");
     44 #endif /* not lint */
     45 
     46 #ifndef lint
     47 #if 0
     48 static char sccsid[] = "@(#)caesar.c	8.1 (Berkeley) 5/31/93";
     49 #else
     50 __RCSID("$NetBSD: caesar.c,v 1.12 2003/08/07 09:37:07 agc Exp $");
     51 #endif
     52 #endif /* not lint */
     53 
     54 #include <ctype.h>
     55 #include <err.h>
     56 #include <errno.h>
     57 #include <math.h>
     58 #include <stdio.h>
     59 #include <string.h>
     60 #include <stdlib.h>
     61 #include <unistd.h>
     62 
     63 #define	LINELENGTH	2048
     64 #define	ROTATE(ch, perm) \
     65 	isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
     66 	    islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
     67 
     68 /*
     69  * letter frequencies (taken from some unix(tm) documentation)
     70  * (unix is a trademark of Bell Laboratories)
     71  */
     72 double stdf[26] = {
     73 	7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
     74 	0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
     75 	2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
     76 };
     77 
     78 
     79 int	main __P((int, char *[]));
     80 void	printit __P((const char *)) __attribute__((__noreturn__));
     81 
     82 int
     83 main(argc, argv)
     84 	int argc;
     85 	char **argv;
     86 {
     87 	int ch, dot, i, nread, winnerdot;
     88 	char *inbuf;
     89 	int obs[26], try, winner;
     90 
     91 	/* revoke setgid privileges */
     92 	setgid(getgid());
     93 
     94 	winnerdot = 0;
     95 	if (argc > 1)
     96 		printit(argv[1]);
     97 
     98 	if (!(inbuf = malloc(LINELENGTH)))
     99 		err(1, NULL);
    100 
    101 	/* adjust frequency table to weight low probs REAL low */
    102 	for (i = 0; i < 26; ++i)
    103 		stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
    104 
    105 	/* zero out observation table */
    106 	memset(obs, 0, 26 * sizeof(int));
    107 
    108 	if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
    109 		err(1, "reading from stdin");
    110 	for (i = nread; i--;) {
    111 		ch = inbuf[i];
    112 		if (islower(ch))
    113 			++obs[ch - 'a'];
    114 		else if (isupper(ch))
    115 			++obs[ch - 'A'];
    116 	}
    117 
    118 	/*
    119 	 * now "dot" the freqs with the observed letter freqs
    120 	 * and keep track of best fit
    121 	 */
    122 	for (try = winner = 0; try < 26; ++try) { /* += 13) { */
    123 		dot = 0;
    124 		for (i = 0; i < 26; i++)
    125 			dot += obs[i] * stdf[(i + try) % 26];
    126 		/* initialize winning score */
    127 		if (try == 0)
    128 			winnerdot = dot;
    129 		if (dot > winnerdot) {
    130 			/* got a new winner! */
    131 			winner = try;
    132 			winnerdot = dot;
    133 		}
    134 	}
    135 
    136 	for (;;) {
    137 		for (i = 0; i < nread; ++i) {
    138 			ch = inbuf[i];
    139 			putchar(ROTATE(ch, winner));
    140 		}
    141 		if (nread < LINELENGTH)
    142 			break;
    143 		if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
    144 			err(1, "reading from stdin");
    145 	}
    146 	exit(0);
    147 }
    148 
    149 void
    150 printit(arg)
    151 	const char *arg;
    152 {
    153 	int ch, rot;
    154 
    155 	if ((rot = atoi(arg)) < 0)
    156 		errx(1, "bad rotation value.");
    157 	while ((ch = getchar()) != EOF)
    158 		putchar(ROTATE(ch, rot));
    159 	exit(0);
    160 }
    161