caesar.c revision 51287 
1/*
2 * Copyright (c) 1989, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Rick Adams.
7 *
8 * Authors:
9 *	Stan King, John Eldridge, based on algorithm suggested by
10 *	Bob Morris
11 * 29-Sep-82
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 *    notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 *    notice, this list of conditions and the following disclaimer in the
20 *    documentation and/or other materials provided with the distribution.
21 * 3. All advertising materials mentioning features or use of this software
22 *    must display the following acknowledgement:
23 *	This product includes software developed by the University of
24 *	California, Berkeley and its contributors.
25 * 4. Neither the name of the University nor the names of its contributors
26 *    may be used to endorse or promote products derived from this software
27 *    without specific prior written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
30 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
31 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
32 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
33 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
35 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
37 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
38 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
39 * SUCH DAMAGE.
40 */
41
42#ifndef lint
43static const char copyright[] =
44"@(#) Copyright (c) 1989, 1993\n\
45	The Regents of the University of California.  All rights reserved.\n";
46#endif /* not lint */
47
48#ifndef lint
49#if 0
50static const char sccsid[] = "@(#)caesar.c    8.1 (Berkeley) 5/31/93";
51#else
52static const char rcsid[] =
53  "$FreeBSD: head/games/caesar/caesar.c 51287 1999-09-15 01:58:44Z peter $";
54#endif
55#endif /* not lint */
56
57#include <errno.h>
58#include <math.h>
59#include <stdio.h>
60#include <stdlib.h>
61#include <string.h>
62#include <ctype.h>
63#include <unistd.h>
64
65#define	LINELENGTH	2048
66#define	ROTATE(ch, perm) \
67     isascii(ch) ? ( \
68	isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
69	    islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
70
71/*
72 * letter frequencies (taken from some unix(tm) documentation)
73 * (unix is a trademark of Bell Laboratories)
74 */
75double stdf[26] = {
76	7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
77	0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
78	2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
79};
80
81void printit();
82
83int
84main(argc, argv)
85	int argc;
86	char **argv;
87{
88	register int ch, dot, i, nread, winnerdot = 0;
89	register char *inbuf;
90	int obs[26], try, winner;
91
92	/* revoke setgid privileges */
93	setgid(getgid());
94
95	if (argc > 1)
96		printit(argv[1]);
97
98	if (!(inbuf = malloc(LINELENGTH))) {
99		(void)fprintf(stderr, "caesar: out of memory.\n");
100		exit(1);
101	}
102
103	/* adjust frequency table to weight low probs REAL low */
104	for (i = 0; i < 26; ++i)
105		stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
106
107	/* zero out observation table */
108	bzero(obs, 26 * sizeof(int));
109
110	if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
111		(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
112		exit(1);
113	}
114	for (i = nread; i--;) {
115		ch = (unsigned char) inbuf[i];
116		if (isascii(ch)) {
117			if (islower(ch))
118				++obs[ch - 'a'];
119			else if (isupper(ch))
120				++obs[ch - 'A'];
121		}
122	}
123
124	/*
125	 * now "dot" the freqs with the observed letter freqs
126	 * and keep track of best fit
127	 */
128	for (try = winner = 0; try < 26; ++try) { /* += 13) { */
129		dot = 0;
130		for (i = 0; i < 26; i++)
131			dot += obs[i] * stdf[(i + try) % 26];
132		/* initialize winning score */
133		if (try == 0)
134			winnerdot = dot;
135		if (dot > winnerdot) {
136			/* got a new winner! */
137			winner = try;
138			winnerdot = dot;
139		}
140	}
141
142	for (;;) {
143		for (i = 0; i < nread; ++i) {
144			ch = (unsigned char) inbuf[i];
145			putchar(ROTATE(ch, winner));
146		}
147		if (nread < LINELENGTH)
148			break;
149		if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
150			(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
151			exit(1);
152		}
153	}
154	exit(0);
155}
156
157void printit(arg)
158	char *arg;
159{
160	register int ch, rot;
161
162	if ((rot = atoi(arg)) < 0) {
163		(void)fprintf(stderr, "caesar: bad rotation value.\n");
164		exit(1);
165	}
166	while ((ch = getchar()) != EOF)
167		putchar(ROTATE(ch, rot));
168	exit(0);
169}
170