caesar.c revision 145782 
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#if 0
43#ifndef lint
44static const char copyright[] =
45"@(#) Copyright (c) 1989, 1993\n\
46	The Regents of the University of California.  All rights reserved.\n";
47#endif /* not lint */
48
49#ifndef lint
50static const char sccsid[] = "@(#)caesar.c    8.1 (Berkeley) 5/31/93";
51#endif /* not lint */
52#endif
53#include <sys/cdefs.h>
54__FBSDID("$FreeBSD: head/games/caesar/caesar.c 145782 2005-05-01 19:34:22Z stefanf $");
55
56#include <errno.h>
57#include <math.h>
58#include <stdio.h>
59#include <stdlib.h>
60#include <string.h>
61#include <ctype.h>
62#include <unistd.h>
63
64#define	LINELENGTH	2048
65#define	ROTATE(ch, perm) \
66     isascii(ch) ? ( \
67	isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
68	    islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
69
70/*
71 * letter frequencies (taken from some unix(tm) documentation)
72 * (unix is a trademark of Bell Laboratories)
73 */
74double stdf[26] = {
75	7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
76	0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
77	2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
78};
79
80void printit(char *);
81
82int
83main(int argc, char **argv)
84{
85	int ch, dot, i, nread, winnerdot = 0;
86	char *inbuf;
87	int obs[26], try, winner;
88
89	/* revoke setgid privileges */
90	setgid(getgid());
91
92	if (argc > 1)
93		printit(argv[1]);
94
95	if (!(inbuf = malloc((size_t)LINELENGTH))) {
96		(void)fprintf(stderr, "caesar: out of memory.\n");
97		exit(1);
98	}
99
100	/* adjust frequency table to weight low probs REAL low */
101	for (i = 0; i < 26; ++i)
102		stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
103
104	/* zero out observation table */
105	bzero(obs, 26 * sizeof(int));
106
107	if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
108		(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
109		exit(1);
110	}
111	for (i = nread; i--;) {
112		ch = (unsigned char) inbuf[i];
113		if (isascii(ch)) {
114			if (islower(ch))
115				++obs[ch - 'a'];
116			else if (isupper(ch))
117				++obs[ch - 'A'];
118		}
119	}
120
121	/*
122	 * now "dot" the freqs with the observed letter freqs
123	 * and keep track of best fit
124	 */
125	for (try = winner = 0; try < 26; ++try) { /* += 13) { */
126		dot = 0;
127		for (i = 0; i < 26; i++)
128			dot += obs[i] * stdf[(i + try) % 26];
129		/* initialize winning score */
130		if (try == 0)
131			winnerdot = dot;
132		if (dot > winnerdot) {
133			/* got a new winner! */
134			winner = try;
135			winnerdot = dot;
136		}
137	}
138
139	for (;;) {
140		for (i = 0; i < nread; ++i) {
141			ch = (unsigned char) inbuf[i];
142			putchar(ROTATE(ch, winner));
143		}
144		if (nread < LINELENGTH)
145			break;
146		if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
147			(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
148			exit(1);
149		}
150	}
151	exit(0);
152}
153
154void
155printit(char *arg)
156{
157	int ch, rot;
158
159	if ((rot = atoi(arg)) < 0) {
160		(void)fprintf(stderr, "caesar: bad rotation value.\n");
161		exit(1);
162	}
163	while ((ch = getchar()) != EOF)
164		putchar(ROTATE(ch, rot));
165	exit(0);
166}
167