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