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#include <errno.h>
39#include <math.h>
40#include <stdio.h>
41#include <stdlib.h>
42#include <string.h>
43#include <ctype.h>
44#include <unistd.h>
45
46#define	LINELENGTH	2048
47#define	ROTATE(ch, perm) \
48     isascii(ch) ? ( \
49	isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
50	    islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
51
52/*
53 * letter frequencies (taken from some unix(tm) documentation)
54 * (unix is a trademark of Bell Laboratories)
55 */
56static double stdf[26] = {
57	7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
58	0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
59	2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
60};
61
62static void printit(char *);
63
64int
65main(int argc, char **argv)
66{
67	int ch, dot, i, nread, winnerdot = 0;
68	char *inbuf;
69	int obs[26], try, winner;
70
71	if (argc > 1)
72		printit(argv[1]);
73
74	if (!(inbuf = malloc((size_t)LINELENGTH))) {
75		(void)fprintf(stderr, "caesar: out of memory.\n");
76		exit(1);
77	}
78
79	/* adjust frequency table to weight low probs REAL low */
80	for (i = 0; i < 26; ++i)
81		stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
82
83	/* zero out observation table */
84	bzero(obs, 26 * sizeof(int));
85
86	if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
87		(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
88		exit(1);
89	}
90	for (i = nread; i--;) {
91		ch = (unsigned char) inbuf[i];
92		if (isascii(ch)) {
93			if (islower(ch))
94				++obs[ch - 'a'];
95			else if (isupper(ch))
96				++obs[ch - 'A'];
97		}
98	}
99
100	/*
101	 * now "dot" the freqs with the observed letter freqs
102	 * and keep track of best fit
103	 */
104	for (try = winner = 0; try < 26; ++try) { /* += 13) { */
105		dot = 0;
106		for (i = 0; i < 26; i++)
107			dot += obs[i] * stdf[(i + try) % 26];
108		/* initialize winning score */
109		if (try == 0)
110			winnerdot = dot;
111		if (dot > winnerdot) {
112			/* got a new winner! */
113			winner = try;
114			winnerdot = dot;
115		}
116	}
117
118	for (;;) {
119		for (i = 0; i < nread; ++i) {
120			ch = (unsigned char) inbuf[i];
121			putchar(ROTATE(ch, winner));
122		}
123		if (nread < LINELENGTH)
124			break;
125		if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
126			(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
127			exit(1);
128		}
129	}
130	exit(0);
131}
132
133static void
134printit(char *arg)
135{
136	int ch, rot;
137
138	if ((rot = atoi(arg)) < 0) {
139		(void)fprintf(stderr, "caesar: bad rotation value.\n");
140		exit(1);
141	}
142	while ((ch = getchar()) != EOF)
143		putchar(ROTATE(ch, rot));
144	exit(0);
145}
146