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
40 static 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
46 static 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 */
70 static double 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
76 static void printit(char *);
77
78 int
main(int argc,char ** argv)79 main(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
147 static void
printit(char * arg)148 printit(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