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 #include <errno.h>
51 #include <math.h>
52 #include <stdio.h>
53 #include <stdlib.h>
54 #include <string.h>
55 #include <ctype.h>
56 #include <unistd.h>
57
58 #define LINELENGTH 2048
59 #define ROTATE(ch, perm) \
60 isascii(ch) ? ( \
61 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
62 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
63
64 /*
65 * letter frequencies (taken from some unix(tm) documentation)
66 * (unix is a trademark of Bell Laboratories)
67 */
68 static double stdf[26] = {
69 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
70 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
71 2.62, 0.81, 1.88, 0.23, 2.07, 0.06,
72 };
73
74 static void printit(char *);
75
76 int
main(int argc,char ** argv)77 main(int argc, char **argv)
78 {
79 int ch, dot, i, nread, winnerdot = 0;
80 char *inbuf;
81 int obs[26], try, winner;
82
83 if (argc > 1)
84 printit(argv[1]);
85
86 if (!(inbuf = malloc((size_t)LINELENGTH))) {
87 (void)fprintf(stderr, "caesar: out of memory.\n");
88 exit(1);
89 }
90
91 /* adjust frequency table to weight low probs REAL low */
92 for (i = 0; i < 26; ++i)
93 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
94
95 /* zero out observation table */
96 bzero(obs, 26 * sizeof(int));
97
98 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
99 (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
100 exit(1);
101 }
102 for (i = nread; i--;) {
103 ch = (unsigned char) inbuf[i];
104 if (isascii(ch)) {
105 if (islower(ch))
106 ++obs[ch - 'a'];
107 else if (isupper(ch))
108 ++obs[ch - 'A'];
109 }
110 }
111
112 /*
113 * now "dot" the freqs with the observed letter freqs
114 * and keep track of best fit
115 */
116 for (try = winner = 0; try < 26; ++try) { /* += 13) { */
117 dot = 0;
118 for (i = 0; i < 26; i++)
119 dot += obs[i] * stdf[(i + try) % 26];
120 /* initialize winning score */
121 if (try == 0)
122 winnerdot = dot;
123 if (dot > winnerdot) {
124 /* got a new winner! */
125 winner = try;
126 winnerdot = dot;
127 }
128 }
129
130 for (;;) {
131 for (i = 0; i < nread; ++i) {
132 ch = (unsigned char) inbuf[i];
133 putchar(ROTATE(ch, winner));
134 }
135 if (nread < LINELENGTH)
136 break;
137 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
138 (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
139 exit(1);
140 }
141 }
142 exit(0);
143 }
144
145 static void
printit(char * arg)146 printit(char *arg)
147 {
148 int ch, rot;
149
150 if ((rot = atoi(arg)) < 0) {
151 (void)fprintf(stderr, "caesar: bad rotation value.\n");
152 exit(1);
153 }
154 while ((ch = getchar()) != EOF)
155 putchar(ROTATE(ch, rot));
156 exit(0);
157 }
158