1 /*
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1989, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Rick Adams.
9 *
10 * Authors:
11 * Stan King, John Eldridge, based on algorithm suggested by
12 * Bob Morris
13 * 29-Sep-82
14 *
15 * Redistribution and use in source and binary forms, with or without
16 * modification, are permitted provided that the following conditions
17 * are met:
18 * 1. Redistributions of source code must retain the above copyright
19 * notice, this list of conditions and the following disclaimer.
20 * 2. Redistributions in binary form must reproduce the above copyright
21 * notice, this list of conditions and the following disclaimer in the
22 * documentation and/or other materials provided with the distribution.
23 * 3. Neither the name of the University nor the names of its contributors
24 * may be used to endorse or promote products derived from this software
25 * without specific prior written permission.
26 *
27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
30 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * SUCH DAMAGE.
38 */
39
40 #include <errno.h>
41 #include <math.h>
42 #include <stdio.h>
43 #include <stdlib.h>
44 #include <string.h>
45 #include <ctype.h>
46 #include <unistd.h>
47
48 #define LINELENGTH 2048
49 #define ROTATE(ch, perm) \
50 isascii(ch) ? ( \
51 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
52 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
53
54 /*
55 * letter frequencies (taken from some unix(tm) documentation)
56 * (unix is a trademark of Bell Laboratories)
57 */
58 static double stdf[26] = {
59 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
60 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
61 2.62, 0.81, 1.88, 0.23, 2.07, 0.06,
62 };
63
64 static void printit(char *);
65
66 int
main(int argc,char ** argv)67 main(int argc, char **argv)
68 {
69 int ch, dot, i, nread, winnerdot = 0;
70 char *inbuf;
71 int obs[26], try, winner;
72
73 if (argc > 1)
74 printit(argv[1]);
75
76 if (!(inbuf = malloc((size_t)LINELENGTH))) {
77 (void)fprintf(stderr, "caesar: out of memory.\n");
78 exit(1);
79 }
80
81 /* adjust frequency table to weight low probs REAL low */
82 for (i = 0; i < 26; ++i)
83 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
84
85 /* zero out observation table */
86 bzero(obs, 26 * sizeof(int));
87
88 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
89 (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
90 exit(1);
91 }
92 for (i = nread; i--;) {
93 ch = (unsigned char) inbuf[i];
94 if (isascii(ch)) {
95 if (islower(ch))
96 ++obs[ch - 'a'];
97 else if (isupper(ch))
98 ++obs[ch - 'A'];
99 }
100 }
101
102 /*
103 * now "dot" the freqs with the observed letter freqs
104 * and keep track of best fit
105 */
106 for (try = winner = 0; try < 26; ++try) { /* += 13) { */
107 dot = 0;
108 for (i = 0; i < 26; i++)
109 dot += obs[i] * stdf[(i + try) % 26];
110 /* initialize winning score */
111 if (try == 0)
112 winnerdot = dot;
113 if (dot > winnerdot) {
114 /* got a new winner! */
115 winner = try;
116 winnerdot = dot;
117 }
118 }
119
120 for (;;) {
121 for (i = 0; i < nread; ++i) {
122 ch = (unsigned char) inbuf[i];
123 putchar(ROTATE(ch, winner));
124 }
125 if (nread < LINELENGTH)
126 break;
127 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
128 (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
129 exit(1);
130 }
131 }
132 exit(0);
133 }
134
135 static void
printit(char * arg)136 printit(char *arg)
137 {
138 int ch, rot;
139
140 if ((rot = atoi(arg)) < 0) {
141 (void)fprintf(stderr, "caesar: bad rotation value.\n");
142 exit(1);
143 }
144 while ((ch = getchar()) != EOF)
145 putchar(ROTATE(ch, rot));
146 exit(0);
147 }
148