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 */
56 static 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
62 static void printit(char *);
63
64 int
main(int argc,char ** argv)65 main(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
133 static void
printit(char * arg)134 printit(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