1 /* $OpenBSD: caesar.c,v 1.21 2019/05/15 15:59:24 schwarze Exp $ */
2
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 <ctype.h>
41 #include <err.h>
42 #include <errno.h>
43 #include <math.h>
44 #include <stdio.h>
45 #include <string.h>
46 #include <stdlib.h>
47 #include <unistd.h>
48
49 #define LINELENGTH 2048
50 #define ROTATE(ch, perm) \
51 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
52 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
53
54 /*
55 * letter frequencies
56 */
57 double stdf[26] = {
58 8.1, 1.4, 2.7, 3.8, 13.0, 2.9, 2.0, 5.2, 6.3, 0.13,
59 0.4, 3.4, 2.5, 7.1, 7.9, 1.9, 0.11, 6.8, 6.1, 10.5,
60 2.4, 0.9, 1.5, 0.15, 1.9, 0.07
61 };
62
63 __dead void printit(int);
64
65 int
main(int argc,char * argv[])66 main(int argc, char *argv[])
67 {
68 int ch, i, nread;
69 extern char *__progname;
70 const char *errstr;
71 char *inbuf;
72 int obs[26], try, winner;
73 double dot, winnerdot;
74
75 if (pledge("stdio", NULL) == -1)
76 err(1, "pledge");
77
78 /* check to see if we were called as rot13 */
79 if (strcmp(__progname, "rot13") == 0)
80 printit(13);
81
82 if (argc > 1) {
83 i = strtonum(argv[1], -25, 25, &errstr);
84 if (errstr)
85 errx(1, "rotation is %s: %s", errstr, argv[1]);
86 else
87 printit(i);
88 }
89
90 if (!(inbuf = malloc(LINELENGTH)))
91 err(1, NULL);
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 memset(obs, 0, 26 * sizeof(int));
99
100 nread = 0;
101 while ((nread < LINELENGTH) && ((ch = getchar()) != EOF)) {
102 inbuf[nread++] = ch;
103 if (islower(ch))
104 ++obs[ch - 'a'];
105 else if (isupper(ch))
106 ++obs[ch - 'A'];
107 }
108
109 /*
110 * now "dot" the freqs with the observed letter freqs
111 * and keep track of best fit
112 */
113 winnerdot = 0;
114 for (try = winner = 0; try < 26; ++try) { /* += 13) { */
115 dot = 0;
116 for (i = 0; i < 26; i++)
117 dot += obs[i] * stdf[(i + try) % 26];
118 if (dot > winnerdot) {
119 /* got a new winner! */
120 winner = try;
121 winnerdot = dot;
122 }
123 }
124
125 /* dump the buffer before calling printit */
126 for (i = 0; i < nread; ++i) {
127 ch = inbuf[i];
128 putchar(ROTATE(ch, winner));
129 }
130 printit(winner);
131 }
132
133 void
printit(int rot)134 printit(int rot)
135 {
136 int ch;
137
138 if (rot < 0)
139 rot = rot + 26;
140 while ((ch = getchar()) != EOF)
141 putchar(ROTATE(ch, rot));
142 exit(0);
143 }
144