1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
/* $OpenBSD: caesar.c,v 1.20 2017/08/10 17:24:30 tedu Exp $ */
/*
* Copyright (c) 1989, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Rick Adams.
*
* Authors:
* Stan King, John Eldridge, based on algorithm suggested by
* Bob Morris
* 29-Sep-82
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#define LINELENGTH 2048
#define ROTATE(ch, perm) \
isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
/*
* letter frequencies
*/
double stdf[26] = {
8.1, 1.4, 2.7, 3.8, 13.0, 2.9, 2.0, 5.2, 6.3, 0.13,
0.4, 3.4, 2.5, 7.1, 7.9, 1.9, 0.11, 6.8, 6.1, 10.5,
2.4, 0.9, 1.5, 0.15, 1.9, 0.07
};
__dead void printit(int);
int
main(int argc, char *argv[])
{
int ch, i, nread;
extern char *__progname;
const char *errstr;
char *inbuf;
int obs[26], try, winner;
double dot, winnerdot;
if (pledge("stdio", NULL) == -1)
err(1, "pledge");
/* check to see if we were called as rot13 */
if (strcmp(__progname, "rot13") == 0)
printit(13);
if (argc > 1) {
i = strtonum(argv[1], 0, 25, &errstr);
if (errstr)
errx(1, "rotation is %s: %s", errstr, argv[1]);
else
printit(i);
}
if (!(inbuf = malloc(LINELENGTH)))
err(1, NULL);
/* adjust frequency table to weight low probs REAL low */
for (i = 0; i < 26; ++i)
stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
/* zero out observation table */
memset(obs, 0, 26 * sizeof(int));
nread = 0;
while ((nread < LINELENGTH) && ((ch = getchar()) != EOF)) {
inbuf[nread++] = ch;
if (islower(ch))
++obs[ch - 'a'];
else if (isupper(ch))
++obs[ch - 'A'];
}
/*
* now "dot" the freqs with the observed letter freqs
* and keep track of best fit
*/
winnerdot = 0;
for (try = winner = 0; try < 26; ++try) { /* += 13) { */
dot = 0;
for (i = 0; i < 26; i++)
dot += obs[i] * stdf[(i + try) % 26];
if (dot > winnerdot) {
/* got a new winner! */
winner = try;
winnerdot = dot;
}
}
/* dump the buffer before calling printit */
for (i = 0; i < nread; ++i) {
ch = inbuf[i];
putchar(ROTATE(ch, winner));
}
printit(winner);
}
void
printit(int rot)
{
int ch;
while ((ch = getchar()) != EOF)
putchar(ROTATE(ch, rot));
exit(0);
}
|
