caesar/caesar.c

   1 /*      $NetBSD: caesar.c,v 1.23 2021/05/01 20:21:25 rillig 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  *      Roland Illig, 2005
  15  *
  16  * Redistribution and use in source and binary forms, with or without
  17  * modification, are permitted provided that the following conditions
  18  * are met:
  19  * 1. Redistributions of source code must retain the above copyright
  20  *    notice, this list of conditions and the following disclaimer.
  21  * 2. Redistributions in binary form must reproduce the above copyright
  22  *    notice, this list of conditions and the following disclaimer in the
  23  *    documentation and/or other materials provided with the distribution.
  24  * 3. Neither the name of the University nor the names of its contributors
  25  *    may be used to endorse or promote products derived from this software
  26  *    without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  38  * SUCH DAMAGE.
  39  */
  40
  41 #include <sys/cdefs.h>
  42 #ifndef lint
  43 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\
  44  The Regents of the University of California.  All rights reserved.");
  45 #endif /* not lint */
  46
  47 #ifndef lint
  48 #if 0
  49 static char sccsid[] = "@(#)caesar.c    8.1 (Berkeley) 5/31/93";
  50 #else
  51 __RCSID("$NetBSD: caesar.c,v 1.23 2021/05/01 20:21:25 rillig Exp $");
  52 #endif
  53 #endif /* not lint */
  54
  55 #include <err.h>
  56 #include <errno.h>
  57 #include <limits.h>
  58 #include <math.h>
  59 #include <stdio.h>
  60 #include <string.h>
  61 #include <stdlib.h>
  62
  63 #define NCHARS                  (1 << CHAR_BIT)
  64 #define LETTERS                 (26)
  65
  66 /*
  67  * letter frequencies (taken from some unix(tm) documentation)
  68  * (unix is a trademark of Bell Laboratories)
  69  */
  70 static const unsigned char upper[LETTERS] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  71 static const unsigned char lower[LETTERS] = "abcdefghijklmnopqrstuvwxyz";
  72 static double stdf[LETTERS] = {
  73         7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
  74         0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
  75         2.62, 0.81, 1.88, 0.23,  2.07, 0.06
  76 };
  77
  78 static unsigned char rottbl[NCHARS];
  79
  80
  81 static void
  82 init_rottbl(unsigned int rot)
  83 {
  84         size_t i;
  85
  86         rot %= LETTERS;         /* prevent integer overflow */
  87
  88         for (i = 0; i < NCHARS; i++)
  89                 rottbl[i] = (unsigned char)i;
  90
  91         for (i = 0; i < LETTERS; i++)
  92                 rottbl[upper[i]] = upper[(i + rot) % LETTERS];
  93
  94         for (i = 0; i < LETTERS; i++)
  95                 rottbl[lower[i]] = lower[(i + rot) % LETTERS];
  96 }
  97
  98 static void
  99 print_file(void)
 100 {
 101         int ch;
 102
 103         while ((ch = getchar()) != EOF) {
 104                 if (putchar(rottbl[ch]) == EOF) {
 105                         err(EXIT_FAILURE, "<stdout>");
 106                         /* NOTREACHED */
 107                 }
 108         }
 109 }
 110
 111 static void
 112 print_array(const unsigned char *a, size_t len)
 113 {
 114         size_t i;
 115
 116         for (i = 0; i < len; i++) {
 117                 if (putchar(rottbl[a[i]]) == EOF) {
 118                         err(EXIT_FAILURE, "<stdout>");
 119                         /* NOTREACHED */
 120                 }
 121         }
 122 }
 123
 124 static unsigned int
 125 get_rotation(const char *arg)
 126 {
 127         long rot;
 128         char *endp;
 129
 130         errno = 0;
 131         rot = strtol(arg, &endp, 10);
 132         if (errno == 0 && (arg[0] == '\0' || *endp != '\0'))
 133                 errno = EINVAL;
 134         if (errno == 0 && (rot < 0 || rot > INT_MAX))
 135                 errno = ERANGE;
 136         if (errno)
 137                 err(EXIT_FAILURE, "Bad rotation value `%s'", arg);
 138         return (unsigned int)rot;
 139 }
 140
 141 static void
 142 guess_and_rotate(void)
 143 {
 144         unsigned char inbuf[2048];
 145         unsigned int obs[NCHARS];
 146         size_t i, nread;
 147         double dot, winnerdot;
 148         unsigned int try, winner;
 149         int ch;
 150
 151         /* adjust frequency table to weight low probs REAL low */
 152         for (i = 0; i < LETTERS; i++)
 153                 stdf[i] = log(stdf[i]) + log(LETTERS / 100.0);
 154
 155         /* zero out observation table */
 156         (void)memset(obs, 0, sizeof(obs));
 157
 158         for (nread = 0; nread < sizeof(inbuf); nread++) {
 159                 if ((ch = getchar()) == EOF)
 160                         break;
 161                 inbuf[nread] = (unsigned char) ch;
 162         }
 163
 164         for (i = 0; i < nread; i++)
 165                 obs[inbuf[i]]++;
 166
 167         /*
 168          * now "dot" the freqs with the observed letter freqs
 169          * and keep track of best fit
 170          */
 171         winner = 0;
 172         winnerdot = 0.0;
 173         for (try = 0; try < LETTERS; try++) {
 174                 dot = 0.0;
 175                 for (i = 0; i < LETTERS; i++)
 176                         dot += (obs[upper[i]] + obs[lower[i]])
 177                              * stdf[(i + try) % LETTERS];
 178
 179                 if (try == 0 || dot > winnerdot) {
 180                         /* got a new winner! */
 181                         winner = try;
 182                         winnerdot = dot;
 183                 }
 184         }
 185
 186         init_rottbl(winner);
 187         print_array(inbuf, nread);
 188         print_file();
 189 }
 190
 191 int
 192 main(int argc, char **argv)
 193 {
 194
 195         if (argc == 1) {
 196                 guess_and_rotate();
 197         } else if (argc == 2) {
 198                 init_rottbl(get_rotation(argv[1]));
 199                 print_file();
 200         } else {
 201                 (void)fprintf(stderr, "usage: caesar [rotation]\n");
 202                 exit(EXIT_FAILURE);
 203                 /* NOTREACHED */
 204         }
 205
 206         if (ferror(stdin)) {
 207                 errx(EXIT_FAILURE, "<stdin>");
 208                 /* NOTREACHED */
 209         }
 210
 211         (void)fflush(stdout);
 212         if (ferror(stdout)) {
 213                 errx(EXIT_FAILURE, "<stdout>");
 214                 /* NOTREACHED */
 215         }
 216
 217         return 0;
 218 }