caesar/caesar.c

   1 /*      $NetBSD: caesar.c,v 1.15 2005/05/23 23:02:30 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\n\
  44         The Regents of the University of California.  All rights reserved.\n");
  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 1.15 2005/05/23 23:02:30 rillig Exp $");
  52 #endif
  53 #endif /* not lint */
  54
  55 #include <ctype.h>
  56 #include <err.h>
  57 #include <errno.h>
  58 #include <limits.h>
  59 #include <math.h>
  60 #include <stdio.h>
  61 #include <string.h>
  62 #include <stdlib.h>
  63 #include <unistd.h>
  64
  65 #define NCHARS                  (1 << CHAR_BIT)
  66 #define LETTERS                 (26)
  67
  68 /*
  69  * letter frequencies (taken from some unix(tm) documentation)
  70  * (unix is a trademark of Bell Laboratories)
  71  */
  72 static const unsigned char upper[LETTERS] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  73 static const unsigned char lower[LETTERS] = "abcdefghijklmnopqrstuvwxyz";
  74 static double stdf[LETTERS] = {
  75         7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
  76         0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
  77         2.62, 0.81, 1.88, 0.23,  2.07, 0.06
  78 };
  79
  80 static unsigned char rottbl[NCHARS];
  81
  82
  83 static void
  84 init_rottbl(int rot)
  85 {
  86         size_t i;
  87
  88         rot %= LETTERS;
  89
  90         for (i = 0; i < NCHARS; i++)
  91                 rottbl[i] = (unsigned char)i;
  92
  93         for (i = 0; i < LETTERS; i++)
  94                 rottbl[upper[i]] = upper[(i + rot) % LETTERS];
  95
  96         for (i = 0; i < LETTERS; i++)
  97                 rottbl[lower[i]] = lower[(i + rot) % LETTERS];
  98 }
  99
 100 static void __attribute__((__noreturn__))
 101 printrot(const char *arg)
 102 {
 103         int ch;
 104         long rot;
 105         char *endp;
 106
 107         errno = 0;
 108         rot = strtol(arg, &endp, 10);
 109         if (*endp != '\0') {
 110                 errx(EXIT_FAILURE, "bad rotation value: %s", arg);
 111                 /* NOTREACHED */
 112         }
 113         if (errno == ERANGE || rot < 0 || rot > INT_MAX) {
 114                 errx(EXIT_FAILURE, "rotation value out of range: %s", arg);
 115                 /* NOTREACHED */
 116         }
 117         init_rottbl((int)rot);
 118
 119         while ((ch = getchar()) != EOF) {
 120                 if (putchar(rottbl[ch]) == EOF) {
 121                         err(EXIT_FAILURE, "writing to stdout");
 122                         /* NOTREACHED */
 123                 }
 124         }
 125         exit(EXIT_SUCCESS);
 126         /* NOTREACHED */
 127 }
 128
 129 int
 130 main(int argc, char **argv)
 131 {
 132         ssize_t i, nread, ntotal;
 133         double dot, winnerdot;
 134         int try, winner;
 135         unsigned char inbuf[2048];
 136         unsigned int obs[NCHARS];
 137
 138         /* revoke setgid privileges */
 139         (void)setgid(getgid());
 140
 141         if (argc > 1) {
 142                 printrot(argv[1]);
 143                 /* NOTREACHED */
 144         }
 145
 146         /* adjust frequency table to weight low probs REAL low */
 147         for (i = 0; i < LETTERS; i++)
 148                 stdf[i] = log(stdf[i]) + log(LETTERS / 100.0);
 149
 150         /* zero out observation table */
 151         (void)memset(obs, 0, sizeof(obs));
 152
 153         for (ntotal = 0; (size_t) ntotal < sizeof(inbuf); ntotal += nread) {
 154                 nread = read(STDIN_FILENO, &inbuf[ntotal],
 155                              sizeof(inbuf) - ntotal);
 156                 if (nread < 0) {
 157                         err(EXIT_FAILURE, "reading from stdin");
 158                         /* NOTREACHED */
 159                 }
 160                 if (nread == 0)
 161                         break;
 162         }
 163
 164         for (i = 0; i < ntotal; 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         init_rottbl(winner);
 186
 187         while (ntotal > 0) {
 188                 for (i = 0; i < ntotal; i++) {
 189                         if (putchar(rottbl[inbuf[i]]) == EOF) {
 190                                 err(EXIT_FAILURE, "writing to stdout");
 191                                 /* NOTREACHED */
 192                         }
 193                 }
 194                 if ((ntotal = read(STDIN_FILENO, inbuf, sizeof(inbuf))) < 0) {
 195                         err(EXIT_FAILURE, "reading from stdin");
 196                         /* NOTREACHED */
 197                 }
 198         }
 199         exit(EXIT_FAILURE);
 200         /* NOTREACHED */
 201 }