1: /*      $NetBSD: caesar.c,v 1.14 2004/01/27 20:30:29 jsm 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 <sys/cdefs.h>
   41: #ifndef lint
   42: __COPYRIGHT("@(#) Copyright (c) 1989, 1993\n\
   43:         The Regents of the University of California.  All rights reserved.\n");
   44: #endif /* not lint */
   45: 
   46: #ifndef lint
   47: #if 0
   48: static char sccsid[] = "@(#)caesar.c    8.1 (Berkeley) 5/31/93";
   49: #else
   50: __RCSID("$NetBSD: caesar.c,v 1.14 2004/01/27 20:30:29 jsm Exp $");
   51: #endif
   52: #endif /* not lint */
   53: 
   54: #include <ctype.h>
   55: #include <err.h>
   56: #include <errno.h>
   57: #include <math.h>
   58: #include <stdio.h>
   59: #include <string.h>
   60: #include <stdlib.h>
   61: #include <unistd.h>
   62: 
   63: #define LINELENGTH      2048
   64: #define ROTATE(ch, perm) \
   65:         isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
   66:             islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
   67: 
   68: /*
   69:  * letter frequencies (taken from some unix(tm) documentation)
   70:  * (unix is a trademark of Bell Laboratories)
   71:  */
   72: double stdf[26] = {
   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: 
   79: int     main(int, char *[]);
   80: void    printit(const char *) __attribute__((__noreturn__));
   81: 
   82: int
   83: main(argc, argv)
   84:         int argc;
   85:         char **argv;
   86: {
   87:         int ch, i, nread;
   88:         double dot, winnerdot;
   89:         char *inbuf;
   90:         int obs[26], try, winner;
   91: 
   92:         /* revoke setgid privileges */
   93:         setregid(getgid(), getgid());
   94: 
   95:         winnerdot = 0;
   96:         if (argc > 1)
   97:                 printit(argv[1]);
   98: 
   99:         if (!(inbuf = malloc(LINELENGTH)))
  100:                 err(1, NULL);
  101: 
  102:         /* adjust frequency table to weight low probs REAL low */
  103:         for (i = 0; i < 26; ++i)
  104:                 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
  105: 
  106:         /* zero out observation table */
  107:         memset(obs, 0, 26 * sizeof(int));
  108: 
  109:         if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
  110:                 err(1, "reading from stdin");
  111:         for (i = nread; i--;) {
  112:                 ch = inbuf[i];
  113:                 if (islower(ch))
  114:                         ++obs[ch - 'a'];
  115:                 else if (isupper(ch))
  116:                         ++obs[ch - 'A'];
  117:         }
  118: 
  119:         /*
  120:          * now "dot" the freqs with the observed letter freqs
  121:          * and keep track of best fit
  122:          */
  123:         for (try = winner = 0; try < 26; ++try) { /* += 13) { */
  124:                 dot = 0;
  125:                 for (i = 0; i < 26; i++)
  126:                         dot += obs[i] * stdf[(i + try) % 26];
  127:                 /* initialize winning score */
  128:                 if (try == 0)
  129:                         winnerdot = dot;
  130:                 if (dot > winnerdot) {
  131:                         /* got a new winner! */
  132:                         winner = try;
  133:                         winnerdot = dot;
  134:                 }
  135:         }
  136: 
  137:         for (;;) {
  138:                 for (i = 0; i < nread; ++i) {
  139:                         ch = inbuf[i];
  140:                         putchar(ROTATE(ch, winner));
  141:                 }
  142:                 if (nread < LINELENGTH)
  143:                         break;
  144:                 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
  145:                         err(1, "reading from stdin");
  146:         }
  147:         exit(0);
  148: }
  149: 
  150: void
  151: printit(arg)
  152:         const char *arg;
  153: {
  154:         int ch, rot;
  155: 
  156:         if ((rot = atoi(arg)) < 0)
  157:                 errx(1, "bad rotation value.");
  158:         while ((ch = getchar()) != EOF)
  159:                 putchar(ROTATE(ch, rot));
  160:         exit(0);
  161: }