1 /* 2 * Copyright (c) 1989, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Rick Adams. 7 * 8 * Authors: 9 * Stan King, John Eldridge, based on algorithm suggested by 10 * Bob Morris 11 * 29-Sep-82 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 3. All advertising materials mentioning features or use of this software 22 * must display the following acknowledgement: 23 * This product includes software developed by the University of 24 * California, Berkeley and its contributors. 25 * 4. Neither the name of the University nor the names of its contributors 26 * may be used to endorse or promote products derived from this software 27 * without specific prior written permission. 28 * 29 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 30 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 31 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 32 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 33 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 35 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 37 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 38 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 39 * SUCH DAMAGE. 40 * 41 * $FreeBSD: src/games/caesar/caesar.c,v 1.8.2.1 2000/08/17 06:13:06 jhb Exp $ 42 * $DragonFly: src/games/caesar/caesar.c,v 1.3 2003/11/12 14:53:52 eirikn Exp $ 43 * 44 * @(#) Copyright (c) 1989, 1993 The Regents of the University of California. All rights reserved. 45 * @(#)caesar.c 8.1 (Berkeley) 5/31/93 46 * $FreeBSD: src/games/caesar/caesar.c,v 1.8.2.1 2000/08/17 06:13:06 jhb Exp $ 47 */ 48 49 #include <errno.h> 50 #include <math.h> 51 #include <stdio.h> 52 #include <stdlib.h> 53 #include <string.h> 54 #include <ctype.h> 55 #include <unistd.h> 56 57 #define LINELENGTH 2048 58 #define ROTATE(ch, perm) \ 59 isascii(ch) ? ( \ 60 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 61 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch 62 63 /* 64 * letter frequencies (taken from some unix(tm) documentation) 65 * (unix is a trademark of Bell Laboratories) 66 */ 67 double stdf[26] = { 68 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 69 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 70 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 71 }; 72 73 void printit (char *); 74 75 int 76 main(argc, argv) 77 int argc; 78 char **argv; 79 { 80 int ch, dot, i, nread, winnerdot = 0; 81 char *inbuf; 82 int obs[26], try, winner; 83 84 /* revoke setgid privileges */ 85 setgid(getgid()); 86 87 if (argc > 1) 88 printit(argv[1]); 89 90 if (!(inbuf = malloc(LINELENGTH))) { 91 (void)fprintf(stderr, "caesar: out of memory.\n"); 92 exit(1); 93 } 94 95 /* adjust frequency table to weight low probs REAL low */ 96 for (i = 0; i < 26; ++i) 97 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 98 99 /* zero out observation table */ 100 bzero(obs, 26 * sizeof(int)); 101 102 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { 103 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 104 exit(1); 105 } 106 for (i = nread; i--;) { 107 ch = (unsigned char) inbuf[i]; 108 if (isascii(ch)) { 109 if (islower(ch)) 110 ++obs[ch - 'a']; 111 else if (isupper(ch)) 112 ++obs[ch - 'A']; 113 } 114 } 115 116 /* 117 * now "dot" the freqs with the observed letter freqs 118 * and keep track of best fit 119 */ 120 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 121 dot = 0; 122 for (i = 0; i < 26; i++) 123 dot += obs[i] * stdf[(i + try) % 26]; 124 /* initialize winning score */ 125 if (try == 0) 126 winnerdot = dot; 127 if (dot > winnerdot) { 128 /* got a new winner! */ 129 winner = try; 130 winnerdot = dot; 131 } 132 } 133 134 for (;;) { 135 for (i = 0; i < nread; ++i) { 136 ch = (unsigned char) inbuf[i]; 137 putchar(ROTATE(ch, winner)); 138 } 139 if (nread < LINELENGTH) 140 break; 141 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { 142 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 143 exit(1); 144 } 145 } 146 exit(0); 147 } 148 149 void printit(arg) 150 char *arg; 151 { 152 int ch, rot; 153 154 if ((rot = atoi(arg)) < 0) { 155 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 156 exit(1); 157 } 158 while ((ch = getchar()) != EOF) 159 putchar(ROTATE(ch, rot)); 160 exit(0); 161 } 162