1 /* $NetBSD: caesar.c,v 1.11 2000/05/08 07:56:02 mycroft 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. All advertising materials mentioning features or use of this software 24 * must display the following acknowledgement: 25 * This product includes software developed by the University of 26 * California, Berkeley and its contributors. 27 * 4. Neither the name of the University nor the names of its contributors 28 * may be used to endorse or promote products derived from this software 29 * without specific prior written permission. 30 * 31 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 32 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 33 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 34 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 35 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 36 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 37 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 38 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 39 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 40 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 41 * SUCH DAMAGE. 42 */ 43 44 #include <sys/cdefs.h> 45 #ifndef lint 46 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\n\ 47 The Regents of the University of California. All rights reserved.\n"); 48 #endif /* not lint */ 49 50 #ifndef lint 51 #if 0 52 static char sccsid[] = "@(#)caesar.c 8.1 (Berkeley) 5/31/93"; 53 #else 54 __RCSID("$NetBSD: caesar.c,v 1.11 2000/05/08 07:56:02 mycroft Exp $"); 55 #endif 56 #endif /* not lint */ 57 58 #include <ctype.h> 59 #include <err.h> 60 #include <errno.h> 61 #include <math.h> 62 #include <stdio.h> 63 #include <string.h> 64 #include <stdlib.h> 65 #include <unistd.h> 66 67 #define LINELENGTH 2048 68 #define ROTATE(ch, perm) \ 69 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 70 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch 71 72 /* 73 * letter frequencies (taken from some unix(tm) documentation) 74 * (unix is a trademark of Bell Laboratories) 75 */ 76 double stdf[26] = { 77 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 78 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 79 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 80 }; 81 82 83 int main __P((int, char *[])); 84 void printit __P((const char *)) __attribute__((__noreturn__)); 85 86 int 87 main(argc, argv) 88 int argc; 89 char **argv; 90 { 91 int ch, dot, i, nread, winnerdot; 92 char *inbuf; 93 int obs[26], try, winner; 94 95 /* revoke setgid privileges */ 96 setgid(getgid()); 97 98 winnerdot = 0; 99 if (argc > 1) 100 printit(argv[1]); 101 102 if (!(inbuf = malloc(LINELENGTH))) 103 err(1, NULL); 104 105 /* adjust frequency table to weight low probs REAL low */ 106 for (i = 0; i < 26; ++i) 107 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 108 109 /* zero out observation table */ 110 memset(obs, 0, 26 * sizeof(int)); 111 112 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) 113 err(1, "reading from stdin"); 114 for (i = nread; i--;) { 115 ch = inbuf[i]; 116 if (islower(ch)) 117 ++obs[ch - 'a']; 118 else if (isupper(ch)) 119 ++obs[ch - 'A']; 120 } 121 122 /* 123 * now "dot" the freqs with the observed letter freqs 124 * and keep track of best fit 125 */ 126 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 127 dot = 0; 128 for (i = 0; i < 26; i++) 129 dot += obs[i] * stdf[(i + try) % 26]; 130 /* initialize winning score */ 131 if (try == 0) 132 winnerdot = dot; 133 if (dot > winnerdot) { 134 /* got a new winner! */ 135 winner = try; 136 winnerdot = dot; 137 } 138 } 139 140 for (;;) { 141 for (i = 0; i < nread; ++i) { 142 ch = inbuf[i]; 143 putchar(ROTATE(ch, winner)); 144 } 145 if (nread < LINELENGTH) 146 break; 147 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) 148 err(1, "reading from stdin"); 149 } 150 exit(0); 151 } 152 153 void 154 printit(arg) 155 const char *arg; 156 { 157 int ch, rot; 158 159 if ((rot = atoi(arg)) < 0) 160 errx(1, "bad rotation value."); 161 while ((ch = getchar()) != EOF) 162 putchar(ROTATE(ch, rot)); 163 exit(0); 164 } 165