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. Neither the name of the University nor the names of its contributors 22 * may be used to endorse or promote products derived from this software 23 * without specific prior written permission. 24 * 25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 28 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35 * SUCH DAMAGE. 36 * 37 * @(#) Copyright (c) 1989, 1993 The Regents of the University of California. All rights reserved. 38 * @(#)caesar.c 8.1 (Berkeley) 5/31/93 39 * $FreeBSD: head/usr.bin/caesar/caesar.c 241846 2012-10-22 03:06:53Z eadler $ 40 */ 41 42 #include <ctype.h> 43 #include <err.h> 44 #include <errno.h> 45 #include <math.h> 46 #include <stdio.h> 47 #include <stdlib.h> 48 #include <string.h> 49 #include <unistd.h> 50 51 #define LETTERS 26 52 #define LINELENGTH 2048 53 #define ROTATE(ch, perm) \ 54 isascii(ch) ? ( \ 55 isupper(ch) ? ('A' + (ch - 'A' + perm) % LETTERS) : \ 56 islower(ch) ? ('a' + (ch - 'a' + perm) % LETTERS) : ch) : ch 57 58 /* 59 * letter frequencies (taken from some unix(tm) documentation) 60 * (unix is a trademark of Bell Laboratories) 61 */ 62 static double stdf[LETTERS] = { 63 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 64 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 65 2.62, 0.81, 1.88, 0.23, 2.07, 0.06 66 }; 67 68 static void 69 printit(const char *arg) 70 { 71 int ch, rot; 72 73 if ((rot = atoi(arg)) < 0) 74 errx(1, "bad rotation value"); 75 76 while ((ch = getchar()) != EOF) 77 putchar(ROTATE(ch, rot)); 78 exit(0); 79 } 80 81 int 82 main(int argc, char *argv[]) 83 { 84 int ch, dot, i, nread, winnerdot; 85 char *inbuf; 86 int obs[LETTERS], try, winner; 87 88 /* revoke setgid privileges */ 89 setgid(getgid()); 90 91 if (argc > 1) 92 printit(argv[1]); 93 94 if ((inbuf = malloc(LINELENGTH)) == NULL) 95 err(1, "malloc failed"); 96 97 /* adjust frequency table to weight low probs REAL low */ 98 for (i = 0; i < LETTERS; i++) 99 stdf[i] = log(stdf[i]) + log(LETTERS / 100.0); 100 101 /* zero out observation table */ 102 bzero(obs, LETTERS * sizeof(int)); 103 104 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) 105 err(1, "read failed"); 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 winner = 0; 121 winnerdot = 0; 122 for (try = 0; try < LETTERS; try++) { 123 dot = 0; 124 for (i = 0; i < LETTERS; i++) 125 dot += obs[i] * stdf[(i + try) % LETTERS]; 126 /* initialize winning score */ 127 if (try == 0) 128 winnerdot = dot; 129 if (dot > winnerdot) { 130 /* got a new winner! */ 131 winner = try; 132 winnerdot = dot; 133 } 134 } 135 136 for (;;) { 137 for (i = 0; i < nread; ++i) { 138 ch = (unsigned char) inbuf[i]; 139 putchar(ROTATE(ch, winner)); 140 } 141 if (nread < LINELENGTH) 142 break; 143 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) 144 err(1, "read failed"); 145 } 146 exit(0); 147 } 148