1 /* 2 * Copyright (c) 1989 The Regents of the University of California. 3 * 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 42 #ifndef lint 43 char copyright[] = 44 "@(#) Copyright (c) 1989 The Regents of the University of California.\n\ 45 All rights reserved.\n"; 46 #endif /* not lint */ 47 48 #ifndef lint 49 /*static char sccsid[] = "from: @(#)caesar.c 5.4 (Berkeley) 6/1/90";*/ 50 static char rcsid[] = "$Id: caesar.c,v 1.2 1993/08/01 18:55:37 mycroft Exp $"; 51 #endif /* not lint */ 52 53 #include <math.h> 54 #include <stdio.h> 55 #include <ctype.h> 56 #include <unistd.h> 57 58 #define LINELENGTH 2048 59 #define ROTATE(ch, perm) \ 60 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 61 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : 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 main(argc, argv) 74 int argc; 75 char **argv; 76 { 77 extern int errno; 78 register int ch, dot, i, nread, winnerdot; 79 register char *inbuf; 80 int obs[26], try, winner; 81 char *malloc(), *strerror(); 82 83 if (argc > 1) 84 printit(argv[1]); 85 86 if (!(inbuf = malloc(LINELENGTH))) { 87 (void)fprintf(stderr, "caesar: out of memory.\n"); 88 exit(1); 89 } 90 91 /* adjust frequency table to weight low probs REAL low */ 92 for (i = 0; i < 26; ++i) 93 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 94 95 /* zero out observation table */ 96 bzero(obs, 26 * sizeof(int)); 97 98 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { 99 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 100 exit(1); 101 } 102 for (i = nread; i--;) { 103 ch = inbuf[i]; 104 if (islower(ch)) 105 ++obs[ch - 'a']; 106 else if (isupper(ch)) 107 ++obs[ch - 'A']; 108 } 109 110 /* 111 * now "dot" the freqs with the observed letter freqs 112 * and keep track of best fit 113 */ 114 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 115 dot = 0; 116 for (i = 0; i < 26; i++) 117 dot += obs[i] * stdf[(i + try) % 26]; 118 /* initialize winning score */ 119 if (try == 0) 120 winnerdot = dot; 121 if (dot > winnerdot) { 122 /* got a new winner! */ 123 winner = try; 124 winnerdot = dot; 125 } 126 } 127 128 for (;;) { 129 for (i = 0; i < nread; ++i) { 130 ch = inbuf[i]; 131 putchar(ROTATE(ch, winner)); 132 } 133 if (nread < LINELENGTH) 134 break; 135 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { 136 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 137 exit(1); 138 } 139 } 140 exit(0); 141 } 142 143 printit(arg) 144 char *arg; 145 { 146 register int ch, rot; 147 148 if ((rot = atoi(arg)) < 0) { 149 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 150 exit(1); 151 } 152 while ((ch = getchar()) != EOF) 153 putchar(ROTATE(ch, rot)); 154 exit(0); 155 } 156