1 /* $NetBSD: caesar.c,v 1.4 1996/02/06 22:47:15 jtc 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 #ifndef lint 45 static char copyright[] = 46 "@(#) 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 static char rcsid[] = "$NetBSD: caesar.c,v 1.4 1996/02/06 22:47:15 jtc Exp $"; 55 #endif 56 #endif /* not lint */ 57 58 #include <math.h> 59 #include <stdio.h> 60 #include <ctype.h> 61 #include <unistd.h> 62 #include <errno.h> 63 64 #define LINELENGTH 2048 65 #define ROTATE(ch, perm) \ 66 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 67 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch 68 69 /* 70 * letter frequencies (taken from some unix(tm) documentation) 71 * (unix is a trademark of Bell Laboratories) 72 */ 73 double stdf[26] = { 74 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 75 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 76 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 77 }; 78 79 main(argc, argv) 80 int argc; 81 char **argv; 82 { 83 register int ch, dot, i, nread, winnerdot; 84 register char *inbuf; 85 int obs[26], try, winner; 86 char *malloc(), *strerror(); 87 88 if (argc > 1) 89 printit(argv[1]); 90 91 if (!(inbuf = malloc(LINELENGTH))) { 92 (void)fprintf(stderr, "caesar: out of memory.\n"); 93 exit(1); 94 } 95 96 /* adjust frequency table to weight low probs REAL low */ 97 for (i = 0; i < 26; ++i) 98 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 99 100 /* zero out observation table */ 101 bzero(obs, 26 * sizeof(int)); 102 103 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { 104 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 105 exit(1); 106 } 107 for (i = nread; i--;) { 108 ch = inbuf[i]; 109 if (islower(ch)) 110 ++obs[ch - 'a']; 111 else if (isupper(ch)) 112 ++obs[ch - 'A']; 113 } 114 115 /* 116 * now "dot" the freqs with the observed letter freqs 117 * and keep track of best fit 118 */ 119 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 120 dot = 0; 121 for (i = 0; i < 26; i++) 122 dot += obs[i] * stdf[(i + try) % 26]; 123 /* initialize winning score */ 124 if (try == 0) 125 winnerdot = dot; 126 if (dot > winnerdot) { 127 /* got a new winner! */ 128 winner = try; 129 winnerdot = dot; 130 } 131 } 132 133 for (;;) { 134 for (i = 0; i < nread; ++i) { 135 ch = inbuf[i]; 136 putchar(ROTATE(ch, winner)); 137 } 138 if (nread < LINELENGTH) 139 break; 140 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { 141 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 142 exit(1); 143 } 144 } 145 exit(0); 146 } 147 148 printit(arg) 149 char *arg; 150 { 151 register int ch, rot; 152 153 if ((rot = atoi(arg)) < 0) { 154 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 155 exit(1); 156 } 157 while ((ch = getchar()) != EOF) 158 putchar(ROTATE(ch, rot)); 159 exit(0); 160 } 161