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 38 #if 0 39 #ifndef lint 40 static const char copyright[] = 41 "@(#) Copyright (c) 1989, 1993\n\ 42 The Regents of the University of California. All rights reserved.\n"; 43 #endif /* not lint */ 44 45 #ifndef lint 46 static const char sccsid[] = "@(#)caesar.c 8.1 (Berkeley) 5/31/93"; 47 #endif /* not lint */ 48 #endif 49 #include <sys/cdefs.h> 50 #include <errno.h> 51 #include <math.h> 52 #include <stdio.h> 53 #include <stdlib.h> 54 #include <string.h> 55 #include <ctype.h> 56 #include <unistd.h> 57 58 #define LINELENGTH 2048 59 #define ROTATE(ch, perm) \ 60 isascii(ch) ? ( \ 61 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 62 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch 63 64 /* 65 * letter frequencies (taken from some unix(tm) documentation) 66 * (unix is a trademark of Bell Laboratories) 67 */ 68 static double stdf[26] = { 69 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 70 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 71 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 72 }; 73 74 static void printit(char *); 75 76 int 77 main(int argc, char **argv) 78 { 79 int ch, dot, i, nread, winnerdot = 0; 80 char *inbuf; 81 int obs[26], try, winner; 82 83 if (argc > 1) 84 printit(argv[1]); 85 86 if (!(inbuf = malloc((size_t)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, (size_t)LINELENGTH)) < 0) { 99 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 100 exit(1); 101 } 102 for (i = nread; i--;) { 103 ch = (unsigned char) inbuf[i]; 104 if (isascii(ch)) { 105 if (islower(ch)) 106 ++obs[ch - 'a']; 107 else if (isupper(ch)) 108 ++obs[ch - 'A']; 109 } 110 } 111 112 /* 113 * now "dot" the freqs with the observed letter freqs 114 * and keep track of best fit 115 */ 116 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 117 dot = 0; 118 for (i = 0; i < 26; i++) 119 dot += obs[i] * stdf[(i + try) % 26]; 120 /* initialize winning score */ 121 if (try == 0) 122 winnerdot = dot; 123 if (dot > winnerdot) { 124 /* got a new winner! */ 125 winner = try; 126 winnerdot = dot; 127 } 128 } 129 130 for (;;) { 131 for (i = 0; i < nread; ++i) { 132 ch = (unsigned char) inbuf[i]; 133 putchar(ROTATE(ch, winner)); 134 } 135 if (nread < LINELENGTH) 136 break; 137 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 138 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 139 exit(1); 140 } 141 } 142 exit(0); 143 } 144 145 static void 146 printit(char *arg) 147 { 148 int ch, rot; 149 150 if ((rot = atoi(arg)) < 0) { 151 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 152 exit(1); 153 } 154 while ((ch = getchar()) != EOF) 155 putchar(ROTATE(ch, rot)); 156 exit(0); 157 } 158