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 #endif 46 #include <sys/cdefs.h> 47 #include <errno.h> 48 #include <math.h> 49 #include <stdio.h> 50 #include <stdlib.h> 51 #include <string.h> 52 #include <ctype.h> 53 #include <unistd.h> 54 55 #define LINELENGTH 2048 56 #define ROTATE(ch, perm) \ 57 isascii(ch) ? ( \ 58 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 59 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch 60 61 /* 62 * letter frequencies (taken from some unix(tm) documentation) 63 * (unix is a trademark of Bell Laboratories) 64 */ 65 static double stdf[26] = { 66 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 67 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 68 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 69 }; 70 71 static void printit(char *); 72 73 int 74 main(int argc, char **argv) 75 { 76 int ch, dot, i, nread, winnerdot = 0; 77 char *inbuf; 78 int obs[26], try, winner; 79 80 if (argc > 1) 81 printit(argv[1]); 82 83 if (!(inbuf = malloc((size_t)LINELENGTH))) { 84 (void)fprintf(stderr, "caesar: out of memory.\n"); 85 exit(1); 86 } 87 88 /* adjust frequency table to weight low probs REAL low */ 89 for (i = 0; i < 26; ++i) 90 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 91 92 /* zero out observation table */ 93 bzero(obs, 26 * sizeof(int)); 94 95 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 96 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 97 exit(1); 98 } 99 for (i = nread; i--;) { 100 ch = (unsigned char) inbuf[i]; 101 if (isascii(ch)) { 102 if (islower(ch)) 103 ++obs[ch - 'a']; 104 else if (isupper(ch)) 105 ++obs[ch - 'A']; 106 } 107 } 108 109 /* 110 * now "dot" the freqs with the observed letter freqs 111 * and keep track of best fit 112 */ 113 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 114 dot = 0; 115 for (i = 0; i < 26; i++) 116 dot += obs[i] * stdf[(i + try) % 26]; 117 /* initialize winning score */ 118 if (try == 0) 119 winnerdot = dot; 120 if (dot > winnerdot) { 121 /* got a new winner! */ 122 winner = try; 123 winnerdot = dot; 124 } 125 } 126 127 for (;;) { 128 for (i = 0; i < nread; ++i) { 129 ch = (unsigned char) inbuf[i]; 130 putchar(ROTATE(ch, winner)); 131 } 132 if (nread < LINELENGTH) 133 break; 134 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 135 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 136 exit(1); 137 } 138 } 139 exit(0); 140 } 141 142 static void 143 printit(char *arg) 144 { 145 int ch, rot; 146 147 if ((rot = atoi(arg)) < 0) { 148 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 149 exit(1); 150 } 151 while ((ch = getchar()) != EOF) 152 putchar(ROTATE(ch, rot)); 153 exit(0); 154 } 155