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 #include <errno.h> 39 #include <math.h> 40 #include <stdio.h> 41 #include <stdlib.h> 42 #include <string.h> 43 #include <ctype.h> 44 #include <unistd.h> 45 46 #define LINELENGTH 2048 47 #define ROTATE(ch, perm) \ 48 isascii(ch) ? ( \ 49 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 50 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch 51 52 /* 53 * letter frequencies (taken from some unix(tm) documentation) 54 * (unix is a trademark of Bell Laboratories) 55 */ 56 static double stdf[26] = { 57 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 58 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 59 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 60 }; 61 62 static void printit(char *); 63 64 int 65 main(int argc, char **argv) 66 { 67 int ch, dot, i, nread, winnerdot = 0; 68 char *inbuf; 69 int obs[26], try, winner; 70 71 if (argc > 1) 72 printit(argv[1]); 73 74 if (!(inbuf = malloc((size_t)LINELENGTH))) { 75 (void)fprintf(stderr, "caesar: out of memory.\n"); 76 exit(1); 77 } 78 79 /* adjust frequency table to weight low probs REAL low */ 80 for (i = 0; i < 26; ++i) 81 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 82 83 /* zero out observation table */ 84 bzero(obs, 26 * sizeof(int)); 85 86 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 87 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 88 exit(1); 89 } 90 for (i = nread; i--;) { 91 ch = (unsigned char) inbuf[i]; 92 if (isascii(ch)) { 93 if (islower(ch)) 94 ++obs[ch - 'a']; 95 else if (isupper(ch)) 96 ++obs[ch - 'A']; 97 } 98 } 99 100 /* 101 * now "dot" the freqs with the observed letter freqs 102 * and keep track of best fit 103 */ 104 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 105 dot = 0; 106 for (i = 0; i < 26; i++) 107 dot += obs[i] * stdf[(i + try) % 26]; 108 /* initialize winning score */ 109 if (try == 0) 110 winnerdot = dot; 111 if (dot > winnerdot) { 112 /* got a new winner! */ 113 winner = try; 114 winnerdot = dot; 115 } 116 } 117 118 for (;;) { 119 for (i = 0; i < nread; ++i) { 120 ch = (unsigned char) inbuf[i]; 121 putchar(ROTATE(ch, winner)); 122 } 123 if (nread < LINELENGTH) 124 break; 125 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 126 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 127 exit(1); 128 } 129 } 130 exit(0); 131 } 132 133 static void 134 printit(char *arg) 135 { 136 int ch, rot; 137 138 if ((rot = atoi(arg)) < 0) { 139 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 140 exit(1); 141 } 142 while ((ch = getchar()) != EOF) 143 putchar(ROTATE(ch, rot)); 144 exit(0); 145 } 146