1 /* 2 * SPDX-License-Identifier: BSD-3-Clause 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. Neither the name of the University nor the names of its contributors 24 * may be used to endorse or promote products derived from this software 25 * without specific prior written permission. 26 * 27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 30 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 37 * SUCH DAMAGE. 38 */ 39 40 #include <errno.h> 41 #include <math.h> 42 #include <stdio.h> 43 #include <stdlib.h> 44 #include <string.h> 45 #include <ctype.h> 46 #include <unistd.h> 47 48 #define LINELENGTH 2048 49 #define ROTATE(ch, perm) \ 50 isascii(ch) ? ( \ 51 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 52 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch 53 54 /* 55 * letter frequencies (taken from some unix(tm) documentation) 56 * (unix is a trademark of Bell Laboratories) 57 */ 58 static double stdf[26] = { 59 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 60 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 61 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, 62 }; 63 64 static void printit(char *); 65 66 int 67 main(int argc, char **argv) 68 { 69 int ch, dot, i, nread, winnerdot = 0; 70 char *inbuf; 71 int obs[26], try, winner; 72 73 if (argc > 1) 74 printit(argv[1]); 75 76 if (!(inbuf = malloc((size_t)LINELENGTH))) { 77 (void)fprintf(stderr, "caesar: out of memory.\n"); 78 exit(1); 79 } 80 81 /* adjust frequency table to weight low probs REAL low */ 82 for (i = 0; i < 26; ++i) 83 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 84 85 /* zero out observation table */ 86 bzero(obs, 26 * sizeof(int)); 87 88 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 89 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 90 exit(1); 91 } 92 for (i = nread; i--;) { 93 ch = (unsigned char) inbuf[i]; 94 if (isascii(ch)) { 95 if (islower(ch)) 96 ++obs[ch - 'a']; 97 else if (isupper(ch)) 98 ++obs[ch - 'A']; 99 } 100 } 101 102 /* 103 * now "dot" the freqs with the observed letter freqs 104 * and keep track of best fit 105 */ 106 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 107 dot = 0; 108 for (i = 0; i < 26; i++) 109 dot += obs[i] * stdf[(i + try) % 26]; 110 /* initialize winning score */ 111 if (try == 0) 112 winnerdot = dot; 113 if (dot > winnerdot) { 114 /* got a new winner! */ 115 winner = try; 116 winnerdot = dot; 117 } 118 } 119 120 for (;;) { 121 for (i = 0; i < nread; ++i) { 122 ch = (unsigned char) inbuf[i]; 123 putchar(ROTATE(ch, winner)); 124 } 125 if (nread < LINELENGTH) 126 break; 127 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) { 128 (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); 129 exit(1); 130 } 131 } 132 exit(0); 133 } 134 135 static void 136 printit(char *arg) 137 { 138 int ch, rot; 139 140 if ((rot = atoi(arg)) < 0) { 141 (void)fprintf(stderr, "caesar: bad rotation value.\n"); 142 exit(1); 143 } 144 while ((ch = getchar()) != EOF) 145 putchar(ROTATE(ch, rot)); 146 exit(0); 147 } 148