1 /* $OpenBSD: caesar.c,v 1.19 2016/02/26 12:10:49 mestre 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. 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 <ctype.h> 41 #include <err.h> 42 #include <errno.h> 43 #include <math.h> 44 #include <stdio.h> 45 #include <string.h> 46 #include <stdlib.h> 47 #include <unistd.h> 48 49 #define LINELENGTH 2048 50 #define ROTATE(ch, perm) \ 51 isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ 52 islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch 53 54 /* 55 * letter frequencies (taken from some unix(tm) documentation) 56 * (unix is a trademark of Bell Laboratories) 57 */ 58 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 __dead void printit(int); 65 66 int 67 main(int argc, char *argv[]) 68 { 69 int ch, i, nread; 70 extern char *__progname; 71 const char *errstr; 72 char *inbuf; 73 int obs[26], try, winner; 74 double dot, winnerdot; 75 76 if (pledge("stdio", NULL) == -1) 77 err(1, "pledge"); 78 79 /* check to see if we were called as rot13 */ 80 if (strcmp(__progname, "rot13") == 0) 81 printit(13); 82 83 if (argc > 1) { 84 i = strtonum(argv[1], 0, 25, &errstr); 85 if (errstr) 86 errx(1, "rotation is %s: %s", errstr, argv[1]); 87 else 88 printit(i); 89 } 90 91 if (!(inbuf = malloc(LINELENGTH))) 92 err(1, NULL); 93 94 /* adjust frequency table to weight low probs REAL low */ 95 for (i = 0; i < 26; ++i) 96 stdf[i] = log(stdf[i]) + log(26.0 / 100.0); 97 98 /* zero out observation table */ 99 memset(obs, 0, 26 * sizeof(int)); 100 101 nread = 0; 102 while ((nread < LINELENGTH) && ((ch = getchar()) != EOF)) { 103 inbuf[nread++] = ch; 104 if (islower(ch)) 105 ++obs[ch - 'a']; 106 else if (isupper(ch)) 107 ++obs[ch - 'A']; 108 } 109 110 /* 111 * now "dot" the freqs with the observed letter freqs 112 * and keep track of best fit 113 */ 114 winnerdot = 0; 115 for (try = winner = 0; try < 26; ++try) { /* += 13) { */ 116 dot = 0; 117 for (i = 0; i < 26; i++) 118 dot += obs[i] * stdf[(i + try) % 26]; 119 if (dot > winnerdot) { 120 /* got a new winner! */ 121 winner = try; 122 winnerdot = dot; 123 } 124 } 125 126 /* dump the buffer before calling printit */ 127 for (i = 0; i < nread; ++i) { 128 ch = inbuf[i]; 129 putchar(ROTATE(ch, winner)); 130 } 131 printit(winner); 132 } 133 134 void 135 printit(int rot) 136 { 137 int ch; 138 139 while ((ch = getchar()) != EOF) 140 putchar(ROTATE(ch, rot)); 141 exit(0); 142 } 143