/* * Copyright (c) 1989 The Regents of the University of California. * All rights reserved. * * This code is derived from software contributed to Berkeley by * Rick Adams. * * Authors: * Stan King, John Eldridge, based on algorithm suggested by * Bob Morris * 29-Sep-82 * * Redistribution and use in source and binary forms are permitted provided * that: (1) source distributions retain this entire copyright notice and * comment, and (2) distributions including binaries display the following * acknowledgement: ``This product includes software developed by the * University of California, Berkeley and its contributors'' in the * documentation or other materials provided with the distribution and in * all advertising materials mentioning features or use of this software. * Neither the name of the University nor the names of its contributors may * be used to endorse or promote products derived from this software without * specific prior written permission. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. */ #ifndef lint char copyright[] = "@(#) Copyright (c) 1989 The Regents of the University of California.\n\ All rights reserved.\n"; #endif /* not lint */ #ifndef lint static char sccsid[] = "@(#)caesar.c 5.4 (Berkeley) 6/1/90"; #endif /* not lint */ #include <math.h> #include <stdio.h> #include <ctype.h> #include <unistd.h> #define LINELENGTH 2048 #define ROTATE(ch, perm) \ isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch /* * letter frequencies (taken from some unix(tm) documentation) * (unix is a trademark of Bell Laboratories) */ double stdf[26] = { 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, }; main(argc, argv) int argc; char **argv; { extern int errno; register int ch, dot, i, nread, winnerdot; register char *inbuf; int obs[26], try, winner; char *malloc(), *strerror(); if (argc > 1) printit(argv[1]); if (!(inbuf = malloc(LINELENGTH))) { (void)fprintf(stderr, "caesar: out of memory.\n"); exit(1); } /* adjust frequency table to weight low probs REAL low */ for (i = 0; i < 26; ++i) stdf[i] = log(stdf[i]) + log(26.0 / 100.0); /* zero out observation table */ bzero(obs, 26 * sizeof(int)); if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); exit(1); } for (i = nread; i--;) { ch = inbuf[i]; if (islower(ch)) ++obs[ch - 'a']; else if (isupper(ch)) ++obs[ch - 'A']; } /* * now "dot" the freqs with the observed letter freqs * and keep track of best fit */ for (try = winner = 0; try < 26; ++try) { /* += 13) { */ dot = 0; for (i = 0; i < 26; i++) dot += obs[i] * stdf[(i + try) % 26]; /* initialize winning score */ if (try == 0) winnerdot = dot; if (dot > winnerdot) { /* got a new winner! */ winner = try; winnerdot = dot; } } for (;;) { for (i = 0; i < nread; ++i) { ch = inbuf[i]; putchar(ROTATE(ch, winner)); } if (nread < LINELENGTH) break; if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); exit(1); } } exit(0); } printit(arg) char *arg; { register int ch, rot; if ((rot = atoi(arg)) < 0) { (void)fprintf(stderr, "caesar: bad rotation value.\n"); exit(1); } while ((ch = getchar()) != EOF) putchar(ROTATE(ch, rot)); exit(0); }