/* $OpenBSD: caesar.c,v 1.11 2002/05/31 04:21:30 pjanzen Exp $ */ /* * Copyright (c) 1989, 1993 * 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, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by the University of * California, Berkeley and its contributors. * 4. 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 BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #ifndef lint static char copyright[] = "@(#) Copyright (c) 1989, 1993\n\ The Regents of the University of California. All rights reserved.\n"; #endif /* not lint */ #ifndef lint #if 0 static char sccsid[] = "@(#)caesar.c 8.1 (Berkeley) 5/31/93"; #else static char rcsid[] = "$OpenBSD: caesar.c,v 1.11 2002/05/31 04:21:30 pjanzen Exp $"; #endif #endif /* not lint */ #include #include #include #include #include #include #include #include #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, }; void printit(int); void usage(void); int main(argc, argv) int argc; char **argv; { int ch, dot, i, nread, winnerdot; char *inbuf, *p, **av; int obs[26], try, winner; /* check to see if we were called as rot13 */ av = argv; p = strrchr(*av, '/'); if (p++ == NULL) p = *av; if (strcmp(p,"rot13") == 0) printit(13); if (argc > 1) { if ((i = atoi(argv[1]))) printit(i); else usage(); } if (!(inbuf = malloc(LINELENGTH))) err(1, NULL); /* 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 */ memset(obs, 0, 26 * sizeof(int)); nread = 0; while ((nread < LINELENGTH) && ((ch = getchar()) != EOF)) { inbuf[nread++] = ch; 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 */ winnerdot = 0; for (try = winner = 0; try < 26; ++try) { /* += 13) { */ dot = 0; for (i = 0; i < 26; i++) dot += obs[i] * stdf[(i + try) % 26]; if (dot > winnerdot) { /* got a new winner! */ winner = try; winnerdot = dot; } } /* dump the buffer before calling printit */ for (i = 0; i < nread; ++i) { ch = inbuf[i]; putchar(ROTATE(ch, winner)); } printit(winner); /* NOT REACHED */ } void printit(rot) int rot; { int ch; if ((rot < 0) || ( rot >= 26)) errx(1, "bad rotation value"); while ((ch = getchar()) != EOF) putchar(ROTATE(ch, rot)); exit(0); } void usage() { fprintf(stderr,"usage: caesar [rotation]\n"); exit(1); }