1.\" $OpenBSD: caesar.6,v 1.8 2007/05/31 19:19:17 jmc Exp $ 2.\" 3.\" Copyright (c) 1989, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)caesar.6 8.2 (Berkeley) 11/16/93 31.\" 32.Dd $Mdocdate: May 31 2007 $ 33.Dt CAESAR 6 34.Os 35.Sh NAME 36.Nm caesar , 37.Nm rot13 38.Nd decrypt caesar cyphers 39.Sh SYNOPSIS 40.Nm caesar 41.Op Ar rotation 42.Nm rot13 43.Sh DESCRIPTION 44The 45.Nm 46utility attempts to decrypt caesar cyphers using English letter frequency 47statistics. 48.Nm 49reads from the standard input and writes to the standard output. 50.Pp 51The optional numerical argument 52.Ar rotation 53may be used to specify a specific rotation value. 54.Pp 55If this utility is invoked as 56.Nm rot13 , 57it will rotate by 13 characters. 58This format is commonly used on 59.Tn USENET 60and in some of the databases used by the 61.Xr fortune 6 62program to 63.Dq disguise 64their content. 65.Pp 66The frequency (from most common to least) of English letters is as follows: 67.Bd -filled -offset indent 68ETAONRISHDLFCMUGPYWBVKXJQZ 69.Ed 70.Pp 71Their frequencies as a percentage are as follows: 72.Bd -filled -offset indent 73E(13), T(10.5), A(8.1), O(7.9), N(7.1), R(6.8), I(6.3), S(6.1), H(5.2), 74D(3.8), L(3.4), F(2.9), C(2.7), M(2.5), U(2.4), G(2), 75P(1.9), Y(1.9), 76W(1.5), B(1.4), V(.9), K(.4), X(.15), J(.13), Q(.11), Z(.07). 77.Ed 78