.\" This file is free software, distributed under the BSD license.
.Dd November 16, 1993
.Dt CAESAR 6
.Os
.Sh NAME
.Nm caesar ,
.Nm rot13
.Nd decrypt caesar ciphers
.Sh SYNOPSIS
.Nm
.Op Ar rotation
.Sh DESCRIPTION
The
.Nm
utility attempts to decrypt caesar ciphers using English letter frequency
statistics.
.Nm
reads from the standard input and writes to the standard output.
.Pp
The optional numerical argument
.Ar rotation
may be used to specify a specific rotation value.
.Pp
The frequency (from most common to least) of English letters is as follows:
.Pp
.Bd -filled -offset indent
ETAONRISHDLFCMUGPYWBVKXJQZ
.Ed
.Pp
Their frequencies as a percentage are as follows:
.Pp
.Bd -filled -offset indent
E(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),
D(3.8), L(3.4), F(2.9), C(2.7), M(2.5), U(2.4), G(2),
P(1.9), Y(1.9), W(1.5), B(1.4), V(.9), K(.4), X(.15), J(.13), Q(.11), Z(.07).
.Ed
.Pp
Rotated postings to
.Tn USENET
and some of the databases used by the
.Xr fortune 6
program are rotated by 13 characters.