OpenBSD-4.6/games/caesar/caesar.6

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.\"	@(#)caesar.6	8.2 (Berkeley) 11/16/93
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt CAESAR 6
.Os
.Sh NAME
.Nm caesar ,
.Nm rot13
.Nd decrypt caesar cyphers
.Sh SYNOPSIS
.Nm caesar
.Op Ar rotation
.Nm rot13
.Sh DESCRIPTION
The
.Nm
utility attempts to decrypt caesar cyphers 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
If this utility is invoked as
.Nm rot13 ,
it will rotate by 13 characters.
This format is commonly used on
.Tn USENET
and in some of the databases used by the
.Xr fortune 6
program to
.Dq disguise
their content.
.Pp
The frequency (from most common to least) of English letters is as follows:
.Bd -filled -offset indent
ETAONRISHDLFCMUGPYWBVKXJQZ
.Ed
.Pp
Their frequencies as a percentage are as follows:
.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