SysIII/usr/src/man/man1/crypt.1

.TH CRYPT 1
.SH NAME
crypt \- encode/decode
.SH SYNOPSIS
.B crypt
[ password ]
.SH DESCRIPTION
.I Crypt\^
reads from the standard input and writes
on the standard output.
The
.I password\^
is a key that selects a particular transformation.
If no
.I password\^
is given,
.I crypt\^
demands a key from the terminal and turns
off printing while the key is being typed in.
.I Crypt\^
encrypts and decrypts with the same key:
.PP
.RS
crypt \|key \|<clear \|>cypher
.br
crypt \|key \|<cypher \|\(bv \|pr
.RE
.PP
will print the clear.
.PP
Files encrypted by
.I crypt\^
are compatible with those treated by the editor
.I ed\^
in encryption mode.
.PP
The security of encrypted files depends on three factors:
the fundamental method must be hard to solve;
direct search of the key space must be infeasible;
``sneak paths'' by which keys or clear text can become
visible must be minimized.
.PP
.I Crypt\^
implements a one-rotor machine designed along the lines
of the German Enigma, but with a 256-element rotor.
Methods of attack on such machines are known, but not widely;
moreover the amount of work required is likely to be large.
.PP
The transformation of a key into the internal
settings of the machine is deliberately designed to
be expensive, i.e. to take a substantial fraction of
a second to compute.
However,
if keys are restricted to (say)
three lower-case letters,
then encrypted files can be read by expending only
a substantial fraction of
five minutes of machine time.
.PP
Since the key is an argument to the
.I crypt\^
command,
it is potentially visible to users executing
.IR ps (1)
or a derivative.
To minimize this possibility,
.I crypt\^
takes care to destroy any record of the key
immediately upon entry.
The choice of keys and key security
are the most vulnerable aspect of
.IR crypt .
.SH FILES
.ta 1i
/dev/tty	for typed key
.DT
.SH SEE ALSO
ed(1),
makekey(8).
.SH BUGS
If output is piped to
.IR nroff (1)
and the encryption key is
.I not\^
given on the command line,
.I crypt\^
can leave terminal modes in a strange state
(see
.IR stty (1)).