manual page distributed with 4.1BSD

SCCS-vsn: old/crypt/crypt.1 4.1

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+.\"    @(#)crypt.1     4.1 (Berkeley) %G%
+.\"
+.TH CRYPT 1 
+.AT 3
+.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
+       crypt key <clear >cypher
+.br
+       crypt key <cypher | pr
+.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 cleartext 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.
+No doubt the choice of keys and key security
+are the most vulnerable aspect of
+.I crypt.
+.SH FILES
+/dev/tty for typed key
+.SH "SEE ALSO"
+ed(1),
+makekey(8)
+.SH BUGS
+There is no warranty of merchantability nor any warranty
+of fitness for a particular purpose nor any other warranty,
+either express or implied, as to the accuracy of the
+enclosed materials or as to their suitability for any
+particular purpose.  Accordingly, Bell Telephone
+Laboratories assumes no responsibility for their use by the
+recipient.   Further, Bell Laboratories assumes no obligation
+to furnish any assistance of any kind whatsoever, or to
+furnish any additional information or documentation.