[unix-history] / usr / src / old / crypt / crypt.1

.\"	@(#)crypt.1	6.1 (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.
Commit	Line	Data
f93aeb97	1	.\" @(#)crypt.1 6.1 (Berkeley) %G%
c38495d9	2	.\"
f93aeb97	3	.TH CRYPT 1 ""
c38495d9 KM	4	.AT 3
	5	.SH NAME
	6	crypt \- encode/decode
	7	.SH SYNOPSIS
	8	.B crypt
	9	[ password ]
	10	.SH DESCRIPTION
	11	.I Crypt
	12	reads from the standard input and writes
	13	on the standard output.
	14	The
	15	.I password
	16	is a key that selects a particular transformation.
	17	If no
	18	.I password
	19	is given,
	20	.I crypt
	21	demands a key from the terminal and turns
	22	off printing while the key is being typed in.
	23	.I Crypt
	24	encrypts and decrypts with the same key:
	25	.PP
	26	crypt key <clear >cypher
	27	.br
	28	crypt key <cypher \| pr
	29	.PP
	30	will print the clear.
	31	.PP
	32	Files encrypted by
	33	.I crypt
	34	are compatible with those treated by the editor
	35	.I ed
	36	in encryption mode.
	37	.PP
	38	The security of encrypted files depends on three factors:
	39	the fundamental method must be hard to solve;
	40	direct search of the key space must be infeasible;
	41	`sneak paths' by which keys or cleartext can become
	42	visible must be minimized.
	43	.PP
	44	.I Crypt
	45	implements a one-rotor machine designed along the lines
	46	of the German Enigma, but with a 256-element rotor.
	47	Methods of attack on such machines are known, but not widely;
	48	moreover the amount of work required is likely to be large.
	49	.PP
	50	The transformation of a key into the internal
	51	settings of the machine is deliberately designed to
	52	be expensive, i.e. to take a substantial fraction of
	53	a second to compute.
	54	However,
	55	if keys are restricted to (say)
	56	three lower-case letters,
	57	then encrypted files can be read by expending only
	58	a substantial fraction of
	59	five minutes of machine time.
	60	.PP
	61	Since the key is an argument to the
	62	.I crypt
	63	command,
	64	it is potentially visible to users executing
	65	.IR ps (1)
	66	or a derivative.
	67	To minimize this possibility,
68	.I crypt
69	takes care to destroy any record of the key
70	immediately upon entry.
71	No doubt the choice of keys and key security
72	are the most vulnerable aspect of
73	.I crypt.
74	.SH FILES
75	/dev/tty for typed key
76	.SH "SEE ALSO"
77	ed(1),
78	makekey(8)
79	.SH BUGS
80	There is no warranty of merchantability nor any warranty
81	of fitness for a particular purpose nor any other warranty,
82	either express or implied, as to the accuracy of the
83	enclosed materials or as to their suitability for any
84	particular purpose. Accordingly, Bell Telephone
85	Laboratories assumes no responsibility for their use by the
86	recipient. Further, Bell Laboratories assumes no obligation
87	to furnish any assistance of any kind whatsoever, or to
88	furnish any additional information or documentation.