[unix-history] / usr / 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
	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
4ae50aef RM	1	.TH CRYPT 1
	2	.SH NAME
	3	crypt \- encode/decode
	4	.SH SYNOPSIS
	5	.B crypt
	6	[ password ]
	7	.SH DESCRIPTION
	8	.I Crypt
	9	reads from the standard input and writes
	10	on the standard output.
	11	The
	12	.I password
	13	is a key that selects a particular transformation.
	14	If no
	15	.I password
	16	is given,
	17	.I crypt
	18	demands a key from the terminal and turns
	19	off printing while the key is being typed in.
	20	.I Crypt
	21	encrypts and decrypts with the same key:
	22	.PP
	23	crypt key <clear >cypher
	24	.br
	25	crypt key <cypher \| pr
	26	.PP
	27	will print the clear.
	28	.PP
	29	Files encrypted by
	30	.I crypt
	31	are compatible with those treated by the editor
	32	.I ed
	33	in encryption mode.
	34	.PP
	35	The security of encrypted files depends on three factors:
	36	the fundamental method must be hard to solve;
	37	direct search of the key space must be infeasible;
	38	`sneak paths' by which keys or cleartext can become
	39	visible must be minimized.
	40	.PP
	41	.I Crypt
	42	implements a one-rotor machine designed along the lines
	43	of the German Enigma, but with a 256-element rotor.
	44	Methods of attack on such machines are known, but not widely;
	45	moreover the amount of work required is likely to be large.
	46	.PP
	47	The transformation of a key into the internal
	48	settings of the machine is deliberately designed to
	49	be expensive, i.e. to take a substantial fraction of
	50	a second to compute.
	51	However,
	52	if keys are restricted to (say)
	53	three lower-case letters,
	54	then encrypted files can be read by expending only
	55	a substantial fraction of
	56	five minutes of machine time.
	57	.PP
	58	Since the key is an argument to the
	59	.I crypt
	60	command,
	61	it is potentially visible to users executing
	62	.IR ps (1)
	63	or a derivative.
	64	To minimize this possibility,
65	.I crypt
66	takes care to destroy any record of the key
67	immediately upon entry.
68	No doubt the choice of keys and key security
69	are the most vulnerable aspect of
70	.I crypt.
71	.SH FILES
72	/dev/tty for typed key
73	.SH "SEE ALSO"
74	ed(1),
75	makekey(8)
76	.SH BUGS
77	There is no warranty of merchantability nor any warranty
78	of fitness for a particular purpose nor any other warranty,
79	either express or implied, as to the accuracy of the
80	enclosed materials or as to their suitability for any
81	particular purpose. Accordingly, Bell Telephone
82	Laboratories assumes no responsibility for their use by the
83	recipient. Further, Bell Laboratories assumes no obligation
84	to furnish any assistance of any kind whatsoever, or to
85	furnish any additional information or documentation.