path: root/secure/usr.bin/bdes/bdes.1

.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Matt Bishop of Dartmouth College.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)bdes.1	8.1 (Berkeley) 6/29/93
.\" $FreeBSD$
.\"
.Dd June 29, 1993
.Dt BDES 1
.Os
.Sh NAME
.Nm bdes
.Nd "encrypt/decrypt using the Data Encryption Standard (DES)"
.Sh SYNOPSIS
.Nm
.Op Fl abdp
.Op Fl F Ar N
.Op Fl f Ar N
.Op Fl k Ar key
.Op Fl m Ar N
.Op Fl o Ar N
.Op Fl v Ar vector
.Sh DESCRIPTION
The
.Nm
utility implements all
.Tn DES
modes of operation described in
.%T "FIPS PUB 81" ,
including alternative cipher feedback mode and both authentication
modes.
The
.Nm
utility reads from the standard input
and writes to the standard output.
By default,
the input is encrypted
using cipher block chaining (CBC) mode.
Using the same key
for encryption and decryption
preserves plain text.
.Pp
All modes but the electronic code book (ECB) mode
require an initialization vector;
if none is supplied,
the zero vector is used.
If no
.Ar key
is specified on the command line,
the user is prompted for one (see
.Xr getpass 3
for more details).
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl a
The key and initialization vector strings
are to be taken as
.Tn ASCII ,
suppressing the special interpretation given to leading
.Dq Li 0X ,
.Dq Li 0x ,
.Dq Li 0B ,
and
.Dq Li 0b
characters.
This flag applies to
.Em both
the key and initialization vector.
.It Fl b
Use ECB mode.
.It Fl d
Decrypt the input.
.It Fl F Ar N
Use
.Ar N Ns \-bit
alternative CFB mode.
Currently
.Ar N
must be a multiple of 7
between 7 and 56 inclusive
(this does not conform to the alternative CFB mode specification).
.It Fl f Ar N
Use
.Ar N Ns \-bit
CFB mode.
Currently
.Ar N
must be a multiple of 8 between 8 and 64 inclusive (this does not conform
to the standard CFB mode specification).
.It Fl k Ar key
Use
.Ar key
as the cryptographic key.
.It Fl m Ar N
Compute a message authentication code (MAC) of
.Ar N
bits on the input.
The value of
.Ar N
must be between 1 and 64 inclusive; if
.Ar N
is not a multiple of 8,
enough 0 bits will be added
to pad the MAC length
to the nearest multiple of 8.
Only the MAC is output.
MACs are only available
in CBC mode
or in CFB mode.
.It Fl o Ar N
Use
.Ar N Ns \-bit
ouput feedback (OFB) mode.
Currently
.Ar N
must be a multiple of 8 between 8 and 64 inclusive (this does not conform
to the OFB mode specification).
.It Fl p
Disable the resetting of the parity bit.
This flag forces
the parity bit of the key
to be used as typed,
rather than making
each character be of odd parity.
It is used only if the key is given in
.Tn ASCII .
.It Fl v Ar vector
Set the initialization vector to
.Ar vector ;
the vector is interpreted in the same way as the key.
The vector is ignored in ECB mode.
.El
.Pp
The key and initialization vector
are taken as sequences of
.Tn ASCII
characters which are then mapped
into their bit representations.
If either begins with
.Dq Li 0X
or
.Dq Li 0x ,
that one is taken
as a sequence of hexadecimal digits
indicating the bit pattern;
if either begins with
.Dq Li 0B
or
.Dq Li 0b ,
that one is taken
as a sequence of binary digits
indicating the bit pattern.
In either case,
only the leading 64 bits
of the key or initialization vector
are used,
and if fewer than 64 bits are provided,
enough 0 bits are appended
to pad the key to 64 bits.
.Pp
According to the
.Tn DES
standard,
the low-order bit of each character
in the key string is deleted.
Since most
.Tn ASCII
representations
set the high-order bit to 0,
simply deleting the low-order bit
effectively reduces the size of the key space
from 2^56 to 2^48 keys.
To prevent this,
the high-order bit must be a function
depending in part upon the low-order bit;
so,
the high-order bit is set
to whatever value gives odd parity.
This preserves the key space size.
Note this resetting of the parity bit is
.Em not
done if the key
is given in binary or hex,
and can be disabled for
.Tn ASCII
keys as well.
.Pp
The
.Tn DES
is considered a very strong cryptosystem,
and other than table lookup attacks,
key search attacks,
and Hellman's time-memory tradeoff
(all of which are very expensive and time-consuming),
no cryptanalytic methods
for breaking the
.Tn DES
are known in the open literature.
No doubt the choice of keys
and key security
are the most vulnerable aspect of
.Nm .
.Sh IMPLEMENTATION NOTES
For implementors wishing to write
software compatible with this program,
the following notes are provided.
This software is believed
to be compatible with the implementation
of the data encryption standard
distributed by Sun Microsystems, Inc.
.Pp
In the ECB and CBC modes,
plaintext is encrypted in units of 64 bits
(8 bytes, also called a block).
To ensure that the plaintext file
is encrypted correctly,
.Nm
will (internally) append from 1 to 8 bytes,
the last byte containing an integer
stating how many bytes of that final block
are from the plaintext file,
and encrypt the resulting block.
Hence,
when decrypting,
the last block may contain from 0 to 7 characters
present in the plaintext file,
and the last byte tells how many.
Note that if during decryption
the last byte of the file
does not contain an integer between 0 and 7,
either the file has been corrupted
or an incorrect key has been given.
A similar mechanism is used
for the OFB and CFB modes,
except that those
simply require the length of the input
to be a multiple of the mode size,
and the final byte contains an integer
between 0 and one less than the number
of bytes being used as the mode.
(This was another reason
that the mode size must be
a multiple of 8 for those modes.)
.Pp
Unlike Sun's implementation,
unused bytes of that last block
are not filled with random data,
but instead contain
what was in those byte positions
in the preceding block.
This is quicker and more portable,
and does not weaken the encryption significantly.
.Pp
If the key is entered in
.Tn ASCII ,
the parity bits of the key characters
are set so that each key character
is of odd parity.
Unlike Sun's implementation,
it is possible to enter binary or hexadecimal
keys on the command line,
and if this is done,
the parity bits are
.Em not
reset.
This allows testing
using arbitrary bit patterns as keys.
.Pp
The Sun implementation
always uses an initialization vector of 0
(that is, all zeroes).
By default,
.Nm
does too,
but this may be changed
from the command line.
.Sh SEE ALSO
.Xr getpass 3
.Rs
.%T "Data Encryption Standard"
.%R "Federal Information Processing Standard #46"
.%Q "National Bureau of Standards, U.S. Department of Commerce, Washington DC"
.%D "January 1977"
.Re
.Rs
.%T "DES Modes of Operation"
.%R "Federal Information Processing Standard #81"
.%Q "National Bureau of Standards, U.S. Department of Commerce, Washington DC"
.%D "December 1980"
.Re
.Rs
.%A "Dorothy Denning"
.%B "Cryptography and Data Security"
.%Q "Addison-Wesley Publishing Co., Reading, MA"
.%D 1982
.Re
.Rs
.%A "Matt Bishop"
.%T "Implementation Notes on bdes(1)"
.%R "Technical Report PCS-TR-91-158"
.%Q "Department of Mathematics and Computer Science, Dartmouth College, Hanover, NH 03755"
.%D "April 1991"
.Re
.Sh DISCLAIMER
.Bd -literal
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
.Ed
.Sh BUGS
There is a controversy raging over whether the
.Tn DES
will still be secure
in a few years.
The advent of special-purpose hardware
could reduce the cost of any of the
methods of attack named above
so that they are no longer
computationally infeasible.
.Pp
As the key or key schedule
is stored in memory,
the encryption can be
compromised if memory is readable.
Additionally,
programs which display programs' arguments
may compromise the key and initialization vector,
if they are specified on the command line.
To avoid this
.Nm
overwrites its arguments,
however,
the obvious race
cannot currently be avoided.
.Pp
Certain specific keys
should be avoided
because they introduce
potential weaknesses;
these keys,
called the
.Em weak
and
.Em semiweak
keys, are (in hex notation, where
.Ar p
is either 0 or 1, and
.Ar P
is either
.Ql e
or
.Ql f ) :
.Bl -column "0x0p0p0p0p0p0p0p0p" -offset indent
.It "0x0p0p0p0p0p0p0p0p	0x0p1P0p1P0p0P0p0P"
.It "0x0pep0pep0pfp0pfp	0x0pfP0pfP0pfP0pfP"
.It "0x1P0p1P0p0P0p0P0p	0x1P1P1P1P0P0P0P0P"
.It "0x1Pep1Pep0Pfp0Pfp	0x1PfP1PfP0PfP0PfP"
.It "0xep0pep0pfp0pfp0p	0xep1Pep1pfp0Pfp0P"
.It "0xepepepepepepepep	0xepfPepfPfpfPfpfP"
.It "0xfP0pfP0pfP0pfP0p	0xfP1PfP1PfP0PfP0P"
.It "0xfPepfPepfPepfPep	0xfPfPfPfPfPfPfPfP"
.El
.Pp
This is inherent in the
.Tn DES
algorithm;
see
.Rs
.%A Moore
.%A Simmons
.%T "Cycle structure of the DES with weak and semi-weak keys"
.%B "Advances in Cryptology \- Crypto '86 Proceedings"
.%Q "Springer-Verlag New York"
.%D 1987
.%P "pp. 9-32"
.Re