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