416 lines
11 KiB
Groff
416 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 (DES)"
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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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The
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.Nm
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utility 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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The
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.Nm
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utility reads from the standard input
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and writes to the standard output.
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By default,
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the input is encrypted
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using cipher block chaining (CBC) mode.
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Using the same key
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for encryption and decryption
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preserves plain text.
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.Pp
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All modes but the electronic code book (ECB) mode
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require an initialization vector;
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if none is supplied,
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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,
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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
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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 ECB 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 CFB mode.
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Currently
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.Ar N
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must be a multiple of 7
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between 7 and 56 inclusive
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(this does not conform 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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CFB 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,
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enough 0 bits will be added
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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
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in CBC mode
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or in CFB 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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ouput feedback (OFB) 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
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the parity bit of the key
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to be used as typed,
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rather than making
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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 ECB mode.
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.El
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.Pp
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The key and initialization vector
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are taken as sequences of
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.Tn ASCII
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characters which are then mapped
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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
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as a sequence of hexadecimal digits
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indicating the 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
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as a sequence of binary digits
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indicating the bit pattern.
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In either case,
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only the leading 64 bits
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of the key or initialization vector
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are used,
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and if fewer than 64 bits are provided,
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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,
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the low-order bit of each character
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in the key string is deleted.
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Since most
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.Tn ASCII
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representations
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set the high-order bit to 0,
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simply deleting the low-order bit
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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,
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the high-order bit must be a function
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depending in part upon the low-order bit;
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so,
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the high-order bit is set
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to whatever value 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
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is given in binary or hex,
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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,
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and other than table lookup attacks,
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key search attacks,
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and Hellman's time-memory tradeoff
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(all of which are very expensive and time-consuming),
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no cryptanalytic methods
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for breaking 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
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and key security
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are the most vulnerable aspect of
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.Nm .
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.Sh IMPLEMENTATION NOTES
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For implementors wishing to write
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software compatible with this program,
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the following notes are provided.
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This software is believed
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to be compatible with the implementation
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of the data encryption standard
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distributed by Sun Microsystems, Inc.
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.Pp
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In the ECB and CBC modes,
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plaintext is encrypted in units of 64 bits
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(8 bytes, also called a block).
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To ensure that the plaintext file
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is encrypted correctly,
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.Nm
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will (internally) append from 1 to 8 bytes,
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the last byte containing an integer
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stating how many bytes of that final block
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are from the plaintext file,
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and encrypt the resulting block.
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Hence,
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when decrypting,
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the last block may contain from 0 to 7 characters
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present in the plaintext file,
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and the last byte tells how many.
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Note that if during decryption
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the last byte of the file
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does not contain an integer between 0 and 7,
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either the file has been corrupted
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or an incorrect key has been given.
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A similar mechanism is used
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for the OFB and CFB modes,
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except that those
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simply require the length of the input
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to be a multiple of the mode size,
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and the final byte contains an integer
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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
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that the mode size must be
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a multiple of 8 for those modes.)
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.Pp
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Unlike Sun's implementation,
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unused bytes of that last block
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are not filled with random data,
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but instead contain
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what was in those byte positions
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in the preceding block.
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This is quicker and more portable,
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and does not weaken the encryption 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
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are set so that each key character
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is of odd parity.
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Unlike Sun's implementation,
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it is possible to enter binary or hexadecimal
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keys on the command line,
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and if this is done,
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the parity bits are
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.Em not
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reset.
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This allows testing
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using arbitrary bit patterns as keys.
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.Pp
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The Sun implementation
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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,
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but this may be changed
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from the command line.
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.Sh SEE ALSO
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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
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could reduce the cost of any of the
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methods of attack named above
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so that they are no longer
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computationally infeasible.
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.Pp
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As the key or key schedule
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is stored in memory,
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the encryption can be
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compromised if memory is readable.
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Additionally,
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programs which display programs' arguments
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may compromise the key and initialization vector,
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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,
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however,
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the obvious race
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cannot currently be avoided.
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.Pp
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Certain specific keys
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should be avoided
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because they introduce
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potential weaknesses;
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these keys,
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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;
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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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