587481e04a
one man page, not section eight. This is the first round of such changes and only fixes man pages in manual section one.
305 lines
11 KiB
Groff
305 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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.\"
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.TH BDES 1 "June 29, 1993"
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.UC 6
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.SH NAME
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bdes \- encrypt/decrypt using the Data Encryption Standard
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.SH SYNOPSIS
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.nf
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.ft B
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bdes [ \-abdp ] [ \-F N ] [ \-f N ] [ \-k key ]
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.ti +5
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[ \-m N ] [ \-o N ] [ \-v vector ]
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.ft R
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.fi
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.SH DESCRIPTION
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.I Bdes
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implements all DES modes of operation described in FIPS PUB 81,
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including alternative cipher feedback mode and both authentication
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modes.
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.I 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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.I key
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is specified on the command line, the user is prompted for one (see
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.IR 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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.TP
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\-a
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The key and initialization vector strings are to be taken as ASCII,
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suppressing the special interpretation given to leading ``0X'', ``0x'',
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``0B'', and ``0b'' characters.
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This flag applies to
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.I both
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the key and initialization vector.
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.TP
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\-b
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Use electronic code book mode.
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.TP
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\-d
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Decrypt the input.
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.TP
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\-F
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Use
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.IR N -bit
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alternative cipher feedback mode.
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Currently
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.I 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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.TP
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\-f
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Use
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.IR N -bit
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cipher feedback mode.
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Currently
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.I 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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.TP
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\-k
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Use
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.I key
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as the cryptographic key.
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.TP
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\-m
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Compute a message authentication code (MAC) of
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.I N
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bits on the input.
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The value of
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.I N
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must be between 1 and 64 inclusive; if
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.I 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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.TP
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\-o
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Use
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.IR N -bit
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output feedback mode.
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Currently
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.I 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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.TP
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\-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 ASCII.
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.TP
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\-v
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Set the initialization vector to
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.IR 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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.PP
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The key and initialization vector are taken as sequences of ASCII
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characters which are then mapped into their bit representations.
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If either begins with ``0X'' or ``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 ``0B'' or ``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 DES standard, the low-order bit of each character in the
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key string is deleted.
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Since most ASCII 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\u\s-356\s0\d to 2\u\s-348\s0\d 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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.I not
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done if the key is given in binary or hex, and can be disabled for ASCII
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keys as well.
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.PP
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The DES 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 DES 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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.IR bdes .
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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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.I bdes
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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 ASCII, 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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.I 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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.I bdes
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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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crypt(3), getpass(3)
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.sp
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.IR "Data Encryption Standard" ,
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Federal Information Processing Standard #46,
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National Bureau of Standards,
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U.S. Department of Commerce,
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Washington DC
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(Jan. 1977)
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.sp
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.IR "DES Modes of Operation" ,
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Federal Information Processing Standard #81,
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National Bureau of Standards,
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U.S. Department of Commerce
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Washington DC
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(Dec. 1980)
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.sp
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Dorothy Denning,
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.IR "Cryptography and Data Security" ,
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Addison-Wesley Publishing Co.,
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Reading, MA
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\(co1982.
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.sp
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Matt Bishop,
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.IR "Implementation Notes on bdes(1)" ,
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Technical Report PCS-TR-91-158,
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Department of Mathematics and Computer Science,
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Dartmouth College,
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Hanover, NH 03755
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(Apr. 1991).
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.SH DISCLAIMER
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.nf
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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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.fi
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.SH BUGS
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There is a controversy raging over whether the DES 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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.I bdes
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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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.I weak
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and
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.I semiweak
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keys, are (in hex notation, where p is either 0 or 1, and P is either
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e or f):
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.sp
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.nf
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.in +10n
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.ta \w'0x0p0p0p0p0p0p0p0p\0\0\0'u+5n
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0x0p0p0p0p0p0p0p0p 0x0p1P0p1P0p0P0p0P
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0x0pep0pep0pfp0pfp 0x0pfP0pfP0pfP0pfP
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0x1P0p1P0p0P0p0P0p 0x1P1P1P1P0P0P0P0P
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0x1Pep1Pep0Pfp0Pfp 0x1PfP1PfP0PfP0PfP
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0xep0pep0pfp0pfp0p 0xep1Pep1pfp0Pfp0P
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0xepepepepepepepep 0xepfPepfPfpfPfpfP
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0xfP0pfP0pfP0pfP0p 0xfP1PfP1PfP0PfP0P
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0xfPepfPepfPepfPep 0xfPfPfPfPfPfPfPfP
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.fi
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.in -10n
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.sp
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This is inherent in the DES algorithm (see Moore and Simmons,
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\*(LqCycle structure of the DES with weak and semi-weak keys,\*(Rq
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.I "Advances in Cryptology \- Crypto '86 Proceedings" ,
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Springer-Verlag New York, \(co1987, pp. 9-32.)
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