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BDES(1)			  BSD General Commands Manual		       BDES(1)

NAME
     bdes — encrypt/decrypt using the Data Encryption Standard (DES)

SYNOPSIS
     bdes [-abdp] [-F N] [-f N] [-k key] [-m N] [-o N] [-v vector]

DESCRIPTION
     The bdes utility implements all DES modes of operation described in FIPS
     PUB 81, including alternative cipher feedback mode and both authentica‐
     tion modes.  The bdes 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 decryp‐
     tion preserves plain text.

     All modes but the electronic code book (ECB) mode require an initializa‐
     tion vector; if none is supplied, the zero vector is used.	 If no key is
     specified on the command line, the user is prompted for one (see
     getpass(3) for more details).

     The options are as follows:

     -a	     The key and initialization vector strings are to be taken as
	     ASCII, suppressing the special interpretation given to leading
	     “0X”, “0x”, “0B”, and “0b” characters.  This flag applies to both
	     the key and initialization vector.

     -b	     Use ECB mode.

     -d	     Decrypt the input.

     -F N    Use N-bit alternative CFB mode.  Currently N must be a multiple
	     of 7 between 7 and 56 inclusive (this does not conform to the
	     alternative CFB mode specification).

     -f N    Use N-bit CFB mode.  Currently N must be a multiple of 8 between
	     8 and 64 inclusive (this does not conform to the standard CFB
	     mode specification).

     -k key  Use key as the cryptographic key.

     -m N    Compute a message authentication code (MAC) of N bits on the
	     input.  The value of N must be between 1 and 64 inclusive; if 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.

     -o N    Use N-bit ouput feedback (OFB) mode.  Currently N must be a mul‐
	     tiple of 8 between 8 and 64 inclusive (this does not conform to
	     the OFB mode specification).

     -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 ASCII.

     -v vector
	     Set the initialization vector to vector; the vector is inter‐
	     preted in the same way as the key.	 The vector is ignored in ECB
	     mode.

     The key and initialization vector are taken as sequences of ASCII charac‐
     ters which are then mapped into their bit representations.	 If either
     begins with “0X” or “0x”, that one is taken as a sequence of hexadecimal
     digits indicating the bit pattern; if either begins with “0B” or “0b”,
     that one is taken as a sequence of binary digits indicating the bit pat‐
     tern.  In either case, only the leading 64 bits of the key or initializa‐
     tion vector are used, and if fewer than 64 bits are provided, enough 0
     bits are appended to pad the key to 64 bits.

     According to the DES standard, the low-order bit of each character in the
     key string is deleted.  Since most 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
     not done if the key is given in binary or hex, and can be disabled for
     ASCII keys as well.

     The 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 DES are known in the open literature.  No doubt
     the choice of keys and key security are the most vulnerable aspect of
     bdes.

IMPLEMENTATION NOTES
     For implementors wishing to write software compatible with this program,
     the following notes are provided.	This software is believed to be com‐
     patible with the implementation of the data encryption standard distrib‐
     uted by Sun Microsystems, Inc.

     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, bdes 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 incor‐
     rect 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.)

     Unlike Sun's implementation, unused bytes of that last block are not
     filled with random data, but instead contain what was in those byte posi‐
     tions in the preceding block.  This is quicker and more portable, and
     does not weaken the encryption significantly.

     If the key is entered in ASCII, the parity bits of the key characters are
     set so that each key character is of odd parity.  Unlike Sun's implemen‐
     tation, it is possible to enter binary or hexadecimal keys on the command
     line, and if this is done, the parity bits are not reset.	This allows
     testing using arbitrary bit patterns as keys.

     The Sun implementation always uses an initialization vector of 0 (that
     is, all zeroes).  By default, bdes does too, but this may be changed from
     the command line.

SEE ALSO
     getpass(3)

     Data Encryption Standard, Federal Information Processing Standard #46,
     National Bureau of Standards, U.S. Department of Commerce, Washington DC,
     January 1977.

     DES Modes of Operation, Federal Information Processing Standard #81,
     National Bureau of Standards, U.S. Department of Commerce, Washington DC,
     December 1980.

     Dorothy Denning, Cryptography and Data Security, Addison-Wesley
     Publishing Co., Reading, MA, 1982.

     Matt Bishop, Implementation Notes on bdes(1), Technical Report PCS-
     TR-91-158, Department of Mathematics and Computer Science, Dartmouth
     College, Hanover, NH 03755, April 1991.

DISCLAIMER
     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.

BUGS
     There is a controversy raging over whether the 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.

     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 bdes overwrites
     its arguments, however, the obvious race cannot currently be avoided.

     Certain specific keys should be avoided because they introduce potential
     weaknesses; these keys, called the weak and semiweak keys, are (in hex
     notation, where p is either 0 or 1, and P is either ‘e’ or ‘f’):

	   0x0p0p0p0p0p0p0p0p	 0x0p1P0p1P0p0P0p0P
	   0x0pep0pep0pfp0pfp	 0x0pfP0pfP0pfP0pfP
	   0x1P0p1P0p0P0p0P0p	 0x1P1P1P1P0P0P0P0P
	   0x1Pep1Pep0Pfp0Pfp	 0x1PfP1PfP0PfP0PfP
	   0xep0pep0pfp0pfp0p	 0xep1Pep1pfp0Pfp0P
	   0xepepepepepepepep	 0xepfPepfPfpfPfpfP
	   0xfP0pfP0pfP0pfP0p	 0xfP1PfP1PfP0PfP0P
	   0xfPepfPepfPepfPep	 0xfPfPfPfPfPfPfPfP

     This is inherent in the DES algorithm; see Moore and Simmons, "Cycle
     structure of the DES with weak and semi-weak keys", Advances in
     Cryptology - Crypto '86 Proceedings, pp. 9-32, Springer-Verlag New York,
     1987.

BSD				 June 29, 1993				   BSD
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