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lib/des/des.man
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lib/des/des.man
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.TH DES 1
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.SH NAME
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des - encrypt or decrypt data using Data Encryption Standard
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.SH SYNOPSIS
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.B des
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(
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.B \-e
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.B \-E
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) | (
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.B \-d
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.B \-D
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) | (
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.B \-\fR[\fPcC\fR][\fPckname\fR]\fP
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) |
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[
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.B \-b3hfs
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] [
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.B \-k
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.I key
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]
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] [
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.B \-u\fR[\fIuuname\fR]
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[
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.I input-file
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[
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.I output-file
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] ]
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.SH DESCRIPTION
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.B des
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encrypts and decrypts data using the
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Data Encryption Standard algorithm.
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One of
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.B \-e, \-E
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(for encrypt) or
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.B \-d, \-D
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(for decrypt) must be specified.
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It is also possible to use
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.B \-c
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or
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.B \-C
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in conjunction or instead of the a encrypt/decrypt option to generate
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a 16 character hexadecimal checksum, generated via the
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.I des_cbc_cksum.
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.LP
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Two standard encryption modes are supported by the
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.B des
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program, Cipher Block Chaining (the default) and Electronic Code Book
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(specified with
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.B \-b
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).
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.LP
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The key used for the DES
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algorithm is obtained by prompting the user unless the
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.B `\-k
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.I key'
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option is given.
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If the key is an argument to the
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.B des
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command, it is potentially visible to users executing
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.BR ps (1)
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or a derivative. To minimise this possibility,
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.B des
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takes care to destroy the key argument immediately upon entry.
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If your shell keeps a history file be careful to make sure it is not
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world readable.
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.LP
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Since this program attempts to maintain compatability with sunOS's
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des(1) command, there are 2 different methods used to convert the user
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supplied key to a des key.
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Whenever and one or more of
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.B \-E, \-D, \-C
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or
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.B \-3
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options are used, the key conversion procedure will not be compatible
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with the sunOS des(1) version but will use all the user supplied
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character to generate the des key.
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.B des
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command reads from standard input unless
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.I input-file
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is specified and writes to standard output unless
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.I output-file
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is given.
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.SH OPTIONS
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.TP
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.B \-b
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Select ECB
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(eight bytes at a time) encryption mode.
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.TP
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.B \-3
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Encrypt using triple encryption.
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By default triple cbc encryption is used but if the
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.B \-b
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option is used then triple ecb encryption is performed.
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If the key is less than 8 characters long, the flag has no effect.
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.TP
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.B \-e
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Encrypt data using an 8 byte key in a manner compatible with sunOS
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des(1).
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.TP
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.B \-E
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Encrypt data using a key of nearly unlimited length (1024 bytes).
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This will product a more secure encryption.
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.TP
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.B \-d
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Decrypt data that was encrypted with the \-e option.
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.TP
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.B \-D
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Decrypt data that was encrypted with the \-E option.
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.TP
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.B \-c
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Generate a 16 character hexadecimal cbc checksum and output this to
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stderr.
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If a filename was specified after the
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.B \-c
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option, the checksum is output to that file.
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The checksum is generated using a key generated in a sunOS compatible
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manner.
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.TP
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.B \-C
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A cbc checksum is generated in the same manner as described for the
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.B \-c
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option but the DES key is generated in the same manner as used for the
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.B \-E
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and
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.B \-D
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options
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.TP
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.B \-f
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Does nothing - allowed for compatibility with sunOS des(1) command.
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.TP
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.B \-s
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Does nothing - allowed for compatibility with sunOS des(1) command.
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.TP
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.B "\-k \fIkey\fP"
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Use the encryption
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.I key
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specified.
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.TP
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.B "\-h"
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The
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.I key
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is assumed to be a 16 character hexadecimal number.
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If the
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.B "\-3"
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option is used the key is assumed to be a 32 character hexadecimal
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number.
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.TP
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.B \-u
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This flag is used to read and write uuencoded files. If decrypting,
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the input file is assumed to contain uuencoded, DES encrypted data.
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If encrypting, the characters following the -u are used as the name of
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the uuencoded file to embed in the begin line of the uuencoded
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output. If there is no name specified after the -u, the name text.des
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will be embedded in the header.
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.SH SEE ALSO
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.B ps (1)
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.B des_crypt(3)
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.SH BUGS
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.LP
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The problem with using the
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.B -e
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option is the short key length.
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It would be better to use a real 56-bit key rather than an
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ASCII-based 56-bit pattern. Knowing that the key was derived from ASCII
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radically reduces the time necessary for a brute-force cryptographic attack.
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My attempt to remove this problem is to add an alternative text-key to
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DES-key function. This alternative function (accessed via
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.B -E, -D, -S
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and
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.B -3
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)
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uses DES to help generate the key.
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.LP
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Be carefully when using the -u option. Doing des -ud <filename> will
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not decrypt filename (the -u option will gobble the d option).
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.LP
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The VMS operating system operates in a world where files are always a
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multiple of 512 bytes. This causes problems when encrypted data is
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send from unix to VMS since a 88 byte file will suddenly be padded
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with 424 null bytes. To get around this problem, use the -u option
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to uuencode the data before it is send to the VMS system.
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.SH AUTHOR
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.LP
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Eric Young (eay@psych.psy.uq.oz.au), Psychology Department,
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University of Queensland, Australia.
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