mirror of
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218 lines
4.7 KiB
Plaintext
218 lines
4.7 KiB
Plaintext
=pod
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=head1 NAME
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des - encrypt or decrypt data using Data Encryption Standard
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=head1 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<->[B<cC>][B<ckname>]
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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>[I<uuname>]
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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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=head1 NOTE
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This page describes the B<des> stand-alone program, not the B<openssl des>
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command.
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=head1 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>, B<-E>
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(for encrypt) or
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B<-d>, B<-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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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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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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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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Since this program attempts to maintain compatibility 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>, B<-D>, B<-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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=head1 OPTIONS
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=over 4
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=item B<-b>
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Select ECB
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(eight bytes at a time) encryption mode.
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=item 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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=item 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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=item 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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=item B<-d>
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Decrypt data that was encrypted with the B<-e> option.
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=item B<-D>
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Decrypt data that was encrypted with the B<-E> option.
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=item 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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=item 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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=item B<-f>
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Does nothing - allowed for compatibility with sunOS des(1) command.
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=item B<-s>
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Does nothing - allowed for compatibility with sunOS des(1) command.
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=item B<-k> I<key>
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Use the encryption
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I<key>
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specified.
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=item 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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=item 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 B<-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 B<-u>, the name text.des
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will be embedded in the header.
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=head1 SEE ALSO
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ps(1),
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L<des_crypt(3)|des_crypt(3)>
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=head1 BUGS
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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>, B<-D>, B<-S>
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and
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B<-3>)
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uses DES to help generate the key.
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Be carefully when using the B<-u> option. Doing B<des -ud> I<filename> will
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not decrypt filename (the B<-u> option will gobble the B<-d> option).
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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 B<-u> option
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to uuencode the data before it is send to the VMS system.
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=head1 AUTHOR
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Eric Young (eay@cryptsoft.com)
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=cut
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