=pod =head1 NAME des - encrypt or decrypt data using Data Encryption Standard =head1 SYNOPSIS B ( B<-e> | B<-E> ) | ( B<-d> | B<-D> ) | ( B<->[B][B] ) | [ B<-b3hfs> ] [ B<-k> I ] ] [ B<-u>[I] [ I [ I ] ] =head1 NOTE This page describes the B stand-alone program, not the B command. =head1 DESCRIPTION B encrypts and decrypts data using the Data Encryption Standard algorithm. One of B<-e>, B<-E> (for encrypt) or B<-d>, B<-D> (for decrypt) must be specified. It is also possible to use B<-c> or B<-C> in conjunction or instead of the a encrypt/decrypt option to generate a 16 character hexadecimal checksum, generated via the I. Two standard encryption modes are supported by the B program, Cipher Block Chaining (the default) and Electronic Code Book (specified with B<-b>). The key used for the DES algorithm is obtained by prompting the user unless the B<-k> I option is given. If the key is an argument to the B command, it is potentially visible to users executing ps(1) or a derivative. To minimise this possibility, B takes care to destroy the key argument immediately upon entry. If your shell keeps a history file be careful to make sure it is not world readable. Since this program attempts to maintain compatibility with sunOS's des(1) command, there are 2 different methods used to convert the user supplied key to a des key. Whenever and one or more of B<-E>, B<-D>, B<-C> or B<-3> options are used, the key conversion procedure will not be compatible with the sunOS des(1) version but will use all the user supplied character to generate the des key. B command reads from standard input unless I is specified and writes to standard output unless I is given. =head1 OPTIONS =over 4 =item B<-b> Select ECB (eight bytes at a time) encryption mode. =item B<-3> Encrypt using triple encryption. By default triple cbc encryption is used but if the B<-b> option is used then triple ECB encryption is performed. If the key is less than 8 characters long, the flag has no effect. =item B<-e> Encrypt data using an 8 byte key in a manner compatible with sunOS des(1). =item B<-E> Encrypt data using a key of nearly unlimited length (1024 bytes). This will product a more secure encryption. =item B<-d> Decrypt data that was encrypted with the B<-e> option. =item B<-D> Decrypt data that was encrypted with the B<-E> option. =item B<-c> Generate a 16 character hexadecimal cbc checksum and output this to stderr. If a filename was specified after the B<-c> option, the checksum is output to that file. The checksum is generated using a key generated in a sunOS compatible manner. =item B<-C> A cbc checksum is generated in the same manner as described for the B<-c> option but the DES key is generated in the same manner as used for the B<-E> and B<-D> options =item B<-f> Does nothing - allowed for compatibility with sunOS des(1) command. =item B<-s> Does nothing - allowed for compatibility with sunOS des(1) command. =item B<-k> I Use the encryption I specified. =item B<-h> The I is assumed to be a 16 character hexadecimal number. If the B<-3> option is used the key is assumed to be a 32 character hexadecimal number. =item B<-u> This flag is used to read and write uuencoded files. If decrypting, the input file is assumed to contain uuencoded, DES encrypted data. If encrypting, the characters following the B<-u> are used as the name of the uuencoded file to embed in the begin line of the uuencoded output. If there is no name specified after the B<-u>, the name text.des will be embedded in the header. =back =head1 SEE ALSO ps(1), L =head1 BUGS The problem with using the B<-e> option is the short key length. It would be better to use a real 56-bit key rather than an ASCII-based 56-bit pattern. Knowing that the key was derived from ASCII radically reduces the time necessary for a brute-force cryptographic attack. My attempt to remove this problem is to add an alternative text-key to DES-key function. This alternative function (accessed via B<-E>, B<-D>, B<-S> and B<-3>) uses DES to help generate the key. Be carefully when using the B<-u> option. Doing B I will not decrypt filename (the B<-u> option will gobble the B<-d> option). The VMS operating system operates in a world where files are always a multiple of 512 bytes. This causes problems when encrypted data is send from Unix to VMS since a 88 byte file will suddenly be padded with 424 null bytes. To get around this problem, use the B<-u> option to uuencode the data before it is send to the VMS system. =head1 AUTHOR Eric Young (eay@cryptsoft.com) =cut