session-android/jni/openssl/crypto/des/des.pod

=pod

=head1 NAME

des - encrypt or decrypt data using Data Encryption Standard

=head1 SYNOPSIS

B<des>
(
B<-e>
|
B<-E>
) | (
B<-d>
|
B<-D>
) | (
B<->[B<cC>][B<ckname>]
) |
[
B<-b3hfs>
] [
B<-k>
I<key>
]
] [
B<-u>[I<uuname>]
[
I<input-file>
[
I<output-file>
] ]

=head1 NOTE

This page describes the B<des> stand-alone program, not the B<openssl des>
command.

=head1 DESCRIPTION

B<des>
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<des_cbc_cksum>.

Two standard encryption modes are supported by the
B<des>
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<key>
option is given.
If the key is an argument to the
B<des>
command, it is potentially visible to users executing
ps(1)
or a derivative.  To minimise this possibility,
B<des>
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<des>
command reads from standard input unless
I<input-file>
is specified and writes to standard output unless
I<output-file>
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<key>

Use the encryption 
I<key>
specified.

=item B<-h>

The
I<key>
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.

=head1 SEE ALSO

ps(1),
L<des_crypt(3)|des_crypt(3)>

=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<des -ud> I<filename> 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