openssl/doc/apps/dhparam.pod

=pod

=head1 NAME

dhparam - DH parameter manipulation and generation

=head1 SYNOPSIS

B<openssl dh>
[B<-inform DER|PEM>]
[B<-outform DER|PEM>]
[B<-in filename>]
[B<-out filename>]
[B<-noout>]
[B<-text>]
[B<-C>]
[B<-2>]
[B<-5>]
[B<-rand file(s)>]
[numbits]

=head1 DESCRIPTION

This command is used to manipulate DH parameter files.

=head1 OPTIONS

=over 4

=item B<-inform DER|PEM>

This specifies the input format. The B<DER> option uses an ASN1 DER encoded
form compatible with the PKCS#3 DHparameter structure. The PEM form is the
default format: it consists of the B<DER> format base64 encoded with
additional header and footer lines.

=item B<-outform DER|PEM>

This specifies the output format, the options have the same meaning as the 
B<-inform> option.

=item B<-in filename>

This specifies the input filename to read parameters from or standard input if
this option is not specified.

=item B<-out filename>

This specifies the output filename parameters to. Standard output is used
if this option is not present. The output filename should B<not> be the same
as the input filename.

=item B<-2>, B<-5>

The generator to use, either 2 or 5. 2 is the default. If present then the
input file is ignored and parameters are generated instead.

=item B<-rand file(s)>

a file or files containing random data used to seed the random number
generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
Multiple files can be specified separated by a OS-dependent character.
The separator is B<;> for MS-Windows, B<,> for OpenVSM, and B<:> for
all others.

=item B<numbits>

this option specifies that a parameter set should be generated of size
B<numbits>. It must be the last option. If not present then a value of 512
is used. If this option is present then the input file is ignored and 
parameters are generated instead.

=item B<-noout>

this option inhibits the output of the encoded version of the parameters.

=item B<-text>

this option prints out the DH parameters in human readable form.

=item B<-C>

this option converts the parameters into C code. The parameters can then
be loaded by calling the B<get_dhXXX()> function.

=back

=head1 WARNINGS

The program B<dhparam> combines the functionality of the programs B<dh> and
B<gendh> in previous versions of OpenSSL and SSLeay. The B<dh> and B<gendh>
programs are retained for now but may have different purposes in future 
versions of OpenSSL.

=head1 NOTES

PEM format DH parameters use the header and footer lines:

 -----BEGIN DH PARAMETERS-----
 -----END DH PARAMETERS-----

OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42
DH.

This program manipulates DH parameters not keys.

=head1 BUGS

There should be a way to generate and manipulate DH keys.

=head1 SEE ALSO

L<dsaparam(1)|dsaparam(1)>

=cut