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+=pod
+
+=head1 NAME
+
+dhparam - DH parameter manipulation and generation
+
+=head1 SYNOPSIS
+
+B<openssl dhparam>
+[B<-inform DER|PEM>]
+[B<-outform DER|PEM>]
+[B<-in> I<filename>]
+[B<-out> I<filename>]
+[B<-dsaparam>]
+[B<-noout>]
+[B<-text>]
+[B<-C>]
+[B<-2>]
+[B<-5>]
+[B<-rand> I<file(s)>]
+[B<-engine id>]
+[I<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> I<filename>
+
+This specifies the input filename to read parameters from or standard input if
+this option is not specified.
+
+=item B<-out> I<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<-dsaparam>
+
+If this option is used, DSA rather than DH parameters are read or created;
+they are converted to DH format.  Otherwise, "strong" primes (such
+that (p-1)/2 is also prime) will be used for DH parameter generation.
+
+DH parameter generation with the B<-dsaparam> option is much faster,
+and the recommended exponent length is shorter, which makes DH key
+exchange more efficient.  Beware that with such DSA-style DH
+parameters, a fresh DH key should be created for each use to
+avoid small-subgroup attacks that may be possible otherwise.
+
+=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> I<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 OpenVMS, and B<:> for
+all others.
+
+=item I<numbits>
+
+this option specifies that a parameter set should be generated of size
+I<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_dh>I<numbits>B<()> function.
+
+=item B<-engine id>
+
+specifying an engine (by it's unique B<id> string) will cause B<req>
+to attempt to obtain a functional reference to the specified engine,
+thus initialising it if needed. The engine will then be set as the default
+for all available algorithms.
+
+=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)>
+
+=head1 HISTORY
+
+The B<dhparam> command was added in OpenSSL 0.9.5.
+The B<-dsaparam> option was added in OpenSSL 0.9.6.
+
+=cut