2000-04-13 06:33:22 +00:00
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=pod
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=head1 NAME
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dhparam - DH parameter manipulation and generation
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=head1 SYNOPSIS
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B<openssl dhparam>
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[B<-inform DER|PEM>]
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[B<-outform DER|PEM>]
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[B<-in> I<filename>]
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[B<-out> I<filename>]
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[B<-dsaparam>]
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[B<-noout>]
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[B<-text>]
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[B<-C>]
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[B<-2>]
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[B<-5>]
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[B<-rand> I<file(s)>]
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[I<numbits>]
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=head1 DESCRIPTION
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This command is used to manipulate DH parameter files.
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=head1 OPTIONS
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=over 4
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=item B<-inform DER|PEM>
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This specifies the input format. The B<DER> option uses an ASN1 DER encoded
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form compatible with the PKCS#3 DHparameter structure. The PEM form is the
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default format: it consists of the B<DER> format base64 encoded with
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additional header and footer lines.
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=item B<-outform DER|PEM>
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This specifies the output format, the options have the same meaning as the
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B<-inform> option.
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=item B<-in> I<filename>
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This specifies the input filename to read parameters from or standard input if
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this option is not specified.
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=item B<-out> I<filename>
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This specifies the output filename parameters to. Standard output is used
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if this option is not present. The output filename should B<not> be the same
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as the input filename.
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=item B<-dsaparam>
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If this option is used, DSA rather than DH parameters are read or created;
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they are converted to DH format. Otherwise, "strong" primes (such
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that (p-1)/2 is also prime) will be used for DH parameter generation.
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DH parameter generation with the B<-dsaparam> option is much faster,
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and the recommended exponent length is shorter, which makes DH key
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exchange more efficient. Beware that with such DSA-style DH
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parameters, a fresh DH key should be created for each use to
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avoid small-subgroup attacks that may be possible otherwise.
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=item B<-2>, B<-5>
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The generator to use, either 2 or 5. 2 is the default. If present then the
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input file is ignored and parameters are generated instead.
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=item B<-rand> I<file(s)>
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a file or files containing random data used to seed the random number
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generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
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Multiple files can be specified separated by a OS-dependent character.
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2000-11-13 01:03:58 +00:00
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The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
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2000-04-13 06:33:22 +00:00
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all others.
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=item I<numbits>
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this option specifies that a parameter set should be generated of size
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I<numbits>. It must be the last option. If not present then a value of 512
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is used. If this option is present then the input file is ignored and
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parameters are generated instead.
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=item B<-noout>
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this option inhibits the output of the encoded version of the parameters.
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=item B<-text>
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this option prints out the DH parameters in human readable form.
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=item B<-C>
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this option converts the parameters into C code. The parameters can then
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be loaded by calling the B<get_dh>I<numbits>B<()> function.
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=back
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=head1 WARNINGS
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The program B<dhparam> combines the functionality of the programs B<dh> and
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B<gendh> in previous versions of OpenSSL and SSLeay. The B<dh> and B<gendh>
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programs are retained for now but may have different purposes in future
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versions of OpenSSL.
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=head1 NOTES
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PEM format DH parameters use the header and footer lines:
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-----BEGIN DH PARAMETERS-----
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-----END DH PARAMETERS-----
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OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42
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DH.
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This program manipulates DH parameters not keys.
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=head1 BUGS
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There should be a way to generate and manipulate DH keys.
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=head1 SEE ALSO
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L<dsaparam(1)|dsaparam(1)>
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=head1 HISTORY
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The B<dhparam> command was added in OpenSSL 0.9.5.
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The B<-dsaparam> option was added in OpenSSL 0.9.6.
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=cut
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