167 lines
4.4 KiB
Plaintext
167 lines
4.4 KiB
Plaintext
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=pod
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=head1 NAME
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openssl-dhparam,
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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<-help>]
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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<-check>]
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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 file...>]
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[B<-writerand file>]
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[B<-engine id>]
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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<-help>
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Print out a usage message.
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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 and default
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as the 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<-check>
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Performs numerous checks to see if the supplied parameters are valid and
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displays a warning if not.
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=item B<-2>, B<-5>
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The generator to use, either 2 or 5. If present then the
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input file is ignored and parameters are generated instead. If not
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present but B<numbits> is present, parameters are generated with the
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default generator 2.
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=item B<-rand file...>
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A file or files containing random data used to seed the random number
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generator.
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Multiple files can be specified separated by an OS-dependent character.
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The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
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all others.
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=item [B<-writerand file>]
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Writes random data to the specified I<file> upon exit.
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This can be used with a subsequent B<-rand> flag.
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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 this option is present then
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the input file is ignored and parameters are generated instead. If
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this option is not present but a generator (B<-2> or B<-5>) is
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present, parameters are generated with a default length of 2048 bits.
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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 get_dhNNNN() function.
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=item B<-engine id>
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Specifying an engine (by its unique B<id> string) will cause B<dhparam>
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to attempt to obtain a functional reference to the specified engine,
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thus initialising it if needed. The engine will then be set as the default
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for all available algorithms.
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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. 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)>
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=head1 COPYRIGHT
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Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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