1=pod 2 3=head1 NAME 4 5openssl-dhparam, 6dhparam - DH parameter manipulation and generation 7 8=head1 SYNOPSIS 9 10B<openssl dhparam> 11[B<-help>] 12[B<-inform DER|PEM>] 13[B<-outform DER|PEM>] 14[B<-in> I<filename>] 15[B<-out> I<filename>] 16[B<-dsaparam>] 17[B<-check>] 18[B<-noout>] 19[B<-text>] 20[B<-C>] 21[B<-2>] 22[B<-5>] 23[B<-rand file...>] 24[B<-writerand file>] 25[B<-engine id>] 26[I<numbits>] 27 28=head1 DESCRIPTION 29 30This command is used to manipulate DH parameter files. 31 32=head1 OPTIONS 33 34=over 4 35 36=item B<-help> 37 38Print out a usage message. 39 40=item B<-inform DER|PEM> 41 42This specifies the input format. The B<DER> option uses an ASN1 DER encoded 43form compatible with the PKCS#3 DHparameter structure. The PEM form is the 44default format: it consists of the B<DER> format base64 encoded with 45additional header and footer lines. 46 47=item B<-outform DER|PEM> 48 49This specifies the output format, the options have the same meaning and default 50as the B<-inform> option. 51 52=item B<-in> I<filename> 53 54This specifies the input filename to read parameters from or standard input if 55this option is not specified. 56 57=item B<-out> I<filename> 58 59This specifies the output filename parameters to. Standard output is used 60if this option is not present. The output filename should B<not> be the same 61as the input filename. 62 63=item B<-dsaparam> 64 65If this option is used, DSA rather than DH parameters are read or created; 66they are converted to DH format. Otherwise, "strong" primes (such 67that (p-1)/2 is also prime) will be used for DH parameter generation. 68 69DH parameter generation with the B<-dsaparam> option is much faster, 70and the recommended exponent length is shorter, which makes DH key 71exchange more efficient. Beware that with such DSA-style DH 72parameters, a fresh DH key should be created for each use to 73avoid small-subgroup attacks that may be possible otherwise. 74 75=item B<-check> 76 77Performs numerous checks to see if the supplied parameters are valid and 78displays a warning if not. 79 80=item B<-2>, B<-5> 81 82The generator to use, either 2 or 5. If present then the 83input file is ignored and parameters are generated instead. If not 84present but B<numbits> is present, parameters are generated with the 85default generator 2. 86 87=item B<-rand file...> 88 89A file or files containing random data used to seed the random number 90generator. 91Multiple files can be specified separated by an OS-dependent character. 92The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 93all others. 94 95=item [B<-writerand file>] 96 97Writes random data to the specified I<file> upon exit. 98This can be used with a subsequent B<-rand> flag. 99 100=item I<numbits> 101 102This option specifies that a parameter set should be generated of size 103I<numbits>. It must be the last option. If this option is present then 104the input file is ignored and parameters are generated instead. If 105this option is not present but a generator (B<-2> or B<-5>) is 106present, parameters are generated with a default length of 2048 bits. 107 108=item B<-noout> 109 110This option inhibits the output of the encoded version of the parameters. 111 112=item B<-text> 113 114This option prints out the DH parameters in human readable form. 115 116=item B<-C> 117 118This option converts the parameters into C code. The parameters can then 119be loaded by calling the get_dhNNNN() function. 120 121=item B<-engine id> 122 123Specifying an engine (by its unique B<id> string) will cause B<dhparam> 124to attempt to obtain a functional reference to the specified engine, 125thus initialising it if needed. The engine will then be set as the default 126for all available algorithms. 127 128=back 129 130=head1 WARNINGS 131 132The program B<dhparam> combines the functionality of the programs B<dh> and 133B<gendh> in previous versions of OpenSSL. The B<dh> and B<gendh> 134programs are retained for now but may have different purposes in future 135versions of OpenSSL. 136 137=head1 NOTES 138 139PEM format DH parameters use the header and footer lines: 140 141 -----BEGIN DH PARAMETERS----- 142 -----END DH PARAMETERS----- 143 144OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42 145DH. 146 147This program manipulates DH parameters not keys. 148 149=head1 BUGS 150 151There should be a way to generate and manipulate DH keys. 152 153=head1 SEE ALSO 154 155L<dsaparam(1)> 156 157=head1 COPYRIGHT 158 159Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved. 160 161Licensed under the OpenSSL license (the "License"). You may not use 162this file except in compliance with the License. You can obtain a copy 163in the file LICENSE in the source distribution or at 164L<https://www.openssl.org/source/license.html>. 165 166=cut 167