doc/man1/openssl-dhparam.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 openssl-dhparam - DH parameter manipulation and generation
   6
   7 =head1 SYNOPSIS
   8
   9 B<openssl dhparam>
  10 [B<-help>]
  11 [B<-inform> B<DER>|B<PEM>]
  12 [B<-outform> B<DER>|B<PEM>]
  13 [B<-in> I<filename>]
  14 [B<-out> I<filename>]
  15 [B<-dsaparam>]
  16 [B<-check>]
  17 [B<-noout>]
  18 [B<-text>]
  19 [B<-C>]
  20 [B<-2>]
  21 [B<-3>]
  22 [B<-5>]
  23 [B<-rand> I<files>]
  24 [B<-writerand> I<file>]
  25 [B<-engine> I<id>]
  26 [I<numbits>]
  27
  28 =for openssl ifdef dsaparam engine
  29
  30 =head1 DESCRIPTION
  31
  32 This command is used to manipulate DH parameter files.
  33
  34 =head1 OPTIONS
  35
  36 =over 4
  37
  38 =item B<-help>
  39
  40 Print out a usage message.
  41
  42 =item B<-inform> B<DER>|B<PEM>
  43
  44 This specifies the input format. The B<DER> option uses an ASN1 DER encoded
  45 form compatible with the PKCS#3 DHparameter structure. The PEM form is the
  46 default format: it consists of the B<DER> format base64 encoded with
  47 additional header and footer lines.
  48
  49 =item B<-outform> B<DER>|B<PEM>
  50
  51 This specifies the output format, the options have the same meaning and default
  52 as the B<-inform> option.
  53
  54 =item B<-in> I<filename>
  55
  56 This specifies the input filename to read parameters from or standard input if
  57 this option is not specified.
  58
  59 =item B<-out> I<filename>
  60
  61 This specifies the output filename parameters to. Standard output is used
  62 if this option is not present. The output filename should B<not> be the same
  63 as the input filename.
  64
  65 =item B<-dsaparam>
  66
  67 If this option is used, DSA rather than DH parameters are read or created;
  68 they are converted to DH format.  Otherwise, "strong" primes (such
  69 that (p-1)/2 is also prime) will be used for DH parameter generation.
  70
  71 DH parameter generation with the B<-dsaparam> option is much faster,
  72 and the recommended exponent length is shorter, which makes DH key
  73 exchange more efficient.  Beware that with such DSA-style DH
  74 parameters, a fresh DH key should be created for each use to
  75 avoid small-subgroup attacks that may be possible otherwise.
  76
  77 =item B<-check>
  78
  79 Performs numerous checks to see if the supplied parameters are valid and
  80 displays a warning if not.
  81
  82 =item B<-2>, B<-3>, B<-5>
  83
  84 The generator to use, either 2, 3 or 5. If present then the
  85 input file is ignored and parameters are generated instead. If not
  86 present but I<numbits> is present, parameters are generated with the
  87 default generator 2.
  88
  89 =item B<-rand> I<files>, B<-writerand> I<file>
  90
  91 See L<openssl(1)/Random State Options> for more information.
  92
  93 =item I<numbits>
  94
  95 This option specifies that a parameter set should be generated of size
  96 I<numbits>. It must be the last option. If this option is present then
  97 the input file is ignored and parameters are generated instead. If
  98 this option is not present but a generator (B<-2>, B<-3> or B<-5>) is
  99 present, parameters are generated with a default length of 2048 bits.
 100 The minimim length is 512 bits. The maximum length is 10000 bits.
 101
 102 =item B<-noout>
 103
 104 This option inhibits the output of the encoded version of the parameters.
 105
 106 =item B<-text>
 107
 108 This option prints out the DH parameters in human readable form.
 109
 110 =item B<-C>
 111
 112 This option converts the parameters into C code. The parameters can then
 113 be loaded by calling the get_dhNNNN() function.
 114
 115 =item B<-engine> I<id>
 116
 117 Specifying an engine (by its unique I<id> string) will cause B<dhparam>
 118 to attempt to obtain a functional reference to the specified engine,
 119 thus initialising it if needed. The engine will then be set as the default
 120 for all available algorithms.
 121
 122 =back
 123
 124 =head1 WARNINGS
 125
 126 This command combines the functionality of the L<openssl-dh(1)> and the
 127 L<openssl-gendh(1)> commands in previous OpenSSL versions.
 128 The L<openssl-dh(1)> and L<openssl-gendh(1)> commands are retained for now but
 129 may have different purposes in future versions of OpenSSL.
 130
 131 =head1 NOTES
 132
 133 PEM format DH parameters use the header and footer lines:
 134
 135  -----BEGIN DH PARAMETERS-----
 136  -----END DH PARAMETERS-----
 137
 138 OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42
 139 DH.
 140
 141 This program manipulates DH parameters not keys.
 142
 143 =head1 BUGS
 144
 145 There should be a way to generate and manipulate DH keys.
 146
 147 =head1 SEE ALSO
 148
 149 L<openssl(1)>,
 150 L<openssl-dsaparam(1)>
 151
 152 =head1 COPYRIGHT
 153
 154 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
 155
 156 Licensed under the Apache License 2.0 (the "License").  You may not use
 157 this file except in compliance with the License.  You can obtain a copy
 158 in the file LICENSE in the source distribution or at
 159 L<https://www.openssl.org/source/license.html>.
 160
 161 =cut