5 dhparam - DH parameter manipulation and generation
29 This command is used to manipulate DH parameter files.
37 Print out a usage message.
39 =item B<-inform DER|PEM>
41 This specifies the input format. The B<DER> option uses an ASN1 DER encoded
42 form compatible with the PKCS#3 DHparameter structure. The PEM form is the
43 default format: it consists of the B<DER> format base64 encoded with
44 additional header and footer lines.
46 =item B<-outform DER|PEM>
48 This specifies the output format, the options have the same meaning as the
51 =item B<-in> I<filename>
53 This specifies the input filename to read parameters from or standard input if
54 this option is not specified.
56 =item B<-out> I<filename>
58 This specifies the output filename parameters to. Standard output is used
59 if this option is not present. The output filename should B<not> be the same
60 as the input filename.
64 If this option is used, DSA rather than DH parameters are read or created;
65 they are converted to DH format. Otherwise, "strong" primes (such
66 that (p-1)/2 is also prime) will be used for DH parameter generation.
68 DH parameter generation with the B<-dsaparam> option is much faster,
69 and the recommended exponent length is shorter, which makes DH key
70 exchange more efficient. Beware that with such DSA-style DH
71 parameters, a fresh DH key should be created for each use to
72 avoid small-subgroup attacks that may be possible otherwise.
76 Performs numerous checks to see if the supplied parameters are valid and
77 displays a warning if not.
81 The generator to use, either 2 or 5. If present then the
82 input file is ignored and parameters are generated instead. If not
83 present but B<numbits> is present, parameters are generated with the
86 =item B<-rand file...>
88 A file or files containing random data used to seed the random number
90 Multiple files can be specified separated by an OS-dependent character.
91 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
94 =item [B<-writerand file>]
96 Writes random data to the specified I<file> upon exit.
97 This can be used with a subsequent B<-rand> flag.
101 This option specifies that a parameter set should be generated of size
102 I<numbits>. It must be the last option. If this option is present then
103 the input file is ignored and parameters are generated instead. If
104 this option is not present but a generator (B<-2> or B<-5>) is
105 present, parameters are generated with a default length of 2048 bits.
109 This option inhibits the output of the encoded version of the parameters.
113 This option prints out the DH parameters in human readable form.
117 This option converts the parameters into C code. The parameters can then
118 be loaded by calling the get_dhNNNN() function.
122 Specifying an engine (by its unique B<id> string) will cause B<dhparam>
123 to attempt to obtain a functional reference to the specified engine,
124 thus initialising it if needed. The engine will then be set as the default
125 for all available algorithms.
131 The program B<dhparam> combines the functionality of the programs B<dh> and
132 B<gendh> in previous versions of OpenSSL. The B<dh> and B<gendh>
133 programs are retained for now but may have different purposes in future
138 PEM format DH parameters use the header and footer lines:
140 -----BEGIN DH PARAMETERS-----
141 -----END DH PARAMETERS-----
143 OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42
146 This program manipulates DH parameters not keys.
150 There should be a way to generate and manipulate DH keys.
158 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
160 Licensed under the OpenSSL license (the "License"). You may not use
161 this file except in compliance with the License. You can obtain a copy
162 in the file LICENSE in the source distribution or at
163 L<https://www.openssl.org/source/license.html>.