6 dhparam - DH parameter manipulation and generation
28 This command is used to manipulate DH parameter files.
34 =item B<-inform DER|PEM>
36 This specifies the input format. The B<DER> option uses an ASN1 DER encoded
37 form compatible with the PKCS#3 DHparameter structure. The PEM form is the
38 default format: it consists of the B<DER> format base64 encoded with
39 additional header and footer lines.
41 =item B<-outform DER|PEM>
43 This specifies the output format, the options have the same meaning as the
46 =item B<-in> I<filename>
48 This specifies the input filename to read parameters from or standard input if
49 this option is not specified.
51 =item B<-out> I<filename>
53 This specifies the output filename parameters to. Standard output is used
54 if this option is not present. The output filename should B<not> be the same
55 as the input filename.
59 If this option is used, DSA rather than DH parameters are read or created;
60 they are converted to DH format. Otherwise, "strong" primes (such
61 that (p-1)/2 is also prime) will be used for DH parameter generation.
63 DH parameter generation with the B<-dsaparam> option is much faster,
64 and the recommended exponent length is shorter, which makes DH key
65 exchange more efficient. Beware that with such DSA-style DH
66 parameters, a fresh DH key should be created for each use to
67 avoid small-subgroup attacks that may be possible otherwise.
71 check if the parameters are valid primes and generator.
75 The generator to use, either 2 or 5. If present then the
76 input file is ignored and parameters are generated instead. If not
77 present but B<numbits> is present, parameters are generated with the
80 =item B<-rand> I<file(s)>
82 a file or files containing random data used to seed the random number
83 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
84 Multiple files can be specified separated by a OS-dependent character.
85 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
90 this option specifies that a parameter set should be generated of size
91 I<numbits>. It must be the last option. If this option is present then
92 the input file is ignored and parameters are generated instead. If
93 this option is not present but a generator (B<-2> or B<-5>) is
94 present, parameters are generated with a default length of 2048 bits.
98 this option inhibits the output of the encoded version of the parameters.
102 this option prints out the DH parameters in human readable form.
106 this option converts the parameters into C code. The parameters can then
107 be loaded by calling the B<get_dh>I<numbits>B<()> function.
111 specifying an engine (by its unique B<id> string) will cause B<dhparam>
112 to attempt to obtain a functional reference to the specified engine,
113 thus initialising it if needed. The engine will then be set as the default
114 for all available algorithms.
120 The program B<dhparam> combines the functionality of the programs B<dh> and
121 B<gendh> in previous versions of OpenSSL and SSLeay. The B<dh> and B<gendh>
122 programs are retained for now but may have different purposes in future
127 PEM format DH parameters use the header and footer lines:
129 -----BEGIN DH PARAMETERS-----
130 -----END DH PARAMETERS-----
132 OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42
135 This program manipulates DH parameters not keys.
139 There should be a way to generate and manipulate DH keys.
143 L<dsaparam(1)|dsaparam(1)>
147 The B<dhparam> command was added in OpenSSL 0.9.5.
148 The B<-dsaparam> option was added in OpenSSL 0.9.6.