5 dhparam - DH parameter manipulation and generation
25 This command is used to manipulate DH parameter files.
31 =item B<-inform DER|PEM>
33 This specifies the input format. The B<DER> option uses an ASN1 DER encoded
34 form compatible with the PKCS#3 DHparameter structure. The PEM form is the
35 default format: it consists of the B<DER> format base64 encoded with
36 additional header and footer lines.
38 =item B<-outform DER|PEM>
40 This specifies the output format, the options have the same meaning as the
43 =item B<-in> I<filename>
45 This specifies the input filename to read parameters from or standard input if
46 this option is not specified.
48 =item B<-out> I<filename>
50 This specifies the output filename parameters to. Standard output is used
51 if this option is not present. The output filename should B<not> be the same
52 as the input filename.
56 If this option is used, DSA rather than DH parameters are read or created;
57 they are converted to DH format. Otherwise, "strong" primes (such
58 that (p-1)/2 is also prime) will be used for DH parameter generation.
60 DH parameter generation with the B<-dsaparam> option is much faster,
61 and the recommended exponent length is shorter, which makes DH key
62 exchange more efficient. Beware that with such DSA-style DH
63 parameters, a fresh DH key should be created for each use to
64 avoid small-subgroup attacks that may be possible otherwise.
68 The generator to use, either 2 or 5. 2 is the default. If present then the
69 input file is ignored and parameters are generated instead.
71 =item B<-rand> I<file(s)>
73 a file or files containing random data used to seed the random number
74 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
75 Multiple files can be specified separated by a OS-dependent character.
76 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
81 this option specifies that a parameter set should be generated of size
82 I<numbits>. It must be the last option. If not present then a value of 512
83 is used. If this option is present then the input file is ignored and
84 parameters are generated instead.
88 this option inhibits the output of the encoded version of the parameters.
92 this option prints out the DH parameters in human readable form.
96 this option converts the parameters into C code. The parameters can then
97 be loaded by calling the B<get_dh>I<numbits>B<()> function.
103 The program B<dhparam> combines the functionality of the programs B<dh> and
104 B<gendh> in previous versions of OpenSSL and SSLeay. The B<dh> and B<gendh>
105 programs are retained for now but may have different purposes in future
110 PEM format DH parameters use the header and footer lines:
112 -----BEGIN DH PARAMETERS-----
113 -----END DH PARAMETERS-----
115 OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42
118 This program manipulates DH parameters not keys.
122 There should be a way to generate and manipulate DH keys.
126 L<dsaparam(1)|dsaparam(1)>
130 The B<dhparam> command was added in OpenSSL 0.9.5.
131 The B<-dsaparam> option was added in OpenSSL 0.9.6.