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1 .\" $NetBSD: openssl_dhparam.1,v 1.14 2015/06/12 17:01:14 christos Exp $
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135 .\" ========================================================================
136 .\"
137 .IX Title "DHPARAM 1"
138 .TH DHPARAM 1 "2015-06-12" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 dhparam \- DH parameter manipulation and generation
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 \&\fBopenssl dhparam\fR
150 [\fB\-inform DER|PEM\fR]
151 [\fB\-outform DER|PEM\fR]
152 [\fB\-in\fR \fIfilename\fR]
153 [\fB\-out\fR \fIfilename\fR]
154 [\fB\-dsaparam\fR]
155 [\fB\-check\fR]
156 [\fB\-noout\fR]
157 [\fB\-text\fR]
158 [\fB\-C\fR]
159 [\fB\-2\fR]
160 [\fB\-5\fR]
161 [\fB\-rand\fR \fIfile(s)\fR]
162 [\fB\-engine id\fR]
163 [\fInumbits\fR]
164 .SH "DESCRIPTION"
165 .IX Header "DESCRIPTION"
166 This command is used to manipulate \s-1DH\s0 parameter files.
167 .SH "OPTIONS"
168 .IX Header "OPTIONS"
169 .IP "\fB\-inform DER|PEM\fR" 4
170 .IX Item "-inform DER|PEM"
171 This specifies the input format. The \fB\s-1DER\s0\fR option uses an \s-1ASN1 DER\s0 encoded
172 form compatible with the PKCS#3 DHparameter structure. The \s-1PEM\s0 form is the
173 default format: it consists of the \fB\s-1DER\s0\fR format base64 encoded with
174 additional header and footer lines.
175 .IP "\fB\-outform DER|PEM\fR" 4
176 .IX Item "-outform DER|PEM"
177 This specifies the output format, the options have the same meaning as the
178 \&\fB\-inform\fR option.
179 .IP "\fB\-in\fR \fIfilename\fR" 4
180 .IX Item "-in filename"
181 This specifies the input filename to read parameters from or standard input if
182 this option is not specified.
183 .IP "\fB\-out\fR \fIfilename\fR" 4
184 .IX Item "-out filename"
185 This specifies the output filename parameters to. Standard output is used
186 if this option is not present. The output filename should \fBnot\fR be the same
187 as the input filename.
188 .IP "\fB\-dsaparam\fR" 4
189 .IX Item "-dsaparam"
190 If this option is used, \s-1DSA\s0 rather than \s-1DH\s0 parameters are read or created;
191 they are converted to \s-1DH\s0 format. Otherwise, \*(L"strong\*(R" primes (such
192 that (p\-1)/2 is also prime) will be used for \s-1DH\s0 parameter generation.
193 .Sp
194 \&\s-1DH\s0 parameter generation with the \fB\-dsaparam\fR option is much faster,
195 and the recommended exponent length is shorter, which makes \s-1DH\s0 key
196 exchange more efficient. Beware that with such DSA-style \s-1DH\s0
197 parameters, a fresh \s-1DH\s0 key should be created for each use to
198 avoid small-subgroup attacks that may be possible otherwise.
199 .IP "\fB\-check\fR" 4
200 .IX Item "-check"
201 check if the parameters are valid primes and generator.
202 .IP "\fB\-2\fR, \fB\-5\fR" 4
203 .IX Item "-2, -5"
204 The generator to use, either 2 or 5. If present then the
205 input file is ignored and parameters are generated instead. If not
206 present but \fBnumbits\fR is present, parameters are generated with the
207 default generator 2.
208 .IP "\fB\-rand\fR \fIfile(s)\fR" 4
209 .IX Item "-rand file(s)"
210 a file or files containing random data used to seed the random number
211 generator, or an \s-1EGD\s0 socket (see \fIRAND_egd\fR\|(3)).
212 Multiple files can be specified separated by a OS-dependent character.
213 The separator is \fB;\fR for MS-Windows, \fB,\fR for OpenVMS, and \fB:\fR for
214 all others.
215 .IP "\fInumbits\fR" 4
216 .IX Item "numbits"
217 this option specifies that a parameter set should be generated of size
218 \&\fInumbits\fR. It must be the last option. If this option is present then
219 the input file is ignored and parameters are generated instead. If
220 this option is not present but a generator (\fB\-2\fR or \fB\-5\fR) is
221 present, parameters are generated with a default length of 2048 bits.
222 .IP "\fB\-noout\fR" 4
223 .IX Item "-noout"
224 this option inhibits the output of the encoded version of the parameters.
225 .IP "\fB\-text\fR" 4
226 .IX Item "-text"
227 this option prints out the \s-1DH\s0 parameters in human readable form.
228 .IP "\fB\-C\fR" 4
229 .IX Item "-C"
230 this option converts the parameters into C code. The parameters can then
231 be loaded by calling the \fBget_dh\fR\fInumbits\fR\fB()\fR function.
232 .IP "\fB\-engine id\fR" 4
233 .IX Item "-engine id"
234 specifying an engine (by its unique \fBid\fR string) will cause \fBdhparam\fR
235 to attempt to obtain a functional reference to the specified engine,
236 thus initialising it if needed. The engine will then be set as the default
237 for all available algorithms.
238 .SH "WARNINGS"
239 .IX Header "WARNINGS"
240 The program \fBdhparam\fR combines the functionality of the programs \fBdh\fR and
241 \&\fBgendh\fR in previous versions of OpenSSL and SSLeay. The \fBdh\fR and \fBgendh\fR
242 programs are retained for now but may have different purposes in future
243 versions of OpenSSL.
244 .SH "NOTES"
245 .IX Header "NOTES"
246 \&\s-1PEM\s0 format \s-1DH\s0 parameters use the header and footer lines:
247 .PP
248 .Vb 2
249 \& \-\-\-\-\-BEGIN DH PARAMETERS\-\-\-\-\-
250 \& \-\-\-\-\-END DH PARAMETERS\-\-\-\-\-
251 .Ve
252 .PP
253 OpenSSL currently only supports the older PKCS#3 \s-1DH,\s0 not the newer X9.42
254 \&\s-1DH.\s0
255 .PP
256 This program manipulates \s-1DH\s0 parameters not keys.
257 .SH "BUGS"
258 .IX Header "BUGS"
259 There should be a way to generate and manipulate \s-1DH\s0 keys.
260 .SH "SEE ALSO"
261 .IX Header "SEE ALSO"
262 \&\fIopenssl_dsaparam\fR\|(1)
263 .SH "HISTORY"
264 .IX Header "HISTORY"
265 The \fBdhparam\fR command was added in OpenSSL 0.9.5.
266 The \fB\-dsaparam\fR option was added in OpenSSL 0.9.6.