This command is used to manipulate DH parameter files.
OPTIONS
-inform DER|PEM
This specifies the input format. The DER option uses an ASN1 DER encoded
form compatible with the PKCS#3 DHparameter structure. The PEM form is the
default format: it consists of the DER format base64 encoded with
additional header and footer lines.
-outform DER|PEM
This specifies the output format, the options have the same meaning as the
-inform option.
-infilename
This specifies the input filename to read parameters from or standard input if
this option is not specified.
-outfilename
This specifies the output filename parameters to. Standard output is used
if this option is not present. The output filename should not be the same
as the input filename.
-dsaparam
If this option is used, DSA rather than DH parameters are read or created;
they are converted to DH format. Otherwise, ``strong'' primes (such
that (p-1)/2 is also prime) will be used for DH parameter generation.
DH parameter generation with the -dsaparam option is much faster,
and the recommended exponent length is shorter, which makes DH key
exchange more efficient. Beware that with such DSA-style DH
parameters, a fresh DH key should be created for each use to
avoid small-subgroup attacks that may be possible otherwise.
-2, -5
The generator to use, either 2 or 5. 2 is the default. If present then the
input file is ignored and parameters are generated instead.
-randfile(s)
a file or files containing random data used to seed the random number
generator, or an EGD socket (see RAND_egd(3)).
Multiple files can be specified separated by a OS-dependent character.
The separator is ; for MS-Windows, , for OpenVMS, and : for
all others.
numbits
this option specifies that a parameter set should be generated of size
numbits. It must be the last option. If not present then a value of 512
is used. If this option is present then the input file is ignored and
parameters are generated instead.
-noout
this option inhibits the output of the encoded version of the parameters.
-text
this option prints out the DH parameters in human readable form.
-C
this option converts the parameters into C code. The parameters can then
be loaded by calling the get_dhnumbits() function.
-engine id
specifying an engine (by it's unique id string) will cause req
to attempt to obtain a functional reference to the specified engine,
thus initialising it if needed. The engine will then be set as the default
for all available algorithms.
WARNINGS
The program dhparam combines the functionality of the programs dh and
gendh in previous versions of OpenSSL and SSLeay. The dh and gendh
programs are retained for now but may have different purposes in future
versions of OpenSSL.
NOTES
PEM format DH parameters use the header and footer lines:
