DHPARAM(1SSL) OpenSSL DHPARAM(1SSL)
NAME
openssl-dhparam, dhparam - DH parameter manipulation and generation
SYNOPSIS
openssl dhparam [-help] [-inform DER|PEM] [-outform DER|PEM] [-in
filename] [-out filename] [-dsaparam] [-check] [-noout] [-text] [-C]
[-2] [-5] [-rand file...] [-writerand file] [-engine id] [numbits]
DESCRIPTION
This command is used to manipulate DH parameter files.
OPTIONS
-help
Print out a usage message.
-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
and default as the -inform option.
-in filename
This specifies the input filename to read parameters from or
standard input if this option is not specified.
-out filename
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.
-check
Performs numerous checks to see if the supplied parameters are
valid and displays a warning if not.
-2, -5
The generator to use, either 2 or 5. If present then the input file
is ignored and parameters are generated instead. If not present but
numbits is present, parameters are generated with the default
generator 2.
-rand file...
A file or files containing random data used to seed the random
number generator. Multiple files can be specified separated by an
OS-dependent character. The separator is ; for MS-Windows, , for
OpenVMS, and : for all others.
[-writerand file]
Writes random data to the specified file upon exit. This can be
used with a subsequent -rand flag.
numbits
This option specifies that a parameter set should be generated of
size numbits. It must be the last option. If this option is present
then the input file is ignored and parameters are generated
instead. If this option is not present but a generator (-2 or -5)
is present, parameters are generated with a default length of 2048
bits.
-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_dhNNNN() function.
-engine id
Specifying an engine (by its unique id string) will cause dhparam
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. 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:
-----BEGIN DH PARAMETERS-----
-----END DH PARAMETERS-----
OpenSSL currently only supports the older PKCS#3 DH, not the newer
X9.42 DH.
This program manipulates DH parameters not keys.
BUGS
There should be a way to generate and manipulate DH keys.
SEE ALSO
dsaparam(1)
COPYRIGHT
Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
1.1.1g 2020-04-21 DHPARAM(1SSL)