OPENSSL-DHPARAM(1SSL) OpenSSL OPENSSL-DHPARAM(1SSL)
NAME
openssl-dhparam - DH parameter manipulation and generation
SYNOPSIS
openssl dhparam [-help] [-inform DER|PEM] [-outform DER|PEM] [-in
filename] [-out filename] [-dsaparam] [-check] [-noout] [-text]
[-verbose] [-quiet] [-2] [-3] [-5] [-engine id] [-rand files]
[-writerand file] [-provider name] [-provider-path path] [-provparam
[name:]key=value] [-propquery propq] [numbits]
DESCRIPTION
This command is used to manipulate DH parameter files.
See "EXAMPLES" in openssl-genpkey(1) for examples on how to generate a
key using a named safe prime group without generating intermediate
parameters.
OPTIONS
-help
Print out a usage message.
-inform DER|PEM, -outform DER|PEM
The input format and output format; the default is PEM. The object
is compatible with the PKCS#3 DHparameter structure. See
openssl-format-options(1) for details.
-in filename
This specifies the input file to read parameters from or standard
input if this option is not specified.
-out filename
This specifies the output file to write parameters to. Standard
output is used if this option is not present. The output filename
can be the same as the input filename, which leads to replacing the
file contents. Note that file I/O is not atomic. The output file is
truncated and then written.
-dsaparam
If this option is used, DSA rather than DH parameters are read or
created; they are converted to DH format. Otherwise, safe 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.
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, -3, -5
The generator to use, either 2, 3 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.
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, -3 or -5) is
present, parameters are generated with a default length of 2048
bits. The minimum length is 512 bits. The maximum length is 10000
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.
-engine id
See "Engine Options" in openssl(1). This option is deprecated.
-rand files, -writerand file
See "Random State Options" in openssl(1) for details.
-provider name
-provider-path path
-provparam [name:]key=value
-propquery propq
See "Provider Options" in openssl(1), provider(7), and property(7).
-verbose
This option enables the output of progress messages, which is handy
when running commands interactively that may take a long time to
execute.
-quiet
This option suppresses the output of progress messages, which may be
undesirable in batch scripts or pipelines.
NOTES
This command replaces the dh and gendh commands of previous releases.
SEE ALSO
openssl(1), openssl-pkeyparam(1), openssl-dsaparam(1),
openssl-genpkey(1).
HISTORY
The -engine option was deprecated in OpenSSL 3.0.
The -C option was removed in OpenSSL 3.0.
COPYRIGHT
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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>.
3.5.4 2025-09-30 OPENSSL-DHPARAM(1SSL)
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