OPENSSL-DHPARAM(1)

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] [-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.

-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 -C option was removed in OpenSSL 3.0.

The -engine option was removed in OpenSSL 4.0.

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>.