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] [-2] [-3] [-5] [-engine id] [-rand files] [-writerand file] [-provider name] [-provider-path path] [-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 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, -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 minimim 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
-propquery propq: See "Provider Options" in openssl(1), provider(7), and property(7).

NOTES

This command replaces the dh and gendh commands of previous releases.

HISTORY

The -engine option was deprecated in OpenSSL 3.0.

The -C option was removed in OpenSSL 3.0.

COPYRIGHT

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>.