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.

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 2000-2021 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>.