man > openssl-dhparam(1)

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] [-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
           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
       -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 2000-2023 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>.

3.0.13                                       2026-07-29                        OPENSSL-DHPARAM(1SSL)