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] [-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,  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
       -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>.

3.4.1                                              2025-04-03                              OPENSSL-DHPARAM(1SSL)