focal (1) openssl-dhparam.1ssl.gz

Provided by: openssl_1.1.1f-1ubuntu2.24_amd64 bug

NAME
       openssl-dhparam, dhparam - DH parameter manipulation and generation


SYNOPSIS
       openssl dhparam [-help] [-inform DER|PEM] [-outform DER|PEM] [-in filename] [-out filename] [-dsaparam]
       [-check] [-noout] [-text] [-C] [-2] [-5] [-rand file...]  [-writerand file] [-engine id] [numbits]


DESCRIPTION
       This command is used to manipulate DH parameter files.


OPTIONS
       -help
           Print out a usage message.

       -inform DER|PEM
           This specifies the input format. The DER option uses an ASN1 DER encoded form compatible with the
           PKCS#3 DHparameter structure. The PEM form is the default format: it consists of the DER format
           base64 encoded with additional header and footer lines.

       -outform DER|PEM
           This specifies the output format, the options have the same meaning and default as the -inform
           option.

       -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, -5
           The generator to use, either 2 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.

       -rand file...
           A file or files containing random data used to seed the random number generator.  Multiple files can
           be specified separated by an OS-dependent character.  The separator is ; for MS-Windows, , for
           OpenVMS, and : for all others.

       [-writerand file]
           Writes random data to the specified file upon exit.  This can be used with a subsequent -rand flag.

       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 or -5) is present, parameters are
           generated with a default length of 2048 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.

       -C  This option converts the parameters into C code. The parameters can then be loaded by calling the
           get_dhNNNN() function.

       -engine id
           Specifying an engine (by its unique id string) will cause dhparam to attempt to obtain a functional
           reference to the specified engine, thus initialising it if needed. The engine will then be set as the
           default for all available algorithms.


WARNINGS
       The program dhparam combines the functionality of the programs dh and gendh in previous versions of
       OpenSSL. The dh and gendh programs are retained for now but may have different purposes in future
       versions of OpenSSL.


NOTES
       PEM format DH parameters use the header and footer lines:

        -----BEGIN DH PARAMETERS-----

        -----END DH PARAMETERS-----
       OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42 DH.

       This program manipulates DH parameters not keys.


BUGS
       There should be a way to generate and manipulate DH keys.


SEE ALSO
       dsaparam(1)


       Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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>.