DHPARAM(1)			    OpenSSL			    DHPARAM(1)



NAME
       dhparam - DH parameter manipulation and generation

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

DESCRIPTION
       This command is used to manipulate DH parameter files.

OPTIONS
       -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
	   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
	   check if the parameters are valid primes and generator.

       -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(s)
	   a file or files containing random data used to seed the random
	   number generator, or an EGD socket (see RAND_egd(3)).  Multiple
	   files can be specified separated by a OS-dependent character.  The
	   separator is ; for MS-Windows, , for OpenVMS, and : for all others.

       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_dhnumbits() 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 and SSLeay. 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)

HISTORY
       The dhparam command was added in OpenSSL 0.9.5.	The -dsaparam option
       was added in OpenSSL 0.9.6.



1.0.2k				  2017-01-26			    DHPARAM(1)